Post by: Saladin on May 08, 2010, 06:50:59 am
I do Edexcel AS chemistry!
Post by: Blizz_rb93 on May 08, 2010, 09:15:02 pm
Post by: ksitna on May 08, 2010, 09:25:13 pm
Post by: Blizz_rb93 on May 08, 2010, 09:26:52 pm
yeah i dont really know what to study for unit 3 :/
Here I just found this
1. Make a salt and calculate the percentage yield (hydrated nickel sulfate)
2. make a salt and calculate the percentage yield (ammonium iron(II) sulfate)
3. carry out and interpret results of simple test tube reactions
4. measuring some enthalpy changes
5. finding the enthalpy of combustion of an alcohol
6. finding an enthalpy change that cannot be measured directly
7. reaction of alkanes
8. reaction of alkenes
9. experiment to find the effect of electrostatic force on jets of liquid
10. solubility of simple molecules in different solvents
11. thermal decomposition of group 2 nitrates and carbonates
12. flame tests on compounds of group 1 and 2
13. simple acid-base titrations
14. oxidation of metal and non-metallic elements and ions by halogens
15. disproportion reactions with cold and hot alkali
16. iodine/thiosulfate titration and the determination of purity of potassium iodate(V)
17. reactions between halogens and halide ions/some reactions of the halides
18. factors that influence the rate of chemical reactions
19. effect of temperature, pressure and concentrations on equilibrium
20. reactions of alcohols
21. preparation of organic liquid (reflux and distillation)
22. preparation of a halogenoalkane from an alcohol
23. reactions of the halogenoalkanes.
But I need some worksheets to help me get the idea they want lol
Post by: Saladin on May 09, 2010, 03:36:20 pm
Post by: Blizz_rb93 on May 09, 2010, 04:18:28 pm
There is no need for worksheets. Just do the ppqs from Jan 04 to Jan 2010. That is more than enuf practice!Problem is, they change the syllabus so some stuff from 04 till about 08 wouldn't be included cause of syllabus change.
Post by: Saladin on May 09, 2010, 04:30:08 pm
Problem is, they change the syllabus so some stuff from 04 till about 08 wouldn't be included cause of syllabus change.
There is no real change. You can practice them without fear!
Post by: Blizz_rb93 on May 09, 2010, 04:34:32 pm
There is no real change. You can practice them without fear!Yes there is, there's some points that they stopped bringing in for the new syllabus
If there was no real change? then why did they bother in changing the syllabus ?
Post by: Summer :] on May 09, 2010, 04:46:22 pm
why do we have to add the sulphuric acid slowly when preparing the bromoalkane from alcohol?
Post by: ksitna on May 09, 2010, 06:25:51 pm
does anyone have any notes on these?
Post by: EVIL DOCTOR on May 09, 2010, 06:28:17 pm
i have a question
why do we have to add the sulphuric acid slowly when preparing the bromoalkane from alcohol?
So it will not explode as reaction is exothermic
Post by: Saladin on May 09, 2010, 06:28:31 pm
i dont get how to calculate the percentage yield and error
does anyone have any notes on these?
How about you give a question, and I help you with it. You can post in the Edexcel CHEMISTRY doubts area.
Post by: wrongaccount on May 10, 2010, 12:21:44 am
"Carry out the preparation of an halogenoalkane from an alcohol and
explain why a metal halide and concentrated sulfuric acid should not
be used when making a bromoalkane or an iodoalkane."
why cant Concen. H2SO4 be used neither a metal halide ?
Post by: Summer :] on May 10, 2010, 07:23:20 am
there is this point the syllabus that i dont understand please could someone answer this before the exam ??
"Carry out the preparation of an halogenoalkane from an alcohol and
explain why a metal halide and concentrated sulfuric acid should not
be used when making a bromoalkane or an iodoalkane."
why cant Concen. H2SO4 be used neither a metal halide ?
this point is wrong though :s we use concentrated sulphuric acid to make bromoalkanes!! and a metal halide
but the point might be referring of why it should not be used
because it releases many by products
such brome or iodine depending on which halogenoalkane you are making...and it releases sulphur dioxide
Post by: Uchia on May 10, 2010, 09:05:17 am
sulphuric acid is a stong enough oxidising agent so a concentrated sulphuric acid couldn't be used because it will further get reduced it self and will oxidise the halide ion to form iodine or bromine resulting in now HI or HBr for the reaction with alcohol to form haloalakane.
Post by: Saladin on May 10, 2010, 09:09:12 am
Summer don't confuse the guy i'll tell you the right answer
sulphuric acid is a stong enough oxidising agent so a concentrated sulphuric acid couldn't be used because it will further get reduced it self and will oxidise the halide ion to form iodine or bromine resulting in now HI or HBr for the reaction with alcohol to form haloalakane.
You guys are wrong.
You see, the Bromine and Iodine ions are very powerful reducing agennts compared to that of Chlorine, and would result in further reactions, that would not form other products. http://www.chemguide.co.uk/inorganic/group7/halideions.html#top. This site will help u understand the whole thing.
Post by: Uchia on May 10, 2010, 09:26:19 am
it doesn't matter in what way you put because they both stands for the same answer but the problem is you shouldn't mix up when writing which one is the oxidising and which one is the reducing agent
Post by: Saladin on May 10, 2010, 09:28:24 am
lol mysterious i said the same thing but in the opposite way i said sulpuric acid is a strong oxidising agen (poor reducing agent) and bromine ions and iodide ions they get oxidised which means that they are poor oxidising agents and strong reducing agents
it doesn't matter in what way you put because they both stands for the same answer but the problem is you shouldn't mix up when writing which one is the oxidising and which one is the reducing agent
My apologies, i intended it for the person above u. lol
Post by: wrongaccount on May 10, 2010, 11:18:34 am
and damlaj im a SHE :D
Post by: Saladin on May 10, 2010, 11:20:37 am
thanks alot both of you :D :D i appreciate it :)
and damlaj im a SHE :D
LOL
Post by: Uchia on May 10, 2010, 03:29:45 pm
Post by: Meticulous on May 10, 2010, 04:58:35 pm
" 25 cm3 of potassium iodate (V) solution was added to excess potassium iodide solution. The iodine liberated required 30 cm3 of 0.5 mol dm-3 sodium thiosulphate. Calculate the concentration of the potassium iodate (V) solution."
Needed ASAP.
Thanks in advance.
Post by: Uchia on May 10, 2010, 05:04:38 pm
Post by: Meticulous on May 10, 2010, 05:06:31 pm
Post by: Meticulous on May 10, 2010, 06:30:24 pm
Post by: Uchia on May 10, 2010, 06:44:06 pm
Post by: Meticulous on May 10, 2010, 06:45:34 pm
Post by: Uchia on May 10, 2010, 08:06:57 pm
Post by: Meticulous on May 10, 2010, 08:13:16 pm
Post by: Uchia on May 10, 2010, 09:15:26 pm
Post by: Meticulous on May 10, 2010, 09:32:22 pm
Post by: ksitna on May 10, 2010, 10:00:10 pm
Post by: ksitna on May 10, 2010, 10:00:57 pm
Post by: Saladin on May 11, 2010, 03:40:02 am
I need help with this question:
" 25 cm3 of potassium iodate (V) solution was added to excess potassium iodide solution. The iodine liberated required 30 cm3 of 0.5 mol dm-3 sodium thiosulphate. Calculate the concentration of the potassium iodate (V) solution."
Needed ASAP.
Thanks in advance.
Can you please give the exact question paper for this, I need to see the equations of the reaction to give you the answer.
Post by: Summer :] on May 11, 2010, 06:10:36 am
You guys are wrong.
You see, the Bromine and Iodine ions are very powerful reducing agennts compared to that of Chlorine, and would result in further reactions, that would not form other products. http://www.chemguide.co.uk/inorganic/group7/halideions.html#top. This site will help u understand the whole thing.
with Bromine, it would just form HBR, MHSO4 (m for the metal), Br2, SO2, H20
check the sulphur's oxidation number in MHSO4 its (+6) and in S02 (its +4) - it has been reduced furthermore where there was a decrease in the oxidation number
with Iodine because its a stronger reducing agent it would cause the sulphur to be reduced further more
so H2S is formed..
again check the sulphur's oxidation number MHSO4 (+6) and in S02 (+4) and H2S (-2) - so has been reduced alot due the to the stronger reducing agent which is Iodine.
but you dont need that for the organic part, just the part about redox reactions of halogens..
Post by: Blizz_rb93 on May 11, 2010, 10:21:50 pm
so please if anyone can help me understand these questions
2) This question is about two isomeric alcohols, X and Y, each with molar mass 60g mol-1
A solution of potassium dichromate(VI) in dilute sulfuric acid is added to each alcohol. Both alcohols cause the same color change of the mixture on heating.
a) A colorless liquid, B, is distilled from the mixture containing alcohol X.
The liquid B forms a red precipitate when it is boiled with Benedict's or Fehling's solution.
Give the displayed formula of liquid B, and the name of alcohol X.
Liquid B
Name of alcohol X _______________________________
b) A colorless liquid, C, is distilled from the mixture containing alcohol Y.
C does not react when it is boiled with Benedict's or Fehling's solution
Give the names of liquid C and alcohol Y
Liquid C __________________________
Alcohol Y ___________________________
__________________________________________________________________________
That's for question 2, here's question 3.. i know it's kinda long :( but i need help on this so im very sorry
3) This question is about Calcium hydroxide, Ca(OH)2
The solubility of calcium hydroxide in water can be found by titrating a saturated solution of calcium hydroxide with hydrochloric acid of known concentration.
a) Describe how you would make a saturated solution of calcium hydroxide suitable for use in this titration. Do not describe the subsequent titration procedure.
b) 10.0 cm3 portions of the saturated solution are placed in a conical flask and titrated with 0.0500 mol dm-3 hydrochloric acid added from a burette
i) Name the apparatus used to measure the 10.0 cm3 portions
ii) Suggest a suitable indicator for this titration and state the color change you would expect to see at the end point.
c) The following results were obtained
Titration numbers | 1 | 2 | 3 |
_____________________________________________________________________________
Final burette reading/cm3 | 19.20 | 28.05 | 37.10 |
_____________________________________________________________________________
Initial burette reading/cm3 | 10.00 | 19.20 | 28.15 |
_____________________________________________________________________________
Titre/ cm 3 | 9.20 | 8.85 | 8.95 |
____________________________________________________________________________
i) suggest why the first titre should be disregarded.
The rest i know
Thank you all in advance! <33
Post by: vanibharutham on May 12, 2010, 04:44:08 am
This means that they are isomers of C3H8O
A solution of potassium dichromate(VI) in dilute sulfuric acid is added to each alcohol. Both alcohols cause the same color change of the mixture on heating.
They both were oxidized so it cant be a tertiary alcohol
a) A colorless liquid, B, is distilled from the mixture containing alcohol X.
The liquid B forms a red precipitate when it is boiled with Benedict's or Fehling's solution.
This means that it has been oxidized further so liquid B must be propanal
CH3CH2CHO
And alcohol X must be CH3CH2CH2OH
b) A colorless liquid, C, is distilled from the mixture containing alcohol Y.
C does not react when it is boiled with Benedict's or Fehling's solution
Not oxidized further so it must be Propanone - CH3C=OCH3
And the alcohol Y must be a secondary alcohol CH3CH(OH)CH3
Post by: vanibharutham on May 12, 2010, 05:04:11 am
The solubility of calcium hydroxide in water can be found by titrating a saturated solution of calcium hydroxide with hydrochloric acid of known concentration.
a) Describe how you would make a saturated solution of calcium hydroxide suitable for use in this titration. Do not describe the subsequent titration procedure.
Not sure about this one....
Add a known amount of Ca(OH)2 to water and keep stirring. When no more dissolves start heating it. When the solution begins to boil keep adding more Ca(OH)2 while you are still heating it, until no more dissolves.
b) 10.0 cm3 portions of the saturated solution are placed in a conical flask and titrated with 0.0500 mol dm-3 hydrochloric acid added from a burette
i) Name the apparatus used to measure the 10.0 cm3 portions
Pipette
ii) Suggest a suitable indicator for this titration and state the color change you would expect to see at the end point
Phenolphthalein... It is in basic conditions at the start so it will be purple. At the end point it will be colourless
i) suggest why the first titre should be disregarded.
the titre should be disregarded as it was probably a check titration. Furthermore, the titre was more that 0.1cm³ off from the other two values. Titration is a precision method of volumetric analysis and it should be disregarded because it is too far off from the other values
Post by: Meticulous on May 12, 2010, 10:57:18 am
Thanks in advance.
Question paper: http://www.xtremepapers.net/Edexcel/Chemistry/2006%20Jan/6243_02_que_20060118.pdf
Mark Scheme: http://www.xtremepapers.net/Edexcel/Chemistry/2006%20Jan/6243_02_rms_20060125.pdf
Needed ASAP.
Post by: Tammy on May 12, 2010, 12:02:58 pm
The balance used to weigh the magnesium carbonate is accurate to +-0.01 g. Calculate the percentage error in the mass of the magnesium carbonate weighed. ((weighed MgCO3: 0.21g))
the correct answer is 0.02
-----
0.21
Why is it 0.02 not 0.01?? and when do we write it as 0.01??
Thanks in advance peeps
Post by: Blizz_rb93 on May 12, 2010, 12:52:54 pm
Post by: Saladin on May 12, 2010, 01:39:10 pm
How do we calculate the solubility of a substance???
It is the number of grams that can be dissolved divided by the volume of water. You do not need to calculate it for the examination.
Post by: ksitna on May 12, 2010, 02:23:07 pm
This question is about two isomeric alcohols, X and Y, each with molar mass 60g mol-1liquid b is propan-1-ol
This means that they are isomers of C3H8O
A solution of potassium dichromate(VI) in dilute sulfuric acid is added to each alcohol. Both alcohols cause the same color change of the mixture on heating.
They both were oxidized so it cant be a tertiary alcohol
a) A colorless liquid, B, is distilled from the mixture containing alcohol X.
The liquid B forms a red precipitate when it is boiled with Benedict's or Fehling's solution.
This means that it has been oxidized further so liquid B must be propanal
CH3CH2CHO
And alcohol X must be CH3CH2CH2OH
b) A colorless liquid, C, is distilled from the mixture containing alcohol Y.
C does not react when it is boiled with Benedict's or Fehling's solution
Not oxidized further so it must be Propanone - CH3C=OCH3
And the alcohol Y must be a secondary alcohol CH3CH(OH)CH3
Post by: vanibharutham on May 12, 2010, 02:30:28 pm
liquid b is propan-1-ol
Nope, liquid B is obtained from Distillation of Alcohol X
X = Propan-1-ol
B = Propanal
Post by: ksitna on May 12, 2010, 02:42:29 pm
Post by: Summer :] on May 12, 2010, 03:34:52 pm
How do we calculate the solubility of a substance???
grams dissolved in the water
its just the basic equation of moles that you should use
no of moles = mass/ Mr
find the mass..thats all..
Post by: Summer :] on May 12, 2010, 03:39:00 pm
i have a question about percentage error.....
The balance used to weigh the magnesium carbonate is accurate to +-0.01 g. Calculate the percentage error in the mass of the magnesium carbonate weighed. ((weighed MgCO3: 0.21g))
the correct answer is 0.02
-----
0.21
Why is it 0.02 not 0.01?? and when do we write it as 0.01??
Thanks in advance peeps
because
it says +- 0.01
therefore the range could be 0.21 - 0.01
and 0.21 + 0.01
so add those values together 0.01 + 0.01 = 0.02
its always this way i guess..thats what my teacher told us *shrugs* ::)
Post by: ksitna on May 12, 2010, 04:40:35 pm
So in Acid-Base equilibrium when were trying to find the pH of a buffer solution, is the rule:
pH = pKa + log([A – ] ÷ [HA])
OR
pH = pKa - log([A – ] ÷ [HA])
Because in the book they're using the one with the -log and in some questions in the pastpapers they're using the +log. Which one is it exactly?
we have to use log in AS chemistry???
Post by: luluabdl on May 12, 2010, 04:43:21 pm
we have to use log in AS chemistry???
Sorry wrong post, this is A2 :)
Post by: ksitna on May 12, 2010, 04:49:43 pm
Sorry wrong post, this is A2 :)
ohh okie
jeez man u freaked me out!!!!
Post by: ksitna on May 12, 2010, 05:05:26 pm
can someone help me?
Post by: Tammy on May 12, 2010, 05:13:12 pm
because
it says +- 0.01
therefore the range could be 0.21 - 0.01
and 0.21 + 0.01
so add those values together 0.01 + 0.01 = 0.02
its always this way i guess..thats what my teacher told us *shrugs* ::)
Alright!!! Thanks!!!
Post by: Summer :] on May 12, 2010, 05:34:50 pm
Alright!!! Thanks!!!
your welcome! By the way i just asked about
if it says percentage error
then you
(2 x error) / divide by whatever mass X 100
like i said previously
if it says its an error (not percentage)
multiply error by the mass or volume provided / 100
Post by: Summer :] on May 12, 2010, 05:36:06 pm
I'll post the question if anyone is bothered or is not busy
Post by: Saladin on May 12, 2010, 07:07:41 pm
Please state the paper number.
Post by: coatseville on May 12, 2010, 07:35:11 pm
i need help with percentage yields
can someone help me?
For this you use the formula actual yield / theoretical yield x 100.
Post by: ksitna on May 12, 2010, 08:01:36 pm
and can someone tell me where i can find specimen unit 3b?
Post by: Blizz_rb93 on May 12, 2010, 08:14:16 pm
Question 4. branch f) only
Here's the question paper and markscheme attached below
Post by: Meticulous on May 12, 2010, 08:31:17 pm
When adding alkali to acid, it says:
"Swirl / rinse in drops solution in neck of flask (1)"
what is that supposed to mean?
Post by: Saladin on May 12, 2010, 08:33:54 pm
Please any body...a quick question.
When adding alkali to acid, it says:
"Swirl / rinse in drops solution in neck of flask (1)"
what is that supposed to mean?
This basically means that when adding an acid to a base, you need to keep swirling it. Move it and jerk it in a circular motion. Because often, drops dont go straight to the liquid, the often stay on the side of the conical flask.
Post by: Meticulous on May 12, 2010, 08:43:18 pm
Post by: Blizz_rb93 on May 12, 2010, 08:45:56 pm
It would be HIGHLY appreciated!!
Thank you.
Post by: Saladin on May 12, 2010, 08:46:38 pm
Can someone help me with this question from Jan 2010 unit 3b..
Question 4. branch f) only
Here's the question paper and markscheme attached below
Answering now!
Post by: Saladin on May 12, 2010, 08:49:07 pm
Can someone please answer my question!
It would be HIGHLY appreciated!!
Thank you.
First calculate the predicted volume:
This first part is EXACTLY what you did in part (a)
Then just substitute:
Post by: Blizz_rb93 on May 12, 2010, 08:55:44 pm
First calculate the predicted volume:THANK YOU SO MUCH!!!! <333 rep for u :D
This first part is EXACTLY what you did in part (a)
Then just substitute:
Post by: Saladin on May 12, 2010, 08:56:15 pm
THANK YOU SO MUCH!!!! <333 rep for u :D
Just doin my job. Pray for me please.
Post by: Summer :] on May 13, 2010, 06:27:55 am
I will answer.
Please state the paper number.
January 2009 paper the old syllabus
last question
i solved everything...just the last question..oh you might be doing the exam now :( its too late!
Post by: wakemeup on May 14, 2010, 04:37:08 pm
Post by: Kim on May 14, 2010, 04:39:49 pm
I still don't understand properly as to why the stability of carbonates and nitrates of group 2 increases down the group. Could someone explain it to me clearly? I've read 2 books and both just really confuse me.
well as u go down the group the cationic size increases
so there is less polarisation (as the cation is big whereas for polarisation the cation should be small and the anion big)
less weakening of the CO or NO bond
thus the thernal stability increases
Post by: wakemeup on May 14, 2010, 04:48:12 pm
Post by: Blizz_rb93 on May 14, 2010, 10:33:53 pm
- Buckminsterfullerene is a carbon molecule with formula C60 which can trap metal ions its structure. Which of the following compounds of buckminsterfullerene would give a line of mass/charge ratio at 837.3 in a mass spectrometer??
A) Na4C60
B) K3C60
C) Ca3C60
D) AgC60
The markscheme says it's B but i dont get how they got it? and how do u find out the mass/charge ratio at 837.3 in the mass spectrometer?
Post by: Uchia on May 15, 2010, 07:44:29 am
the mr for k is 39.1
so (39.1*3) +(60*12) = 837.3
Post by: Blizz_rb93 on May 15, 2010, 08:24:38 am
answer is b just find the mroh lol ok thats easy XD
the mr for k is 39.1
so (39.1*3) +(60*12) = 837.3
Post by: Summer :] on May 15, 2010, 12:52:01 pm
well as u go down the group the cationic size increases
so there is less polarisation (as the cation is big whereas for polarisation the cation should be small and the anion big)
less weakening of the CO or NO bond
thus the thernal stability increases
as you go down the group
the cationic size increases ( they are less polarising because the are more inner shell electrons repelling the outermost electrons therefore the positive nucleus has less control over its outermost electrons so its less likely to polarise the electrons of the anion towards)
they become less polarising...they are less likely to polarise the anion to break it apart and produce different compounds so they are more stable..less likely to break
so you need more heat to compensate for this weak polarising effect in order to break the compound apart to form other compounds..
Post by: Summer :] on May 15, 2010, 12:52:55 pm
Post by: Meticulous on May 15, 2010, 12:55:26 pm
Post by: Summer :] on May 15, 2010, 01:00:46 pm
You don't need infrared spectroscopy.
yup we do,its included in our syllabus
im taking the edexcel new syllabus starting from 09 or 08 i forgot
maybe you take the old one :P ?
Post by: Meticulous on May 15, 2010, 01:48:32 pm
Post by: Kim on May 15, 2010, 01:55:52 pm
I'm tgking thd new syllabus. And it is not included in the syllabus, only the booj. Prove me wrong.
i am sorry to say dude but it is there
Post by: Meticulous on May 15, 2010, 02:09:16 pm
Post by: Kim on May 15, 2010, 02:11:13 pm
Show it to me, written in the SYLLABUS. I'd really like to be sure.its present in all the txtbks isnt that proof enough???
i study from 2 txtbks and they both have it
Post by: Meticulous on May 15, 2010, 02:19:04 pm
Check http://www.edexcel.com/migrationdocuments/GCE%20New%20GCE/spec-gce-chemistry.pdf
You won't find Infrared spectroscopy.
Anyway, do whatever you want to do.
Post by: Kim on May 15, 2010, 02:28:16 pm
No. Its not good enough for me.
Check http://www.edexcel.com/migrationdocuments/GCE%20New%20GCE/spec-gce-chemistry.pdf
You won't find Infrared spectroscopy.
Anyway, do whatever you want to do.
go to page 63 of the syllabus
Post by: raimunts on May 15, 2010, 05:31:29 pm
This is probably asking a lot....so even if u can't [or arent generous enuff] to share notes, can you PLEASE outline all of the things u need to know about ORGANIC CHEMISTRY for unit 1 and 2?
Post by: Darth Austrakast on May 15, 2010, 05:59:31 pm
well there u go--here r some links on chemistry i was generous enough to post though not-so-generous-enough
to categorize according to the new syllabus :P ;)
For Unit 1 Organic Chemistry ----
here are some notes i have attached
Post by: Darth Austrakast on May 15, 2010, 06:02:38 pm
Post by: raimunts on May 15, 2010, 11:25:35 pm
Post by: Darth Austrakast on May 16, 2010, 03:43:43 am
Post by: Summer :] on May 16, 2010, 07:17:46 pm
No. Its not good enough for me.
Check http://www.edexcel.com/migrationdocuments/GCE%20New%20GCE/spec-gce-chemistry.pdf
You won't find Infrared spectroscopy.
Anyway, do whatever you want to do.
It's included the book as well..
which book do you use?
Post by: Meticulous on May 16, 2010, 07:46:15 pm
I use the standardized edexcel book. It's included there, but not innthe syllabus.
Anyway, could anyone jot down a synopsis of IR Spectroscopy?
Thanks in advance.
Post by: Igcseboy on May 16, 2010, 07:49:42 pm
thanxx
Post by: vanibharutham on May 16, 2010, 09:05:38 pm
2H2(g) + O2(g) ? 2H2O(g)
If all volumes are measured at 110 °C and one atmosphere pressure, the volume of steam
produced after 50 cm³ of hydrogen react completely with 25 cm³ of oxygen is
A 25 cm³
B 50 cm³
C 75 cm³
D 100 cm³
AVOGADRO's LAW
"Equal volumes of ideal or perfect gases, at the same temperature and pressure, contain the same number of molecules."
At the given temperature and pressure,
1 mole = 25cm³
therefore,
the 2 moles of steam = 50cm³
Post by: Igcseboy on May 16, 2010, 09:13:17 pm
Post by: vanibharutham on May 16, 2010, 09:21:06 pm
d i) C9H20
ii) 3-ethyl-4-methylhexane
Post by: Summer :] on May 16, 2010, 09:45:29 pm
It's included in the syllabus. But in the A@ section; Unit 4.
I use the standardized edexcel book. It's included there, but not innthe syllabus.
Anyway, could anyone jot down a synopsis of IR Spectroscopy?
Thanks in advance.
Okay i find this site useful, check it out
http://www.chemguide.co.uk/analysismenu.html#top
Post by: Meticulous on May 16, 2010, 10:47:11 pm
Post by: raimunts on May 17, 2010, 04:49:44 pm
To show sharing of electrons in covalent compounds or transfer of electrons in ionic compounds which one should be used?
1. Dot AND Cross diagrams: This shows dots for electrons of one atom/ion and crosses for electrons of the other atom/ion. This way of showing electrons makes it very clear that the electrons from one atom is being transferred to another atom resulting in the formation of ions [ionic bonding] or showing that electrons from BOTH the atoms are being shared [covalent bonding.] The problem with this display method is written below.
2. Dot OR Cross diagrams: This shows ONLY either dots [dots for all electrons] or crosses [crosses for all electrons. This way is more scientifically accurate, because using two different types of symbols for electrons may imply that the electrons of different atoms are not the same, which is not true. If only dots or only crosses are used, then it is scientifically accurate because ALL electrons are the same.
Disadvantage of this method of display over the above one, is that showing BOTH dots and crosses makes it clear that electrons from both atoms are being shared.
So, which one should be used in the Edexcel AS Levels?
Thanx in advance for helping :)
Post by: Meticulous on May 17, 2010, 04:59:43 pm
It's a MUST.
Post by: raimunts on May 17, 2010, 05:13:05 pm
Post by: Meticulous on May 17, 2010, 06:16:51 pm
Post by: Igcseboy on May 17, 2010, 06:28:32 pm
You prolly mean 24 d i) and ii)
d i) C9H20
ii) 3-ethyl-4-methylhexane
no the question in which we have to find enthalpy change using mean bond enthalpy....
Post by: Saladin on May 17, 2010, 06:56:43 pm
no the question in which we have to find enthalpy change using mean bond enthalpy....
Post by: Saladin on May 17, 2010, 06:59:17 pm
Post by: raimunts on May 17, 2010, 07:24:09 pm
given there are 4 compunds A, B, C and D...and: A + B --> C + D
and standard enthalpy of formation/combustion is given for any three. Is it possible to find the remaining one from those three?
If it is, then what is the relationship?
Post by: vanibharutham on May 17, 2010, 08:49:04 pm
in the attached file
1 = standard enthalpy of combustion of A
2 = standard enthalpy of formation of A
3 = standard enthalpy of formation of B
4 = standard enthalpy of formation of C
NB. O2 does an enthalpy of formation of 0 kJ/mol
using Hess's Law
1 = 3 + 4 - 2
just substitute in the values
Post by: obstacle26 on May 17, 2010, 10:04:08 pm
A Na4C60
B K3C60
C Ca3C60
D AgC60
Answer is B , can some body explain the logic?
Post by: Meticulous on May 17, 2010, 10:24:56 pm
so calc the Mr of all compounds. It's B.
Post by: raimunts on May 18, 2010, 12:54:45 am
One element must be O2 for it to be an enthalpy of combustion
in the attached file
1 = standard enthalpy of combustion of A
2 = standard enthalpy of formation of A
3 = standard enthalpy of formation of B
4 = standard enthalpy of formation of C
NB. O2 does an enthalpy of formation of 0 kJ/mol
using Hess's Law
1 = 3 + 4 - 2
just substitute in the values
Thanks a lot. Crystal clear. So it's only for enthalpy change of combustion...nothing for formation?
Post by: raimunts on May 18, 2010, 01:56:10 am
Post by: Darth Austrakast on May 18, 2010, 02:12:10 am
Post by: raimunts on May 18, 2010, 02:49:21 am
Post by: Darth Austrakast on May 18, 2010, 03:20:49 am
Post by: Igcseboy on May 19, 2010, 08:58:09 am
Post by: Igcseboy on May 19, 2010, 09:06:29 am
Post by: Kim on May 19, 2010, 09:10:10 am
6CH01 june 2009 mcq 5 ????
the answer is d
if u wanna know how ill tell ya
Post by: Igcseboy on May 19, 2010, 09:14:42 am
the answer is d
if u wanna know how ill tell ya
yes i want to ... thanxzz
Post by: Kim on May 19, 2010, 09:19:23 am
yes i want to ... thanxzz
well to calculate no of ions u need to first find no. of moles
n=m/mr=17.1/342=0.05
then u have to find the no of ions
no.of ions=0.05 x 6.02x10^23=3.01x10^22
i mole of aluminium sulphate has 2 aluminium ions and 3 sulphate ions
so as u have to find number of sulphate ions multiply the above ans by 3 and u get 9.02x10^22
Post by: Kim on May 19, 2010, 09:20:19 am
Post by: Igcseboy on May 19, 2010, 09:29:20 am
cud u plzz do the 15th mcq also plzzz
Post by: Kim on May 19, 2010, 09:35:24 am
ok thanx aloot
cud u plzz do the 15th mcq also plzzz
yeh sure
the answer is A
because if ge and f were to form a compound the formula wud be gef4
as ge is in group 4 and f in group 1
and the rest all are possible
Post by: Igcseboy on May 19, 2010, 09:40:05 am
for 11 how can we tell ??? (for the same types if come in exam)
Post by: Kim on May 19, 2010, 09:45:01 am
Jan 2010 MCQ 11 an 12
for 11 how can we tell ??? (for the same types if come in exam)
well for 12 the answer is A because mg is a metal and oxygen a non metal
and the bonding between a metal and non metal is ionic bonding
well for 11 the answer isC although i dunno why ill see if i can figure it out
Post by: Saladin on May 19, 2010, 10:14:52 am
Jan 2010 MCQ 11 an 12
for 11 how can we tell ??? (for the same types if come in exam)
For Question 12: The bonding between a metal and a non-metal is ionic. Thus A. But the further reason is that Mg and O bonding, there is almost no distortion of the ionic bond.
For Question 11: The nickel ion is green in color. And since it has a positive charge, it will go towards the negative electrode. The sulphate ion however, is colorless, and thus, even if it goes to the negative electrode, you cannot see it. Thus the answer is C.
Post by: Igcseboy on May 19, 2010, 04:21:45 pm
For Question 12: The bonding between a metal and a non-metal is ionic. Thus A. But the further reason is that Mg and O bonding, there is almost no distortion of the ionic bond.
For Question 11: The nickel ion is green in color. And since it has a positive charge, it will go towards the negative electrode. The sulphate ion however, is colorless, and thus, even if it goes to the negative electrode, you cannot see it. Thus the answer is C.
ok thanxx
but why MgO is not ionic covalent as there is distortion ????
Post by: Darth Austrakast on May 19, 2010, 04:25:23 pm
Post by: Igcseboy on May 19, 2010, 05:14:40 pm
When 10cm^3 of the hydrocarbon is burned in 70 cm^3 of oxygen (in excess), the final gaseous mixture contains 30cm^3 carbondioxide and 20 cm^3 of unreacted Oxygen. All gaseous volumes are measured under identical conditions.
What is the formula of the hydrocarbon?
A.C2H6
B.C3H6
C.C3H8
D.C4H10
the answer is C... but how to get at this
i got this question in my mock exam
another one
Which of these sample of gas contains the same number of atoms as 1g of hydrogen gas?
A.22g of carbondioxide
B.8g of methane
C.20g of neon
D.8g of ozone(O3)
My teacher told the answer is C...... but am not sure how to get at it???
any help will be appreciated :)
Post by: Kim on May 19, 2010, 05:46:02 pm
1g of hydrogen has 1 mole
as 1/1=1
the same for neon
20/20.2(molar mass)=0.99=1
Post by: Igcseboy on May 19, 2010, 05:52:53 pm
well for the second one
1g of hydrogen has 1 mole
as 1/1=1
the same for neon
20/20.2(molar mass)=0.99=1
but hydrogen is H2 right so the number of moles is 1/2=0.5 :S:S ????
Post by: Kim on May 19, 2010, 05:54:24 pm
yup i forgot about that sorry
but hydrogen is H2 right so the number of moles is 1/2=0.5 :S:S ????
was just about to tell ya
Post by: Igcseboy on May 19, 2010, 05:59:09 pm
Post by: Kim on May 19, 2010, 06:00:47 pm
so ........... wat is correct????
u have to use h2 and Ne2 so follow austrakasts ans
i dunno if i got that name right lol
Post by: Saladin on May 19, 2010, 06:07:31 pm
A pure hydrocarbon is used in bottled gas for cooking and heaing.
When 10cm^3 of the hydrocarbon is burned in 70 cm^3 of oxygen (in excess), the final gaseous mixture contains 30cm^3 carbondioxide and 20 cm^3 of unreacted Oxygen. All gaseous volumes are measured under identical conditions.
What is the formula of the hydrocarbon?
A.C2H6
B.C3H6
C.C3H8
D.C4H10
the answer is C... but how to get at this
i got this question in my mock exam
another one
Which of these sample of gas contains the same number of atoms as 1g of hydrogen gas?
A.22g of carbondioxide
B.8g of methane
C.20g of neon
D.8g of ozone(O3)
My teacher told the answer is C...... but am not sure how to get at it???
any help will be appreciated :)
Hoping to answer this soon.
Post by: Saladin on May 19, 2010, 06:31:21 pm
A pure hydrocarbon is used in bottled gas for cooking and heaing.
When 10cm^3 of the hydrocarbon is burned in 70 cm^3 of oxygen (in excess), the final gaseous mixture contains 30cm^3 carbondioxide and 20 cm^3 of unreacted Oxygen. All gaseous volumes are measured under identical conditions.
What is the formula of the hydrocarbon?
A.C2H6
B.C3H6
C.C3H8
D.C4H10
the answer is C... but how to get at this
i got this question in my mock exam
another one
Which of these sample of gas contains the same number of atoms as 1g of hydrogen gas?
A.22g of carbondioxide
B.8g of methane
C.20g of neon
D.8g of ozone(O3)
My teacher told the answer is C...... but am not sure how to get at it???
any help will be appreciated :)
Can you please send me the actual question paper.
Post by: Saladin on May 19, 2010, 07:37:21 pm
A pure hydrocarbon is used in bottled gas for cooking and heaing.
When 10cm^3 of the hydrocarbon is burned in 70 cm^3 of oxygen (in excess), the final gaseous mixture contains 30cm^3 carbondioxide and 20 cm^3 of unreacted Oxygen. All gaseous volumes are measured under identical conditions.
What is the formula of the hydrocarbon?
A.C2H6
B.C3H6
C.C3H8
D.C4H10
the answer is C... but how to get at this
i got this question in my mock exam
another one
Which of these sample of gas contains the same number of atoms as 1g of hydrogen gas?
A.22g of carbondioxide
B.8g of methane
C.20g of neon
D.8g of ozone(O3)
My teacher told the answer is C...... but am not sure how to get at it???
any help will be appreciated :)
For (a) 3 moles of CO2 is formed. And 2 moles of O2 was used to form water. Thus 8 hydrogens were used.
Thus, C3H8
(b) 1 gram of H2 will mean 1 mole of H2. 20 grams of Ne will mean 1 mole of Ne. Thus same number of atoms as Hydrogen.
Post by: Kim on May 19, 2010, 07:53:15 pm
and how u got it??thanks
Post by: Uchia on May 19, 2010, 08:00:51 pm
Post by: Kim on May 19, 2010, 08:02:43 pm
6ch01
Post by: Uchia on May 19, 2010, 08:04:49 pm
if it was unit 1 then D cz as you can see this question depends on the polarising power and the polarising power depends on the ionic charge and radius
Post by: Meticulous on May 19, 2010, 08:04:56 pm
hey cud sum1 tell the answer to jan 2009 q2
and how u got it??thanks
There is a law in physics called coulombs law of electrostatic forces of attraction:
F= kQ1 Q2 / r2
Therefore, the force is affected by charge and radius. Got that?
Post by: Kim on May 19, 2010, 08:07:07 pm
ya i got it
and also same paper q6 a and b
Post by: Saladin on May 19, 2010, 08:32:42 pm
hey cud sum1 tell the answer to jan 2009 q2
and how u got it??thanks
In 30 minutes.
Post by: Uchia on May 19, 2010, 09:00:09 pm
in part b 4 of the C-H bonds have been broken so its a mean bond enthalpy cz they are all same bonds and a mean value was taken for all of them
Post by: Kim on May 19, 2010, 09:11:07 pm
as you can see in part a the CH4 became CH3 which means a C-H bond has been broken therefore it is a bond enthalpy
in part b 4 of the C-H bonds have been broken so its a mean bond enthalpy cz they are all same bonds and a mean value was taken for all of them
thank u sooooooo much
Post by: raimunts on May 19, 2010, 11:59:54 pm
Post by: wakemeup on May 20, 2010, 02:57:03 am
Post by: Darth Austrakast on May 20, 2010, 08:01:48 am
What does the "Y" shaped skeletal formula represent? Can someone please provide notes or something on drawing/reading skeletal formula. I have major confusions particularly regarding the branched chain skeletal formulas. And ring/benzenes are not in Unit 1 Syllabus ryt?
no benzenes r not in our syllabus
here are some links http://www.chemguide.co.uk/basicorg/conventions/names.html#top (http://www.chemguide.co.uk/basicorg/conventions/names.html#top)
http://www.chemguide.co.uk/basicorg/conventions/draw.html#top (http://www.chemguide.co.uk/basicorg/conventions/draw.html#top)
hope it helps ;D
Post by: coatseville on May 20, 2010, 12:21:50 pm
Thanks :)
Post by: Igcseboy on May 20, 2010, 12:42:48 pm
For (a) 3 moles of CO2 is formed. And 2 moles of O2 was used to form water. Thus 8 hydrogens were used.
Thus, C3H8
(b) 1 gram of H2 will mean 1 mole of H2. 20 grams of Ne will mean 1 mole of Ne. Thus same number of atoms as Hydrogen.
how did u calculate the moles for a part
and for b hw is moles for H2 1... its is 1/2=0.5 moles :S:S:S
Post by: Darth Austrakast on May 20, 2010, 01:10:30 pm
I was wondering does anyone have good notes of hess's law diagrams?
Thanks :)
http://www.knockhardy.org.uk/assets/ENTH.PDF (http://www.knockhardy.org.uk/assets/ENTH.PDF)
http://www.ausetute.com.au/hesslaw.html (http://www.ausetute.com.au/hesslaw.html)
there u go ;)
Post by: raimunts on May 20, 2010, 03:11:19 pm
In the self-heating cans, the bottom has a compartment containing copper(II) nitrate
solution. When a button on the bottom of the can is pressed, the magnesium powder is
released into the compartment where it reacts with the copper(II) nitrate solution.
(a) A student investigated the enthalpy change for this reaction by measuring
50.0 cm3 of 0.300 mol dm–3 copper(II) nitrate solution into a 100 cm3 beaker and
adding 1g (an excess) of magnesium powder.
The results are shown below.
Temperature of copper(II) nitrate solution at start = 22 C
Temperature of mixture after reaction = 43 C
(i) Calculate the energy change which took place. The specific heat capacity of the
solution is 4.20 J g–1K–1.
Which is the correct value for the energy change in joules?
[6CH01, Specimen Paper]
How to solve this? Answer in mark scheme is 4410 Joules
Post by: Ibiza279 on May 20, 2010, 03:47:06 pm
1. How to form crystals from a solution ?
2. how to form a saturated solution ?
Thanks all ! :)
Post by: Darth Austrakast on May 20, 2010, 03:49:01 pm
density of aq soln=density of water so mass of soln=50cm^3*1gcm^-3=50g
so energy change= m*c*del-theta =50*4.2*(43-22)=4410 J
Post by: Ibiza279 on May 20, 2010, 03:54:28 pm
Mg(s) + Cu(NO3)2(aq) Mg(NO3)2(aq) + Cu(s)
In the self-heating cans, the bottom has a compartment containing copper(II) nitrate
solution. When a button on the bottom of the can is pressed, the magnesium powder is
released into the compartment where it reacts with the copper(II) nitrate solution.
(a) A student investigated the enthalpy change for this reaction by measuring
50.0 cm3 of 0.300 mol dm–3 copper(II) nitrate solution into a 100 cm3 beaker and
adding 1g (an excess) of magnesium powder.
The results are shown below.
Temperature of copper(II) nitrate solution at start = 22 C
Temperature of mixture after reaction = 43 C
(i) Calculate the energy change which took place. The specific heat capacity of the
solution is 4.20 J g–1K–1.
Which is the correct value for the energy change in joules?
[6CH01, Specimen Paper]
How to solve this? Answer in mark scheme is 4410 Joules
dude thats simple, as 50 cm^3 of solution is used, jus do the simple math, 50 X (43 - 22) X 4.2 = 4410
Post by: Darth Austrakast on May 20, 2010, 03:55:30 pm
i want to noe the procedure that we have to write when they ask us for :-
1. How to form crystals from a solution ?
2. how to form a saturated solution ?
Thanks all ! :)
i don't think these are required for unit 1 xams
Post by: Ibiza279 on May 20, 2010, 03:56:09 pm
dude thats simple, as 50 cm^3 of solution is used, jus do the simple math, 50 X (43 - 22) X 4.2 = 4410
oh yh and as the density of water 1g/cm^3, the density is 1 so the mass = volume, so 50 cm^3 = 50g :)
Post by: Ibiza279 on May 20, 2010, 03:57:11 pm
i don't think these are required for unit 1 xams
dude these small experiments are, if u check the latest papers, i mean jan 09 till jan 10, ull find such questions :|
Post by: Darth Austrakast on May 20, 2010, 04:10:47 pm
for saturated solution they will ask for a particular volume of solution so what u need to do is measure the required mass of salt/substance using electronic mass balance and accurately transfer the solid to a volumetric flask.Then add 50cm^3 of distilled water and shake the mixture well to dissolve the solid.Then add distilled water and make the solution up to the mark.
Post by: Ibiza279 on May 20, 2010, 04:17:24 pm
Oh OK i didn't solve the papers yet ;D
for saturated solution they will ask for a particular volume of solution so what u need to do is measure the required mass of salt/substance using electronic mass balance and accurately transfer the solid to a volumetric flask.Then add 50cm^3 of distilled water and shake the mixture well to dissolve the solid.Then add distilled water and make the solution up to the mark.
uh no, wrong, with saturated, they mean that the solution should have the max amount of salt content in it so that no more salt can further b dissolved. for that, in 100 cm3 distill water which is in a beaker, add salt and dissolve it with a glass rod. while dissolving, keep adding excess of salt until no more salt can b dissolved. filter the solution to remove any excess salt, and u hav a saturated salt solution :)
Post by: Kim on May 20, 2010, 04:21:42 pm
i was wondering if u guys have any mcq to study from??
how are you studing for em??
where can i get sum mcq like those in the papers?
Post by: annie_angel on May 20, 2010, 04:24:58 pm
Post by: Darth Austrakast on May 20, 2010, 04:27:57 pm
Post by: Kim on May 20, 2010, 04:35:01 pm
HII KIM!!!!
hey how r ur exams goin???
i have an exam tomorrow
not in the mood
@austrakast--lol i mean is there any where else?
Post by: Darth Austrakast on May 20, 2010, 04:45:34 pm
Post by: Ibiza279 on May 20, 2010, 05:08:28 pm
Post by: raimunts on May 20, 2010, 05:31:25 pm
790, 1600, 3200, 4400, 16100 kJ mol–1
In which group of the Periodic Table is Z found?
A 2
B 3
C 4
D 5
Answer is C 4.
How can you tell?
Post by: Kim on May 20, 2010, 05:35:02 pm
4 The first five ionization energies of an element, Z, are:
790, 1600, 3200, 4400, 16100 kJ mol–1
In which group of the Periodic Table is Z found?
A 2
B 3
C 4
D 5
Answer is C 4.
How can you tell?
u can see in the question dat are 3 jumps
from 790 to1600
1600 to 3200
4400 to 16100
which means it has 4 shells (as one jump means that nxt electron is from another shell closer to the nucleus)
so group 4
do u get it?
Post by: raimunts on May 20, 2010, 05:39:45 pm
Post by: Darth Austrakast on May 20, 2010, 05:39:57 pm
Post by: Darth Austrakast on May 20, 2010, 05:41:47 pm
u can see in the question dat are 3 jumps
from 790 to1600
1600 to 3200
4400 to 16100
which means it has 4 shells (as one jump means that nxt electron is from another shell closer to the nucleus)
so group 4
do u get it?
kim dnt confuse its NOT shells ITS ELECTRONS
Post by: raimunts on May 20, 2010, 05:42:51 pm
Yes cuz after the 4th ionization energy there is a huge jump-the 5th ionization energy corresponds to the 5th electron.Since there is a such a huge gap between 4th and 5th it implies that all the 5th electron removed was from another shell. Group IV elements have 4 electrons on their last shell so it is Group IV
Got it now...4 electrons not shells. Thanx to both..austrkast and kim :)
Post by: Kim on May 20, 2010, 05:43:01 pm
kim dnt confuse its NOT shells ITS ELECTRONS
ok sorry
Post by: Kim on May 20, 2010, 06:00:00 pm
cud sumone help me wid q 18 ai from the sample paper unit 1
why is the energy change 4410 which is half of wat i get??
Post by: Kim on May 20, 2010, 06:04:03 pm
hey
cud sumone help me wid q 18 ai from the sample paper unit 1
why is the energy change 4410 which is half of wat i get??
haha lol no need
i figured it out was using 100 instead of 50
lol so no need
Post by: Igcseboy on May 20, 2010, 06:06:38 pm
any important points???
Post by: Saladin on May 20, 2010, 06:11:09 pm
guys and gals.... so wat r u ppl doin for last hours prep??? :S:S:S
any important points???
Keep doin papaz!
Post by: Kim on May 20, 2010, 06:14:07 pm
guys and gals.... so wat r u ppl doin for last hours prep??? :S:S:S
any important points???
well i am just doin papers
try doin sum old papers
and am going to revise everything in my notes and txtbk
have alot of time in the morn as well so will do revision then as well
Post by: Ibiza279 on May 20, 2010, 06:16:17 pm
guys and gals.... so wat r u ppl doin for last hours prep??? :S:S:S
any important points???
jus do the latest papers, they ll give u the general trend of how the questions are asked and check the corresponding mark schemes to noe how the questions should b answered. :)
Post by: Kim on May 20, 2010, 06:32:19 pm
Post by: Darth Austrakast on May 20, 2010, 06:43:37 pm
thats in U2
Post by: Saladin on May 20, 2010, 06:43:52 pm
do we need to know iodine titrations for tomorrow??
No, thats in Unit 2.
Post by: Igcseboy on May 20, 2010, 06:57:54 pm
well i am just doin papers
try doin sum old papers
and am going to revise everything in my notes and txtbk
have alot of time in the morn as well so will do revision then as well
where r u frm??? which skuul????
Post by: Kim on May 20, 2010, 06:59:05 pm
where r u frm??? which skuul????
why????
i am living in dubai
Post by: Igcseboy on May 20, 2010, 07:03:31 pm
Post by: Kim on May 20, 2010, 07:05:29 pm
just askin am frm KSA...... i have paper like 3:30 pm so am realxed for now ... wat abt u???
oooh i have at 3.30 as well
but u r an hour behind my time i think
so it will be at ur 2.30
Post by: Igcseboy on May 20, 2010, 07:14:36 pm
oooh i have at 3.30 as well
but u r an hour behind my time i think
so it will be at ur 2.30
yup!!!!
hey do we have to do the alcohol and aloalkane organic chemistry??
and wat abt CFCs and ozone?? :S:S
Post by: Kim on May 20, 2010, 07:17:18 pm
yup!!!!
hey do we have to do the alcohol and aloalkane organic chemistry??
and wat abt CFCs and ozone?? :S:S
well i learned the whole of unit and unit 2
well cfc and ozone usually is for unit 2
i think u just need to know the side effect of polymers and their advantages
but just read the others as well
better be safe then sorry
so where do u live in ksa?
Post by: Kim on May 20, 2010, 07:20:01 pm
jan 2008 unit 1 q 4bi
how do u get 2e ?
Post by: Igcseboy on May 20, 2010, 07:29:29 pm
i have another question
jan 2008 unit 1 q 4bi
how do u get 2e ?
as it form Cl2 molecules so 2e as "Cl2" ... get it???
am live in riyadh well am basically frm Pakistan... settled here...
By the way redox reactions are not in Unit 1 :S:S :D
Post by: Kim on May 20, 2010, 07:31:34 pm
as it form Cl2 molecules so 2e as "Cl2" ... get it???
am live in riyadh well am basically frm Pakistan... settled here...
By the way redox reactions are not in Unit 1 :S:S :D
really??thanks
oooh cool
then u shud come join us in the pakistanis hea group if u havent already been there
Post by: Igcseboy on May 20, 2010, 07:36:26 pm
really??thanks
oooh cool
then u shud come join us in the pakistanis hea group if u havent already been there
sure i will ..... so u also from Pakistan ?? which city??
By the way a question which has the higher melting point Neon or Krypton??
and why does melting point increases from sodium to aluminium??
Post by: Kim on May 20, 2010, 07:40:07 pm
sure i will ..... so u also from Pakistan ?? which city??
By the way a question which has the higher melting point Neon or Krypton??
and why does melting point increases from sodium to aluminium??
yup i m from lahore
krypton has the higher boiling point
although they both have dispersion forces krypton has more electrons so the dispersion forces are stronger in krypton
and the mp increases from sodium to aluminium because across a period the radius decreases
and the nuclear charge increases so the outer electron experiences more attraction thus is harder to remove
Post by: Igcseboy on May 20, 2010, 07:43:01 pm
yup i m from lahore
krypton has the higher boiling point
although they both have dispersion forces krypton has more electrons so the dispersion forces are stronger in krypton
and the mp increases from sodium to aluminium because across a period the radius decreases
and the nuclear charge increases so the outer electron experiences more attraction thus is harder to remove
ahan i am frm Karachi
but shud it not be Neon as it has less electron shells so it is strongly attracted to the nucleus:S:S
Post by: Kim on May 20, 2010, 07:46:20 pm
ahan i am frm Karachi
but shud it not be Neon as it has less electron shells so it is strongly attracted to the nucleus:S:S
cool nnice place
i think its krypton because they said boiling point and wenever it is boiling point u have to describe the intermolecular forces
Post by: Kim on May 20, 2010, 07:47:58 pm
Post by: vanibharutham on May 20, 2010, 07:49:34 pm
neon has a higher ionization energy becasuse force of attractio between nucleus and electrons is much more...but krypton has a much higher boiling point because of the IM forces involved - it has many more and stronger vdw forces than neon and so higher boiling point
Post by: Igcseboy on May 20, 2010, 07:52:33 pm
boiling poitn shouldnt be confused with Ioinisation energy
neon has a higher ionization energy becasuse force of attractio between nucleus and electrons is much more...but krypton has a much higher boiling point because of the IM forces involved - it has many more and stronger vdw forces than neon and so higher boiling point
ok thanxx aloot!! :)
so whenever it boliling or melting points we will consider IM force rite ????
Post by: Kim on May 20, 2010, 07:55:14 pm
ok thanxx aloot!! :)
so whenever it boliling or melting points we will consider IM force rite ????
only for boiling point
Post by: Igcseboy on May 20, 2010, 07:56:58 pm
only for boiling point
and melting point??
Post by: Igcseboy on May 20, 2010, 07:59:44 pm
Post by: Kim on May 20, 2010, 08:10:41 pm
shudnt boron have a higher bp then na???
Post by: vanibharutham on May 20, 2010, 08:11:05 pm
BCl3 covalent with only weaker Im forces
Post by: Kim on May 20, 2010, 08:12:44 pm
NaCl ionic
BCl3 covalent with only weaker Im forces
isnt boron a metal??
Post by: vanibharutham on May 20, 2010, 08:13:46 pm
Post by: Kim on May 20, 2010, 08:14:36 pm
BCl3 is still covalent compound
ok thanks
Post by: vanibharutham on May 20, 2010, 08:19:25 pm
Post by: Igcseboy on May 20, 2010, 08:20:27 pm
any other doubts ppl?
if we have to compare melting points how will we ????
Post by: vanibharutham on May 20, 2010, 08:28:07 pm
just think off types of bonds
ionic bonds, metallic bonds, intermolecular forces, covalent bonds etc
Post by: Igcseboy on May 20, 2010, 08:32:59 pm
doubt you will have to worry about that in Unit 1
just think off types of bonds
ionic bonds, metallic bonds, intermolecular forces, covalent bonds etc
i didnt get ur first sentence but the rest i got it thanxxx
Post by: Meticulous on May 20, 2010, 08:44:20 pm
Post by: Kim on May 20, 2010, 08:56:07 pm
What's the difference between thermodynamic and kinetic stability?
although u dont need it for unit 1 but ill tell ya
kinetic stability is wen the activation energy is very high and the number of colliding particles that possess that energy is very less so the reaction will not take place.this type of system is called as kinetically stable
thermodynamic stabilty is wen the reaction is very exothermic and so will take place as heat is given out
the products are said to be thermodynamically stable
Post by: raimunts on May 20, 2010, 09:17:20 pm
Post by: Kim on May 20, 2010, 09:22:26 pm
hello. are polar and non-polar molecules in Unit 1 syllabus? Can someone please briefly explain them if they are.
well they are not there
polar molecule- is a molecule where the bonded electrons are shared unequally.the bonded atoms are different wid different electronegativities
non polar-is a molecule where the bonded electrons are shared equally.bonded atoms are the same wid same electronegativities
all assymetrical molecules are polar
in symmetrical molecules the dipoles cancel each other out so the molecule is non polar
Post by: raimunts on May 20, 2010, 09:30:08 pm
Post by: Kim on May 20, 2010, 09:32:40 pm
Post by: raimunts on May 20, 2010, 09:52:52 pm
While applying Hess's law, why is H1= 2*H2 - H3 [why is H2 multiplied by 2?]
Post by: Kim on May 20, 2010, 09:57:50 pm
6CH01, JAN 2009, Q. 23 (bi)
While applying Hess's law, why is H1= 2*H2 - H3 [why is H2 multiplied by 2?]
because there are 2 moles of KHCO3
Post by: raimunts on May 20, 2010, 10:06:30 pm
because there are 2 moles of KHCO3thanx! uv answered about 6 questions of mine just tonight [and prolly many more to come]...i owe my chemistry A (hopefully A) to this site nd u ppl!
Post by: raimunts on May 20, 2010, 10:33:36 pm
temperature and pressure?
[Relative atomic masses: H = 1; C = 12; O = 16; F = 19; Ne = 20]
A 1 gram of ethane
B 1 gram of oxygen
C 1 gram of fluorine
D 1 gram of neon
Answer in mark scheme is D. Neon. Isn't Number of moles = Mass/Molar mass, and more moles mean greater volume, so shouldnt Oxygen having least Molar mass occupy greatest volume>
Post by: raimunts on May 20, 2010, 10:35:10 pm
Post by: Meticulous on May 20, 2010, 10:36:05 pm
mol= mass/Ar...and take care Ar of oxygen is 32, not 16.
then multiply the mole by 24 dm3
Post by: Meticulous on May 20, 2010, 10:36:39 pm
Post by: raimunts on May 20, 2010, 11:19:56 pm
given below. Which will occur in a mass spectrum of chlorine gas, Cl2, from an ion
with a single positive charge?
A 35.5
B 36
C 71
D 72
Any idea?
Post by: raimunts on May 20, 2010, 11:23:28 pm
following shows the number of iodine atoms in 0.025 g of I2?
The Avogadro constant is 6.02 × 1023 mol–1.
0.025
× 6.02 × 1023
A
126.9
0.025
× 6.02 × 1023
B
253.8
253.8
× 6.02 × 1023
C
0.025
126.9
× 6.02 × 1023
D
0.025
6PH01. Jan 2010 Q.2 and Q.3. The mark scheme answers seem weird
Post by: Meticulous on May 21, 2010, 07:14:37 am
mass/mr of iodine molecules,
the multiply by 2 because there are 2 iodine atoms in each mole.
the 2 cancels out with the Mr.
Post by: Uchia on May 21, 2010, 07:32:06 am
the possible peaks on the mass spectrometer would be (Cl35 Cl35)+, (Cl37 Cl37)+, (Cl35 Cl37)+ well calculate the mr and see which one is given
35+35 = 70
37+37 =74
35 + 37 =72
so 72 is the right answer
Post by: raimunts on May 21, 2010, 07:54:25 am
first you find the number of moles:
mass/mr of iodine molecules,
the multiply by 2 because there are 2 iodine atoms in each mole.
the 2 cancels out with the Mr.
What do you mean by the 2 cancels out with the Mr? This is the calculation I made:
(0.025/126.9) * 2 * Avogadro's constant
How does the 2 get divided?
Post by: Kim on May 21, 2010, 08:15:06 am
What do you mean by the 2 cancels out with the Mr? This is the calculation I made:
(0.025/126.9) * 2 * Avogadro's constant
How does the 2 get divided?
i dont get it why are u guys multiplying by 2????
there is no 2 in the question
Post by: Dento on May 21, 2010, 08:53:16 am
Post by: Kim on May 21, 2010, 08:58:28 am
are halogenoalkanes and their reactions in unit 1? or in unit 1 organic we must only know about alkanes, alkenes, alcohols, etc
in unit 1 organic u only need to know about alkanes alkenes and alcohols
Post by: Dento on May 21, 2010, 08:59:11 am
Post by: Kim on May 21, 2010, 09:00:53 am
thanks kim, i appreciate the early reply on such an early morning, ;0
its not early
its 12 in the afternoon where i am
Post by: Dento on May 21, 2010, 09:02:16 am
Post by: Ibiza279 on May 21, 2010, 09:06:32 am
Post by: Kim on May 21, 2010, 09:07:19 am
well its 11 here so i thought chemistry students might be sleeping as unit 1 is today PM timing
haha nice
i have to leave in about 2 and half hours
so wont sleep
Post by: Kim on May 21, 2010, 09:09:56 am
i don't get Raimunts post about the iodine atoms question, i mean Iodine exists as I2 rite, but when u see the mark scheme, if u multiply 126.9 X 2, ur doin it the wrong way, can some one explain it to me plz, the logic me n a buddy of mine made of it was that Iodine exists as a mono atomic substance in the body as part of some compound so it would exist as an Ion, so v use only 126.9, can some one enlighten me plzzz !!!!! :(
well wat i think because they say to find the no of atoms so u divide the moles by the mass of an iodine atom and then multiply by the avogadro constant to get the no of atoms
Post by: Ibiza279 on May 21, 2010, 09:14:10 am
well wat i think because they say to find the no of atoms so u divide the moles by the mass of an iodine atom and then multiply by the avogadro constant to get the no of atoms
but then as u say it in the Volume question in which flourine is used, why do v take its mass number X 2 while here we jus take the mass number ???? ???
Post by: Kim on May 21, 2010, 09:15:11 am
but then as u say it in the Volume question in which flourine is used, why do v take its mass number X 2 while here we jus take the mass number ???? ???which question is dat???
Post by: Ibiza279 on May 21, 2010, 09:28:22 am
which question is dat???
its one of Raimunts posts, a page bak, also one of the mcqs of June 09, 17th i think.
Post by: Kim on May 21, 2010, 09:32:45 am
its one of Raimunts posts, a page bak, also one of the mcqs of June 09, 17th i think.
that is adifferent question u have to calculate tyhe volume for dat so u calculate using f2
but for this u r calculating atoms and in the periodic table the masses are of atoms so u directly use dat mass
Post by: Ibiza279 on May 21, 2010, 09:35:11 am
Post by: Ibiza279 on May 21, 2010, 09:36:14 am
that is adifferent question u have to calculate tyhe volume for dat so u calculate using f2
but for this u r calculating atoms and in the periodic table the masses are of atoms so u directly use dat mass
ohhh, so for mass of atoms, v use the single value of Mr, but for calculating the volume, we take the mass of the molecule, rite ??? :D
Post by: Kim on May 21, 2010, 09:43:12 am
also, could u tell me the trends in solubility of the group 1 and 2 metals, also the trend relating to the hydration enthalpy and lattice enthalpy and its explanation plz :D
ok solubility of group 2 hydroxides increses down the group
solubility of group 2 sulphates decreases down the group
group 1 metals solubility increases down the group
and yes(for the the above post)
i am sorry i dont know about lattice and hydration enthalpy
Post by: Ibiza279 on May 21, 2010, 09:44:47 am
ok solubility of group 2 hydroxides increses down the group
solubility of group 2 sulphates decreases down the group
group 1 metals solubility increases down the group
and yes(for the the above post)
i am sorry i dont know about lattice and hydration enthalpy
so group 1 metals solubility increases down the group for both hydroxides AND sulphates or wat ?
Post by: Kim on May 21, 2010, 09:46:18 am
so group 1 metals solubility increases down the group for both hydroxides AND sulphates or wat ?
[/quote/]
yes
Post by: Ibiza279 on May 21, 2010, 09:59:54 am
so group 1 metals solubility increases down the group for both hydroxides AND sulphates or wat ?
[/quote/]
yes
ahh Thanks alot yara, that helped alot, well im off fer Jummah Namaz ;D cya !
Post by: Kim on May 21, 2010, 10:01:27 am
ahh Thanks alot yara, that helped alot, well im off fer Jummah Namaz ;D cya !
no problem
Post by: Summer :] on May 21, 2010, 11:59:57 am
NaCl ionic
BCl3 covalent with only weaker Im forces
BCL3 has covalent bonds - because born is polarising so it pulls the electrons of the anion towards it distorting/causing the bond to be changed..so it becomes partially ionic and covalent though it's properties are mostly covalent
NaCL - is ionic, opposite charges, more attaction, higher boiling points..
Post by: wakemeup on May 21, 2010, 12:05:25 pm
Post by: Igcseboy on May 21, 2010, 04:07:31 pm
From my point of view it was easy :):):)
wat abt othersss
Post by: Darth Austrakast on May 21, 2010, 05:36:59 pm
though messed up in 1 mcq and not sure about 1 mark............but thank God for no freaky questions!
Post by: Igcseboy on May 21, 2010, 05:42:48 pm
it was good
though messed up in 1 mcq and not sure about 1 mark............but thank God for no freaky questions!
ya Thank God no freaky things :P
Post by: Kim on May 21, 2010, 07:31:18 pm
ya Thank God no freaky things :P
yay same here i was soo glad wen i saw the paper
Post by: wakemeup on May 21, 2010, 07:42:09 pm
So how was the paper!!!!!!!
From my point of view it was easy :):):)
wat abt othersss
I'm not really satisfied. I kinda messed up in some really easy q's, like that ppm thing and the peaks of Br2 ions q. It wasn't as bad as it could've been but eh... :-\
Post by: Uchia on May 21, 2010, 07:51:11 pm
Post by: Kim on May 21, 2010, 07:51:51 pm
I'm not really satisfied. I kinda messed up in some really easy q's, like that ppm thing and the peaks of Br2 ions q. It wasn't as bad as it could've been but eh... :-\
hey dont worry i am sure u will totally ace it
Post by: Blizz_rb93 on May 21, 2010, 08:19:43 pm
anyways... i think i messed up on unit 1 :( it was pretty hard in my opinion, didn't expect it like this..
and then u got unit 3 which was HARD!!! :/
and now my only chance of getting a decent grade overall is acing unit 2 :/
fml
Post by: Saladin on May 21, 2010, 08:22:49 pm
well i have to renew what i said -__-'
anyways... i think i messed up on unit 1 :( it was pretty hard in my opinion, didn't expect it like this..
and then u got unit 3 which was HARD!!! :/
and now my only chance of getting a decent grade overall is acing unit 2 :/
fml
iA.
Post by: Kim on May 21, 2010, 08:26:51 pm
well i have to renew what i said -__-'
anyways... i think i messed up on unit 1 :( it was pretty hard in my opinion, didn't expect it like this..
and then u got unit 3 which was HARD!!! :/
and now my only chance of getting a decent grade overall is acing unit 2 :/
fml
dont worry IA u will do amazing
i will pray for you
dont worry hope is not over pppl think they did bad but then they find out that they actually did good so dont worry
stop thinking about it and prepare for ur nxt paper
Post by: Saladin on May 21, 2010, 08:30:13 pm
well i have to renew what i said -__-'
anyways... i think i messed up on unit 1 :( it was pretty hard in my opinion, didn't expect it like this..
and then u got unit 3 which was HARD!!! :/
and now my only chance of getting a decent grade overall is acing unit 2 :/
fml
Let it go man!
I believe in you!
Post by: Blizz_rb93 on May 21, 2010, 08:31:32 pm
inshallah ill do good on the next paper
right now im preparing for the bio unit 1 and c1 and s1, inshallah i get good grades
<3
Post by: Kim on May 21, 2010, 08:32:45 pm
thanks everyone!! really appreciate it
inshallah ill do good on the next paper
right now im preparing for the bio unit 1 and c1 and s1, inshallah i get good grades
<3
IA
hey i ahvebio 1 as well cool
Post by: Blizz_rb93 on May 21, 2010, 08:41:13 pm
IA
hey i ahvebio 1 as well cool
inshallah we both do good =] if u need any help on anything in bio u can pm me, im pretty good in bio unit 1 xD
Post by: Kim on May 21, 2010, 08:42:51 pm
Post by: Dento on May 22, 2010, 02:53:31 pm
so can anyone tell me the answr for the Br2 peaks and the ppm question?
Post by: Saladin on May 22, 2010, 02:54:19 pm
ok 24 hours passed,
so can anyone tell me the answr for the Br2 peaks and the ppm question?
3 peaks.
Post by: Dento on May 22, 2010, 02:55:52 pm
3 peaks which is br79-br79, br79-br81, br81-81 ryt ?
and about the ppm,
is it we multiply the 0.100 mol by 40, then divide by 1 million and then multiply it with 1 kg ?
Post by: Saladin on May 22, 2010, 03:04:35 pm
ok perfect,
3 peaks which is br79-br79, br79-br81, br81-81 ryt ?
and about the ppm,
is it we multiply the 0.100 mol by 40, then divide by 1 million and then multiply it with 1 kg ?
i got 4 ppm.
Post by: raimunts on May 23, 2010, 05:41:13 pm
Post by: Saladin on May 23, 2010, 07:13:28 pm
i got 4000 ppm
that is wayyy toooo high!!!!
Post by: Meticulous on May 29, 2010, 07:03:25 pm
i got 4000 ppm
Ditto! And I am sure it was right ;)
Post by: Igcseboy on May 30, 2010, 08:16:58 am
Ditto! And I am sure it was right ;)
same here... and am pretty confident abt it .. :)
Post by: Darth Austrakast on May 30, 2010, 11:30:20 am
Post by: Meticulous on May 30, 2010, 11:33:23 am
i got 400ppm most people in our center gt this value ???
You had to change cm3 todm3 or the opposite
Post by: Sweet_03 on May 30, 2010, 02:43:27 pm
other than 2009 & 2010
i REALY NEED some practice
Post by: Meticulous on May 30, 2010, 02:46:26 pm
Post by: Kim on May 30, 2010, 03:40:33 pm
Guys what papers can we do for unit 2 ?
other than 2009 & 2010
i REALY NEED some practice
do all the old unit 2 papers
it will help u realize where u stand
and u will learn how to answer the questions in the paper
questions are usually repeated so do as many as u can
8)
Post by: Igcseboy on May 30, 2010, 05:08:57 pm
do all the old unit 2 papers
it will help u realize where u stand
and u will learn how to answer the questions in the paper
questions are usually repeated so do as many as u can
8)
repeated wat do u mean??? i dont think so they r repeated :S
Post by: Meticulous on May 30, 2010, 05:14:37 pm
repeated wat do u mean??? i dont think so they r repeated :S
All questions from the new syllabus are repeated from the old syllabus ;)
Plus, I strongly advice you to STUDY the new past papers, not just doing them. Observe what's new they didn't include, etc..
Post by: Kim on May 30, 2010, 05:27:36 pm
repeated wat do u mean??? i dont think so they r repeated :S
yup they are
for my bio paper the questions were repeated
so do as many as u can
and yes see wat is not included in the sp and jan 2010 pp there is a high chance it will be in this yrs paper
Post by: Igcseboy on May 30, 2010, 05:32:01 pm
any1 has some notes on periodic table?????
Post by: Kim on May 30, 2010, 05:33:08 pm
ok thankss
any1 has some notes on periodic table?????
well there is a thread where nid included notes on periodic table
i think its called AS chemistry notes
Post by: Igcseboy on May 30, 2010, 05:57:48 pm
well there is a thread where nid included notes on periodic table
i think its called AS chemistry notes
ok thankss
is there any evidence to show tht old syllabus questions are repeated :D
and r physics also repeated??
Post by: Meticulous on May 30, 2010, 05:59:11 pm
ok thankss
is there any evidence to show tht old syllabus questions are repeated :D
and r physics also repeated??
No. Trust me!
Post by: Kim on May 30, 2010, 06:00:38 pm
ok thankss
is there any evidence to show tht old syllabus questions are repeated :D
and r physics also repeated??
well the only proof u can get is so sum pp the questions come again and again
do u take bio??
Post by: Sweet_03 on May 30, 2010, 06:01:06 pm
+ for unit 2 .. is the question only from the old paper 2 ? or is it even from the old paper 1 ?
Post by: Meticulous on May 30, 2010, 06:02:58 pm
but i find the old paper 2 questions easier =/
+ for unit 2 .. is the question only from the old paper 2 ? or is it even from the old paper 1 ?
Paper 1 and 2
Post by: Igcseboy on May 30, 2010, 06:06:18 pm
well the only proof u can get is so sum pp the questions come again and again
do u take bio??
nopee
Post by: Kim on May 30, 2010, 06:11:39 pm
nopee
well then cant give ya proof
Post by: Igcseboy on May 30, 2010, 06:13:23 pm
Post by: Igcseboy on May 30, 2010, 06:15:36 pm
Post by: Meticulous on May 30, 2010, 06:17:24 pm
polypropene does not have a sharp melting temperature but softens over a range of temperatures suggest why this is so??
Because it is not pure. An impure substance melts or boils over a temperature range.
Post by: Uchia on May 30, 2010, 09:23:38 pm
Post by: Saladin on May 30, 2010, 09:38:08 pm
Because it is not pure. An impure substance melts or boils over a temperature range.
That is not true actually, it is because there are many varying chain lengths in the substance. This is the answer in the mark-scheme.
Post by: Blizz_rb93 on May 31, 2010, 02:03:37 pm
thank you!!
Post by: Saladin on May 31, 2010, 02:05:51 pm
I would advise you to go there.
Post by: Blizz_rb93 on May 31, 2010, 02:09:53 pm
Chemguide (http://www.chemguide.co.uk/) is the best place to learn pretty much anything in chemistry.okay im checking it out now, thank you! :)
I would advise you to go there.
Post by: Sweet_03 on May 31, 2010, 03:01:42 pm
the Answer for Question 3 (a)(ii)
it says:
electrons promoted (by heat/flame to a higher level) (1)
NOT electrons excited
fall back down/return (1)
emit light (1)
wait wats [NOT electrons excited] ??
ive always learned it as EXCITED ! isnt thst right ? ???
Post by: Kim on May 31, 2010, 03:04:33 pm
Guys , if you check Unit 1 June 2006 Markscheme ..
the Answer for Question 3 (a)(ii)
it says:
electrons promoted (by heat/flame to a higher level) (1)
NOT electrons excited
fall back down/return (1)
emit light (1)
wait wats [NOT electrons excited] ??
ive always learned it as EXCITED ! isnt thst right ? ???
wat they want u to write is dat electrons are promoted to higher energy levels by heating
do not write electrons are excited
Post by: Saladin on June 03, 2010, 06:33:45 pm
But I believe that 10a) should be B.
And 10b) should be D.
But I simply do not get this.
Post by: Meticulous on June 03, 2010, 07:48:15 pm
The forward reaction is exothermic. Therefore, increasing the temperature will counteract this change, shifting to the endothermic side. (Left hand side|). An important point to notice is that when talking about yield, we ALWAYS mean the product. Therefore the yield will decrease.
And we know that increasing the temperature increase the reaction rate.
Therefore the answer is A
Clear?
Post by: Meticulous on June 03, 2010, 07:52:40 pm
I know what is your mistake. You counted the number of moles of ALL the reactants. Wrong!
Pressure ONLY affects GASEOUS molecules. It has NO effect on solids.
LHS: 3 moles RHS: 2 moles
Therefore, decreasing pressure will shift equilibrium to left, decreasing the product yield.
Clear?
Post by: Saladin on June 03, 2010, 08:11:55 pm
10b)
I know what is your mistake. You counted the number of moles of ALL the reactants. Wrong!
Pressure ONLY affects GASEOUS molecules. It has NO effect on solids.
LHS: 3 moles RHS: 2 moles
Therefore, decreasing pressure will shift equilibrium to left, decreasing the product yield.
Clear?
Correction, sulphur is a solid. You do not count that.
Post by: Meticulous on June 03, 2010, 08:13:15 pm
Correction, sulphur is a solid. You do not count that.
Exactly, thats what I just said. On the right, there are only 2 moles. You don't count the sulpher.
Post by: Saladin on June 03, 2010, 08:15:07 pm
Exactly, thats what I just said. On the right, there are only 2 moles. You don't count the sulpher.
oopsies, my bad, i was thinking it was more pressure! :P
Silly me.
but wat abt a?
Post by: Meticulous on June 03, 2010, 08:15:56 pm
For a, check the previous page.
Post by: Saladin on June 03, 2010, 08:17:39 pm
LOL..its alright.
For a, check the previous page.
Now I just feel like smacking my head now. Whenever I see negative, I think of endothermic! LOL
Sorry for the inconvenience.
Post by: Meticulous on June 03, 2010, 08:20:33 pm
Just as soon as you see delta h is negative, put the word exo on the forward, and endo on the backward reaction.
That way you wont get confused.
Post by: Summer :] on June 04, 2010, 01:11:28 pm
O2 --> O. + O. (Reaction 1)
O. + O2 --> O3 (Reaction 2)
The ozone absorbs ultraviolet radiation and breaks down to oxygen molecules and atoms.
O3 --> O2 + O. (Reaction 3)
Another reaction, which is not light dependent, also removes ozone:
O3 + O. --> 2O2 (Reaction 4)
Over time ozone and oxygen concentrations reach a steady state.
Question is: Reaction 2 has an enthalpy change of -100 kj mol-1 and Reaction 4 an enthalpy change of -390 kg mol-1. Assuming that Reactions 1 and 2 are followed by Reaction 4, show how this results in the upper atmosphere warming up by effectively converting light energy into heat energy.
Calculate the amount of heat produced per mole of oxygen molecules
???
Post by: Saladin on June 04, 2010, 10:58:23 pm
There is a considerable concern about the depletion of the 'ozone layer'. Ozone, 03, is constantly being formed in the upper atmosphere by oxygen molecules reacting with oxygen atoms. These atoms are formed when other oxygen molecules absorb high energy Ultraviolet radiation and undergo homolytic bond fission
O2 --> O. + O. (Reaction 1)
O. + O2 --> O3 (Reaction 2)
The ozone absorbs ultraviolet radiation and breaks down to oxygen molecules and atoms.
O3 --> O2 + O. (Reaction 3)
Another reaction, which is not light dependent, also removes ozone:
O3 + O. --> 2O2 (Reaction 4)
Over time ozone and oxygen concentrations reach a steady state.
Question is: Reaction 2 has an enthalpy change of -100 kj mol-1 and Reaction 4 an enthalpy change of -390 kg mol-1. Assuming that Reactions 1 and 2 are followed by Reaction 4, show how this results in the upper atmosphere warming up by effectively converting light energy into heat energy.
Calculate the amount of heat produced per mole of oxygen molecules
???
Where did u get this from?
Post by: GodOfWar on June 05, 2010, 08:22:23 pm
There is a considerable concern about the depletion of the 'ozone layer'. Ozone, 03, is constantly being formed in the upper atmosphere by oxygen molecules reacting with oxygen atoms. These atoms are formed when other oxygen molecules absorb high energy Ultraviolet radiation and undergo homolytic bond fission
O2 --> O. + O. (Reaction 1)
O. + O2 --> O3 (Reaction 2)
The ozone absorbs ultraviolet radiation and breaks down to oxygen molecules and atoms.
O3 --> O2 + O. (Reaction 3)
Another reaction, which is not light dependent, also removes ozone:
O3 + O. --> 2O2 (Reaction 4)
Over time ozone and oxygen concentrations reach a steady state.
Question is: Reaction 2 has an enthalpy change of -100 kj mol-1 and Reaction 4 an enthalpy change of -390 kg mol-1. Assuming that Reactions 1 and 2 are followed by Reaction 4, show how this results in the upper atmosphere warming up by effectively converting light energy into heat energy.
Calculate the amount of heat produced per mole of oxygen molecules
???
Hmmm... i don't get it ???
Post by: Kim on June 05, 2010, 08:24:20 pm
Post by: studz on June 06, 2010, 12:26:21 am
i know about it to some extent..but its not that clear to me..!
Post by: leebux101 on June 06, 2010, 12:45:11 am
Post by: wakemeup on June 06, 2010, 02:42:15 am
Post by: leebux101 on June 06, 2010, 09:32:28 am
Post by: 3bood on June 06, 2010, 09:57:31 am
as we go down group 2 , cation size increase => polarising power of anion decreases => bonds in nitrates and carbonates are less easily broken => nore difficult to decompose => themal stability of nitrates and carbonates of group 2 increases
hope we all do good in the exam :)
Post by: studz on June 06, 2010, 10:39:24 am
This might be a little difficult to explain but I'll try. Here's the thing, as you go down the group, the polarisation power decreases. Now, you're probably thinking 'That should make the bond weaker'. But the deal is that carbonates and nitrates are not single atoms. The more polarised they are, the more uneven charge density they have because the cation is mainly pulling just one oxygen atom towards itself. This makes the other part of the carbonate or nitrate ion unwilling to stay with the cation. The more you go down group 2, the more the charge density becomes even around the carbonate or nitrate ion as it is less polarised and the ion is more willing to stay with the cation. So as you go down the group metal carbonates and nitrates become more stable. Hope my explanation didn't confuse you too much.
lol i did get confused a bit..but yeah that helped..so thnaks bro..
well also we need to think about the other possible factors too right..like the atomic radii...lattice and hydration enthalpies...
if the attraction is large( atomic radius is less) then a lot of energy will be given out when the lattice is formed from the ions and so the lattice energy wil have a large -ve value..
as we go down the group the value becomes positive..
the lattice energies also fall at diffrnt rates..like for eg: oxide ion is smaller than carbonate ion so its lattice enthalpy will fall faster...
so basically this is the thing right..that as u go down the group..the lattice enthalpy becomes more positive so a great deal of energy is needed to break it down(decompose) n so its stable.. ???
and oh yeah whts with those exceptions everywhere lithium carbonate na dlithium nitrate... ???
thanks alot bro!
Post by: studz on June 06, 2010, 10:42:14 am
Post by: Sweet_03 on June 06, 2010, 10:42:14 am
Post by: Meticulous on June 06, 2010, 11:30:29 am
guys , where can i find Unit2 jan2010 mark scheme ?
Here you go
Post by: Meticulous on June 06, 2010, 11:38:31 am
and can somebody tell me about the hydroxides too...? or it has the same explanation too ??? ???
Same
Post by: wakemeup on June 06, 2010, 12:31:46 pm
lol i did get confused a bit..but yeah that helped..so thnaks bro..There are other factors to consider too but according to the specification, we're only supposed to think in terms of the size and charge of the ions involved i.e polarisation. I've seen the mark schemes and the answers are only given in terms of polarisation too. Anyways, good luck to you and everyone else who's attempting this nightmare.
well also we need to think about the other possible factors too right..like the atomic radii...lattice and hydration enthalpies...
if the attraction is large( atomic radius is less) then a lot of energy will be given out when the lattice is formed from the ions and so the lattice energy wil have a large -ve value..
as we go down the group the value becomes positive..
the lattice energies also fall at diffrnt rates..like for eg: oxide ion is smaller than carbonate ion so its lattice enthalpy will fall faster...
so basically this is the thing right..that as u go down the group..the lattice enthalpy becomes more positive so a great deal of energy is needed to break it down(decompose) n so its stable.. ???
and oh yeah whts with those exceptions everywhere lithium carbonate na dlithium nitrate... ???
thanks alot bro!
Post by: Sweet_03 on June 06, 2010, 12:38:51 pm
Post by: Uchia on June 06, 2010, 01:35:31 pm
open the following site and solve the multiple choice tests they will help u a bit
www.knockhardy.org.uk
salam
Post by: studz on June 06, 2010, 01:45:08 pm
Post by: Darth Austrakast on June 06, 2010, 02:24:58 pm
Post by: studz on June 06, 2010, 07:23:10 pm
i need help with the boiling points across the periods..
fro eg we consider the period 3 elements...
we have sodium magnesium aluminum silicon phosphorous sulfur chlorine and argon...so what is the boiling point trend for these elements..
i need explanation with a reason justifying your choice..
anyone...pleaseee!!!! :(
thankss!
Post by: Kim on June 06, 2010, 08:26:39 pm
i dont get it
Post by: coatseville on June 06, 2010, 08:40:11 pm
Because it says to round to 2dp its actually the 3rd dp that makes the difference because it basically decides if the 2nd is rounded or not..
thats why you do 0.005 x 2 / the number x 100
Hope that makes sense!
Post by: Kim on June 06, 2010, 08:42:35 pm
Yeah :)
Because it says to round to 2dp its actually the 3rd dp that makes the difference because it basically decides if the 2nd is rounded or not..
thats why you do 0.005 x 2 / the number x 100
Hope that makes sense!
ok i am a little slow today so cud u explain where 0.005 and 2 came from??
sorry for the trouble
Post by: coatseville on June 06, 2010, 08:45:53 pm
idk if im explaining tht well its quite hard to explain but yah.. :)
Post by: Kim on June 06, 2010, 08:49:00 pm
no problem the x2 is because the error could have either resulted in the value moving above or below the figure we were given so we have to take that into account and the .5 is because it is always the way we determine if we round a number or not. but the x2 and the .5 is used in all of the % error questions its just the number of dp's (ie 0.005 or 0.5) that changes...
idk if im explaining tht well its quite hard to explain but yah.. :)
ok i get .5 part
but correct me if i am wrong so we are gonna use 2 in all the questions??or does it change?
Post by: Kim on June 06, 2010, 08:59:35 pm
Post by: ksitna on June 06, 2010, 09:08:22 pm
hey u there???
lol im sorry but tht made me llaugh :P
and i need help with tht on too :(
Post by: Kim on June 06, 2010, 09:09:40 pm
lol im sorry but tht made me llaugh :P
and i need help with tht on too :(
glad i cud make u laugh
hahahaa join the club
i only understood the 0.5 part and i just wanna if we always use 2
but apprently that persons gone poof
Post by: Uchia on June 06, 2010, 09:18:10 pm
i'll help a bit
in all the percentage error questions u use the 0.05 ( it could be 0.005 it depends on the question but the june 09 question said to 2 dp so take 0.05)
0.05*2 u should always multiply by 2 just like what the previous fellow said and then u divide by orginal * 100 to get percentage
Post by: Kim on June 06, 2010, 09:21:07 pm
hey
i'll help a bit
in all the percentage error questions u use the 0.05 ( it could be 0.005 it depends on the question but the june 09 question said to 2 dp so take 0.05)
0.05*2 u should always multiply by 2 just like what the previous fellow said and then u divide by orginal * 100 to get percentage
ok thanks in the ms it says u multiply by 0.005
Post by: Uchia on June 06, 2010, 09:21:41 pm
Post by: Kim on June 06, 2010, 09:22:54 pm
sometimes in the question itself they give u the percentage error so no need to use the 0.***5 cz as u should know specific/different apparatus have different accuracy
ok thank you dude u really helped
Post by: Uchia on June 06, 2010, 09:30:26 pm
Post by: Sweet_03 on June 06, 2010, 09:33:05 pm
Post by: Uchia on June 06, 2010, 09:37:25 pm
Post by: GodOfWar on June 06, 2010, 09:43:37 pm
hey guys , can someone pls explain the rate of reactions of the halogenalkanes (primary, secondary, tertiary) .. which one is the fastest/slowest .. and why ? :")
Are u talkig abt elimination or substitution reactions?
Post by: Uchia on June 06, 2010, 09:48:37 pm
well as i could think of
tertiary reacts by SN1 involves 2 steps
Secondary could go both
Primary reacts by SN2 invloves 1 step
as u know SN1 is faster so tertiary is faster if i found more convincing explanation i'll tell u as soon as possible
Post by: Darth Austrakast on June 07, 2010, 02:57:48 am
http://www.chemguide.co.uk/mechanisms/nucsub/whatis.html#top (http://www.chemguide.co.uk/mechanisms/nucsub/whatis.html#top)
Post by: Darth Austrakast on June 07, 2010, 03:06:48 am
the melting temperature is highest for silicon as it exist as giant covalent structure -- You have to break a large amount of strong covalent bonds before it will melt or boil.
Phosphorus, sulphur, chlorine and argon are simple molecular substances with only van der Waals attractions between the molecules. Their melting or boiling points will be lower than those of the first four members of the period which have giant structures.
Post by: Ibiza279 on June 07, 2010, 06:43:55 am
Post by: Meticulous on June 07, 2010, 06:47:50 am
hey,the chem guide says that tertiary are the slowest, the fastest are the primary ones :o
Wrong..
Tertiary fastest
Post by: abuelzouz on June 07, 2010, 07:01:04 am
Post by: Darth Austrakast on June 07, 2010, 10:27:35 am
they do say tertiary is fastest ! 8)
By the way How was the chem xam??
24 hours have not passed and we r nt allowed to discuss the xams
I'll just say mine was okay--made some silly errors but overall its was okay and easier than expected
Hopes bio unit 2 will be just as easy
Post by: Kim on June 07, 2010, 10:37:50 am
sum confusin q but overall good
yeh hope bio is good as well
Post by: Meticulous on June 07, 2010, 11:28:09 am
it was good
sum confusin q but overall good
yeh hope bio is good as well
It was perfect alhamdulilah!
Everybody-NO DISCUSSIONS UNTIL 24 HOURS HAVE PASSED!
Post by: Igcseboy on June 07, 2010, 11:35:19 am
It was perfect alhamdulilah!
Everybody-NO DISCUSSIONS UNTIL 24 HOURS HAVE PASSED!
Alhamdulillah it went good ......
Post by: Kim on June 07, 2010, 11:41:22 am
It was perfect alhamdulilah!
Everybody-NO DISCUSSIONS UNTIL 24 HOURS HAVE PASSED!
haha good for u
mine wasnt perfect lol
ok
Post by: Uchia on June 07, 2010, 12:06:06 pm
Post by: Uchia on June 07, 2010, 12:10:20 pm
Post by: Kim on June 07, 2010, 12:22:39 pm
inshallah bio 2 tommorow will also be easy =)
inshallah it will
Post by: Igcseboy on June 07, 2010, 12:44:23 pm
inshallah it will
best of luck to all bio students
By the way i dont take it :P
how was ur other bio papers???
Post by: Darth Austrakast on June 07, 2010, 01:55:41 pm
hey thanx for the wish!
Post by: abuelzouz on June 07, 2010, 04:46:25 pm
hope bio iz gd 2! i did gd in unit 3 :)
Post by: Kraizeee on June 07, 2010, 05:12:19 pm
it was good
sum confusin q but overall good
yeh hope bio is good as well
dont worry
inshallah we'll all get good gradez =)
Post by: Saladin on June 07, 2010, 05:21:02 pm
dont worry
inshallah we'll all get good gradez =)
iA. Everything will work out in the end!
Post by: Uchia on June 07, 2010, 05:39:57 pm
Post by: Darth Austrakast on June 07, 2010, 05:49:09 pm
also chek out biodiversity
and hey this thread is for chem
we should go to the biology section ;) :P :P
Post by: Kim on June 07, 2010, 05:50:12 pm
yeah the cancer thing already came in unit 1
also chek out biodiversity
and hey this thread is for chem
we should go to the biology section ;) :P :P
haha yes we shud
lol
Post by: Uchia on June 07, 2010, 06:09:24 pm
Post by: ksitna on June 07, 2010, 08:54:55 pm
hey guys watch out of the cancer part thingii i have feeling that it might come
what cancer part??????
Post by: Kim on June 07, 2010, 08:56:29 pm
what cancer part??????
ooh that is for bio
Post by: ksitna on June 07, 2010, 08:59:00 pm
ooh that is for bio
well yeah i know but i didnt learn any cancer parts!
Post by: wakemeup on June 08, 2010, 11:22:11 am
Post by: Igcseboy on June 08, 2010, 01:21:40 pm
Wow, othen than the mcqs the paper was surprisingly quite easy. I have high hopes for chemistry now. Hope physics 2 and maths 2 go well too, and then this will be a great ending to an overall frustrating exam session.ya
hopefully its a gr8 end
Post by: sweetsh on June 08, 2010, 04:25:20 pm
Good luck everyone!
Post by: Meticulous on June 08, 2010, 04:26:06 pm
Chemistry Unit 2 was good, not easy, but good. Hope tomorrow's physics& C2 go well.
Good luck everyone!
You're back!
Post by: Darth Austrakast on June 08, 2010, 06:01:33 pm
can anyone discuss the answers??
i forgot everything due to bio 2 :P
Post by: xim7007 on August 15, 2010, 12:17:20 pm
I m stuck on this question. Can anyone post answer for this question before coming tuesday ( 17th august)
Post by: @d!_†oX!© on August 16, 2010, 01:51:10 pm
By the way that would be from CIE, but i don't think that should make much difference...soo...anyone? ::)
Post by: nid404 on August 16, 2010, 01:52:29 pm
Post by: nid404 on August 16, 2010, 01:59:27 pm
When the frequency of the external periodic of force and the body's natural frequency are equivalent, the body vibrates at it's maximum amplitude and this is known as Resonance.
Post by: @d!_†oX!© on August 16, 2010, 02:09:39 pm
I don't mean THAT resonance...i am asking about the resonance in chemistry
Let me give you the definition so you know what i am talking about
Resonance is due to delocalization of 'pi' electrons in a conjugated system
Post by: nid404 on August 16, 2010, 02:32:25 pm
This is a little difficult to explain so I got this from the net...hope you get it
It is a type of electron delocalization. Since electrons repel, if the electrons spread out, it can lead to greater stability.
In order for resonance to occur, you need to have a double bond (mobile high electron density) and a nearby orbital where the double bond can spread out to.
For example, in the following ion
H3C-CH=CH-CH2+
the double bond will be attracted to the positive charge and ends up spread out across two adjacent bonds.
H3C-CH=CH-CH2+ <---> H3C-CH-CH=CH2 (+ charge on carbon2)
Since the electrons are spreading out between the two states ("resonance structures") above, neither of those structures are really a good way to represent the molecule. The closest model of the molecule is a hybrid of the two, with the electrons smeared out over both spots where the double bond can exist. So, they are really each like a bond-and-a-half.
I got this from yahoo answers. I hope you understood.
If you don't understand, I can use benzene as an example which will be more convenient for me to explain.
Post by: @d!_†oX!© on August 16, 2010, 02:47:57 pm
my question is, the example you used...isnt that "position isomerism", cuz all you are doing is transferring the double bond from on position to another...is it the mere fact that it is +vely charged that we call it resonance??
Oh my god...now i feel embarrassed..i know its not such a hard concept but i just cant get it...sorry for troubling you so much.. :-\
Post by: nid404 on August 16, 2010, 03:00:22 pm
I'll use benzene as an example. It has alternating single and double bonds. The structure oscillates between the two forms since the bonding electrons are delocalised.
(http://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2009/06/benzene.jpg)
This is a resonance hybrid when the structure keeps switching.
Post by: The Golden Girl =D on September 20, 2010, 03:11:25 pm
Anyways if u open the Exam Zone Unit 1 Test 1 Question 4)b) as well as C) and d) Please
and with Detailed Explanation Plz :)
Oh and i almost searched almost everywhere to find Amazing notes that give me ALL i need for Unit 1 chem lesson 2 , the section that talks abt enthalpy changes and the whole calculation thing in particular cuz i can't seem to make it FULLLY GLUE into my mind :'(
Thanks *i'm off cuz i have Eng Essay to do -___- so will see this later iA *
FYI Edexcel Chem AS Book ;)
Post by: elemis on September 20, 2010, 03:30:31 pm
Post by: The Golden Girl =D on September 20, 2010, 03:42:33 pm
Try and post a screenshot, more people can help you then.
I'm too embarrassed to say this but whatever ; i have No idea how to make a screen shot :-\ :-X
Well the Only i can do is that the thing is kinda similar to this actually it's the same i guess :
http://answers.yahoo.com/question/index?qid=20071123231452AAg8Kis
and the c part says 0.0500 mol of acid was neautralized in this reaction , calculate delta HEAT of neutralization in kJ/mol.
and part d says suggest y sodium hydroxide is used in SLIGHT excess ?
thx
Post by: elemis on September 20, 2010, 03:53:34 pm
Press it.
Open MS Paint.
Press ctrl + V
Save the file in JPEG format.
Attach the picture here.
Post by: The Golden Girl =D on September 20, 2010, 07:14:11 pm
Near the top right hand corner of your keyboard there should be a button that says scrn shot.
Press it.
Open MS Paint.
Press ctrl + V
Save the file in JPEG format.
Attach the picture here.
Thanks but the thing is I do NOT have a scanner after All O.O
So i really need help if not with the Question then in Fully GLUING the lesson in my mind (Enthalpy Changes and the calculation part of it *in AS Chem*)
Plz , anyone ?
Post by: nid404 on September 20, 2010, 07:20:36 pm
Post by: The Golden Girl =D on September 20, 2010, 07:38:15 pm
Is this the question? http://answers.yahoo.com/question/index?qid=20071123231452AAg8Kis
ya but some values i guess r diff :
50.0 cm-3of 1.00 mol dm-3 of HCl with 50 cm-3 of 1 mol dm-3 NaOH and temperature is 6.90
oh ya and b says Assuming the density is 1.00 g cm-3 and it's heat capacity is 4.18 K-1 g-1 , calculate the heat evolved during the reaction
it's exothermic By the way .
Thx Nid <3
Post by: elemis on September 21, 2010, 01:43:33 pm
Post by: The Golden Girl =D on September 21, 2010, 02:29:57 pm
Post by: The Golden Girl =D on September 25, 2010, 07:35:14 am
when C (s) + 2 H 2 (g) --> CH4 (g)
it's atoms r C (g) + 4 H
what i don't get is :
1. how the hell do i know that delta H of hydrogen is Atomization ?
cuz when we solve it this is how we solve it :
4 delta H - delta H atomization of Carbon + 4 delta H atomization of Hydrogen
I know it's a stupid Question but it's been taking me toooooooooo long to think :'( y is it atomization for the HYDROGEN , it was gas and then gas so no atomization ? idk :-\ :-\
PLZ someone help
Post by: Deadly_king on September 25, 2010, 07:51:02 am
Hmm Okay i got this doubt
when C (s) + 2 H 2 (g) --> CH4 (g)
it's atoms r C (g) + 4 H
what i don't get is :
1. how the hell do i know that delta H of hydrogen is Atomization ?
cuz when we solve it this is how we solve it :
4 delta H - delta H atomization of Carbon + 4 delta H atomization of Hydrogen
I know it's a stupid Question but it's been taking me toooooooooo long to think :'( y is it atomization for the HYDROGEN , it was gas and then gas so no atomization ? idk :-\ :-\
PLZ someone help
The definition for standard enthalpy change of atomisation :
It is the heat energy change when 1 mole of separate gaseous atom of the element is formed from the element under standard state conditions.
Hydrogen exists as H2 molecules under standard state conditions. So you must not omit the delta H atomization of hydrogen since the H2 molecule need to be converted to H atoms.
Do you get me??
If not.......let me know and i'll try to get clearer :)
Post by: The Golden Girl =D on September 25, 2010, 07:54:08 am
The definition for standard enthalpy change of atomisation :
It is the heat energy change when 1 mole of separate gaseous atom of the element is formed from the element under standard state conditions.
Hydrogen exists as H2 molecules under standard state conditions. So you must not omit the delta H atomization of hydrogen since the H2 molecule need to be converted to H atoms.
Do you get me??
If not.......let me know and i'll try to get clearer :)
Aha ya i get it ... thanks loads Mate ;)
Post by: Deadly_king on September 25, 2010, 07:55:53 am
Aha ya i get it ... thanks loads Mate ;)
You are welcome dear :)
Post by: helai.j on September 30, 2010, 06:23:39 pm
and can any one solve A2 edexcel chemistry ann fullick page 15, 2 Questions please ?
Post by: helai.j on October 01, 2010, 08:38:01 am
please someone answer ?
Post by: Deadly_king on October 01, 2010, 08:42:38 am
in the rate of reaction Questions, if the data given is Pressure of the reactant and time, how do i convert the pressure into concentration to draw a concentration/time graph ?
please someone answer ?
Hmm.......can you please upload or write the whole question??
I don't think I can help you with only this little information :-\
Post by: helai.j on October 01, 2010, 09:56:26 am
Q: in a gas phase, molecule A decomposes to molecule B and C at high temperature. A chemist suspects that this reaction is first order with respect to A. in an experiment to explore the kinetics of the reaction, the data in the table were obtained for the decomposition at 800K.
then there is a table with time and partial pressure values for A .
example
T A/KPA
0 1300
20 1051
and so on, then it says by using a graph find out if this reaction is really first order with respect to A.
for the graph i need concentration/time . but they have given me pressure. so how will i make the graph ? or turn the pressure into conc. ?
Post by: The Golden Girl =D on October 02, 2010, 04:42:46 pm
And if yes then where Am i supposed use it ?
Thx
Plz this is Urgent .
Post by: Deadly_king on October 02, 2010, 05:18:25 pm
Hmm .. i have a Q ...." Concentration = Mass/Volume "is there such a formula that exists ?
And if yes then where Am i supposed use it ?
Thx
Plz this is Urgent .
Indeed it exists.
Concentration can be expressed in two units name g/dm3 and mol/dm3
When you are asked to find concentration in terms of g/dm3 then you use the formula. Same principles are applied.
Concentration in g/dm3 = Mr x Concentration in mol/dm3
This is an equation which you need to know as well and will be helpful to you in your calculations.
Hope it helps :)
Post by: The Golden Girl =D on October 02, 2010, 06:09:00 pm
Indeed it exists.
Concentration can be expressed in two units name g/dm3 and mol/dm3
When you are asked to find concentration in terms of g/dm3 then you use the formula. Same principles are applied.
Concentration in g/dm3 = Mr x Concentration in mol/dm3
This is an equation which you need to know as well and will be helpful to you in your calculations.
Hope it helps :)
Ya the Equation does Help but can u explain to me where exactly Ami going to need Concentraction = mass/volume . ...cuz the teacher gave me a H.W. and i solved it ALL in this equation and i got so many mistakes , idk y :-\
Post by: Deadly_king on October 03, 2010, 05:25:24 am
Ya the Equation does Help but can u explain to me where exactly Ami going to need Concentraction = mass/volume . ...cuz the teacher gave me a H.W. and i solved it ALL in this equation and i got so many mistakes , idk y :-\
Hmm.......the way that equation is used will vary with question.
Normally your are given that a certain mass x is dissolved in 100cm3 of solution.
So first you need to find the mass present in 1dm3 of the solution.
Therefore concentration will be the mass calculated in 1 dm3.
It's almost the same principles you apply when using moles to find concentration.
If you have a question, i'll be be able to explain it better ;)
Post by: The Golden Girl =D on October 03, 2010, 11:52:05 am
Hmm.......the way that equation is used will vary with question.
Normally your are given that a certain mass x is dissolved in 100cm3 of solution.
So first you need to find the mass present in 1dm3 of the solution.
Therefore concentration will be the mass calculated in 1 dm3.
It's almost the same principles you apply when using moles to find concentration.
If you have a question, i'll be be able to explain it better ;)
Well i do NOT have a Q , cuz so far we did NOT use it at ALL .....so idk ....the only thing iwant to know is the new Equations like this and how to use them , Thanks :)
Post by: helai.j on October 03, 2010, 03:12:25 pm
Q: the reaction between nitrogen dioxide and carbon monoxide fits the following overall equation:
NO2 + CO ---> NO + CO2
a) if the rate equation suggested a single step mechanism, what would be the rate equation?
b) the rate equation for this reaction is in fact : rate=k[NO2]2
A possible mechanism is:
2NO2 --> NO3 + NO ( step 1 )
NO3 + CO --> NO2 + CO2 ( step 2 )
which of these steps do you think is the rate determining step? explain your answer.
Post by: nid404 on October 03, 2010, 06:21:29 pm
mA+nB--->pC+qD
R= k [A]m [ B]n
a)R=k[NO2][CO]
b) Rate determining step is the slowest step in a mechanism.The second step uses the NO3 produced in the first step. So it is dependent on step 1 for it's NO3. hence Step 1 is the rate determining step.
Post by: nid404 on October 03, 2010, 06:39:15 pm
there is a Question in A2 chemistry ann fullick book page 19 it says
Q: in a gas phase, molecule A decomposes to molecule B and C at high temperature. A chemist suspects that this reaction is first order with respect to A. in an experiment to explore the kinetics of the reaction, the data in the table were obtained for the decomposition at 800K.
then there is a table with time and partial pressure values for A .
example
T A/KPA
0 1300
20 1051
and so on, then it says by using a graph find out if this reaction is really first order with respect to A.
for the graph i need concentration/time . but they have given me pressure. so how will i make the graph ? or turn the pressure into conc. ?
Have the given the equation for the reaction?
Post by: helai.j on October 03, 2010, 08:01:38 pm
thanks again :) <3
Post by: Deadly_king on October 04, 2010, 05:09:33 am
Well i do NOT have a Q , cuz so far we did NOT use it at ALL .....so idk ....the only thing iwant to know is the new Equations like this and how to use them , Thanks :)
Well the equation you wrote is very rarely used.
Most of the time the one I gave you is used. SO no need to worry about the other one ;)
Post by: nid404 on October 04, 2010, 07:35:24 am
thanks for answering the Question and about that previous one i asked, i re-posted it in another post in the science section because no one was replying here and someone answered it for me.
thanks again :) <3
You're welcome :)
Post by: The Golden Girl =D on October 04, 2010, 12:17:03 pm
Well the equation you wrote is very rarely used.
Most of the time the one I gave you is used. SO no need to worry about the other one ;)
OMG .. Srsly that is a Relief for me !!
Jazaka Allah Kulla Kair bro ;)
Post by: Deadly_king on October 04, 2010, 12:32:40 pm
OMG .. Srsly that is a Relief for me !!You are welcome sis :)
Jazaka Allah Kulla Kair bro ;)
We all form part of the huge SF family......so it's quite normal to help each other ;)
Post by: The Golden Girl =D on October 04, 2010, 12:36:44 pm
You are welcome sis :)
We all form part of the huge SF family......so it's quite normal to help each other ;)
so true :D
Post by: The Golden Girl =D on October 06, 2010, 01:44:35 pm
it is asked to find enthalpy change of formation for example : of butane the enthalpy changes given to us are of Combustion graphite , hydrogen and butane but when the teacher solved the Questiong he solved it as if it was a combustion reaction
Now i 'm really confused how can we do that !?
PLZ do Help me :-\ ??? :'(
Post by: Deadly_king on October 06, 2010, 02:10:04 pm
Hey guys i really need this thing it's really Urgent
it is asked to find enthalpy change of formation for example : of butane the enthalpy changes given to us are of Combustion graphite , hydrogen and butane but when the teacher solved the Questiong he solved it as if it was a combustion reaction
Now i 'm really confused how can we do that !?
PLZ do Help me :-\ ??? :'(
Hmm.....it's not that difficult. Let me get it clear for you.
First you need to write equation indicating the formation of butane.
4C + 5H2 ----> C4H10
Since the enthalpy changes of combustion has been given to you, you also need to write the equation relating each substance and its respective combustion.
1. C + O2 ----> CO2 (Enthalpy change of combustion of carbon or graphite)
2. H2 + 0.5O2 ----> H2O (Enthalpy change of combustion of hydrogen)
3. C4H10 + 13/2 O2 ----> 4CO2 + 5H2O (Enthalpy change of combustion of butane)
As you may observe, the combustion of both hydrogen and carbon leads to carbon dioxide and hydrogen as well as the combustion of butane.
Hence, according to Hess's law, we may opt for another route in the conversion of carbon and hydrogen to butane.
Let's say we'll convert 4 moles of carbon and 5 moles of Hydrogen gas to carbon dioxide and water. Then these two products are converted to butane.
In practise these reactions are not feasible. But in theory we may opt for that method to find standard enthalpy changes of a particular reaction.
Let ^C be the enthalpy change of combustion of carbon.
So Enthalpy change of formation of butane = 4(^C) + 5(^H) - (^C4H10)
NOTE : We need to subtract the enthalpy change of combustion since we are converting carbon dioxide and water back to butane whereas the enthalpy change of combustion of butane actually is the energy evolved when 1 mole of butane is completely burnt to carbon dioxide and water. In other words we are doing just the contrary. that's why we need to subtract it.
If you don't understand, let me know :)
Post by: nid404 on October 06, 2010, 02:11:12 pm
Post by: The Golden Girl =D on October 06, 2010, 02:23:01 pm
Hmm.....it's not that difficult. Let me get it clear for you.
First you need to write equation indicating the formation of butane.
C + H2 ----> C4H10
Since the enthalpy changes of combustion has been given to you, you also need to write the equation relating each substance and its respective combustion.
1. C + O2 ----> CO2 (Enthalpy change of combustion of carbon or graphite)
2. H2 + 0.5O2 ----> H2O (Enthalpy change of combustion of hydrogen)
3. C4H10 + 13/2 O2 ----> 4CO2 + 5H2O (Enthalpy change of combustion of butane)
As you may observe, the combustion of both hydrogen and carbon leads to carbon dioxide and hydrogen as well as the combustion of butane.
Hence, according to Hess's law, we may opt for another route in the conversion of carbon and hydrogen to butane.
Let's say we'll convert 4 moles of carbon and 5 moles of Hydrogen gas to carbon dioxide and water. Then these two products are converted to butane.
In practise these reactions are not feasible. But in theory we may opt for that methos to find standard enthalpy changes of a particular reaction.
Let ^C be the enthalpy change of combustion of carbon.
So Enthalpy change of formation of butane = 4(^C) + 5(^H) - (^C4H10)
NOTE : We need to subtract the enthalpy change of combustion since we are converting carbon dioxide and water back to butane whereas the enthalpy change of combustion of butane actually is the energy evolved when 1 mole of butane is completely burnt to carbon dioxide and water. In other words we are doing just the contrary. that's why we need to subtract it.
If you don't understand, let me know :)
I do Understand it but the true Question that is going on and on in my Mind is that is some Questions we are given the Enthalpy changes of Combustion and are asked to find the enthalpy of change of formation of the product
So is that the only way i can get formation is by finding it in combustion (cuz that's the only route we got obvsly)
Ex of my Qs is when they ask for enthalpy of formation of Methane wen they have given us enthalpy change of combustion of it's compouds , another example would be enthalpy of change of fromation of Ammonia ...etc ? :-\ :-\
Post by: The Golden Girl =D on October 06, 2010, 02:31:31 pm
I do Understand it but the true Question that is going on and on in my Mind is that is some Questions we are given the Enthalpy changes of Combustion and are asked to find the enthalpy of change of formation of the product
So is that the only way i can get formation is by finding it in combustion (cuz that's the only route we got obvsly)
Ex of my Qs is when they ask for enthalpy of formation of Methane wen they have given us enthalpy change of combustion of it's compouds , another example would be enthalpy of change of fromation of Ammonia ...etc ? :-\ :-\
Is it really Urgent so Plz do help I have to go cuz of tuition , will be back perhaps late at night if i could iA .
Post by: Deadly_king on October 06, 2010, 04:29:41 pm
I do Understand it but the true Question that is going on and on in my Mind is that is some Questions we are given the Enthalpy changes of Combustion and are asked to find the enthalpy of change of formation of the product
So is that the only way i can get formation is by finding it in combustion (cuz that's the only route we got obvsly)
Ex of my Qs is when they ask for enthalpy of formation of Methane wen they have given us enthalpy change of combustion of it's compouds , another example would be enthalpy of change of fromation of Ammonia ...etc ? :-\ :-\
Hmm..........yeah, this is the only way to find enthalpy changes of formation when you are given enthalpy changes of combustion.
1. Methane is a hydrocarbon, so same principle used for butane is applied here.
2. For ammonia, you should first write its equation of formation, which is :
N2 + 3H2 ----> 2NH3
Therefore the question needs to provide you with the enthalpy changes of combustion of ammonia, nitrogen and hydrogen as well.
Next, you write the equations indicating the combustion of all the reactants and products separately.
1. N2 + 2O2 ---> 2NO2
2. 2H2 + O2 ---> 2H2O
3. 2NH3 + 7/2 O2 ----> 2NO2 + 3H2O
You'll note that the combustion of nitrogen and hydrogen together will form the products of the combustion of ammonia.
So we'll take another route to convert nitrogen and hydrogen to ammonia. First we burn both reactants to obtain nitrogen dioxide and water. Then we convert the latter to ammonia.
Let ^H be the enthalpy change of combustion of hydrogen
So enthalpy change of formation of ammonia will be : ^N + 3(^H) - 2(^NH3)
NOTE : Only one mole of nitrogen and 3 moles of hydrogen are required to form 2 moles of ammonia according to the equation. The number of moles are used as coefficients of enthalpy changes as well as indicated by the bold numbers.
I have applied the same theory as before :)
Post by: The Golden Girl =D on October 06, 2010, 07:15:03 pm
Hmm..........yeah, this is the only way to find enthalpy changes of formation when you are given enthalpy changes of combustion.
1. Methane is a hydrocarbon, so same principle used for butane is applied here.
2. For ammonia, you should first write its equation of formation, which is :
N2 + 3H2 ----> 2NH3
Therefore the question needs to provide you with the enthalpy changes of combustion of ammonia, nitrogen and hydrogen as well.
Next, you write the equations indicating the combustion of all the reactants and products separately.
1. N2 + 2O2 ---> 2NO2
2. 2H2 + O2 ---> 2H2O
3. 2NH3 + 7/2 O2 ----> 2NO2 + 3H2O
You'll note that the combustion of nitrogen and hydrogen together will form the products of the combustion of ammonia.
So we'll take another route to convert nitrogen and hydrogen to ammonia. First we burn both reactants to obtain nitrogen dioxide and water. Then we convert the latter to ammonia.
Let ^H be the enthalpy change of combustion of hydrogen
So enthalpy change of formation of ammonia will be : ^N + 3(^H) - 2(^NH3)
NOTE : Only one mole of nitrogen and 3 moles of hydrogen are required to form 2 moles of ammonia according to the equation. The number of moles are used as coefficients of enthalpy changes as well as indicated by the bold numbers.
I have applied the same theory as before :)
Jazaka allahu kulla kari dude for helping me out :D
Post by: Deadly_king on October 07, 2010, 06:13:39 am
Jazaka allahu kulla kari dude for helping me out :DAnytime :)
I just hope you understood the basic principles so that you can do such questions on your own in the future ;)
Post by: The Golden Girl =D on October 07, 2010, 01:17:01 pm
Anytime :)
I just hope you understood the basic principles so that you can do such questions on your own in the future ;)
I did , don't worry ;)
Post by: Deadly_king on October 07, 2010, 05:29:25 pm
I did , don't worry ;)Now, I can rest in peace ;)
Post by: **RoRo** on October 09, 2010, 02:12:43 pm
A mixture of 10cm3 methane and 10cm3 ethane has sparked with an excess of oxygen. After cooling to room temperature, the residual gas was passed through aqueous potassium hydroxide. Calculate the volume of gas absorbed by the alkali.
Any help in solving it please?
Post by: ashish on October 09, 2010, 02:39:58 pm
10cm^3 10cm^3
C2H6 + 2.5 O2 -----> 2CO2 + 3H2O
10cm^3 20cm^3
in total 30 cm^3 CO2 was released which reacted with alkali
Post by: Deadly_king on October 10, 2010, 08:03:56 am
ok CH4 + 2O2----> CO2 + 2H2OYeah......Ashish is right :)
10cm^3 10cm^3
C2H6 + 2.5 O2 -----> 2CO2 + 3H2O
10cm^3 20cm^3
in total 30 cm^3 CO2 was released which reacted with alkali
From the 1st equation we note that :
1 mole of CH4 burns completely on oxygen to form 1 mole of CO2
I mole is equal to 24dm3 = 24000cm3
Therefore 24000cm3 of methane produces 24000cm3 CO2
Hence 10 cm3 of methane will produce 10cm3 of CO2
Same principle is applied for ethane ;)
Total volume absorbed : 30cm3
Post by: The Golden Girl =D on October 16, 2010, 06:29:16 am
j represent data , in a graphical form , for elements 1 to 36 and use this to explain the meaning of the term " periodic property "
this is in the Chapter "atomic structure and the periodic table" --> mass spectrometer
Thank you in advance :D
Post by: Deadly_king on October 16, 2010, 06:49:53 am
here is a part in the syllabus that i tried to understand but I can't seem to understand it :S
j represent data , in a graphical form , for elements 1 to 36 and use this to explain the meaning of the term " periodic property "
this is in the Chapter "atomic structure and the periodic table" --> mass spectrometer
Thank you in advance :D
I am not sure but I think it's talking about the different trends across a period in the periodic table.
Example : You should know the graph describing the trend of melting points across period 3. There are many graphs each describing a physical property across the period, namely atomic radius, ionic radius, electrical conductivity and first ionisation energy.
You should be able to explain the graph, that is the trend it takes from sodium to chlorine in period 3. The trends will be almost the same across each period and for the same reasons.
I can't seem to link it with mass spectrometry though :-\
Post by: The Golden Girl =D on October 16, 2010, 07:34:31 pm
I am not sure but I think it's talking about the different trends across a period in the periodic table.
Example : You should know the graph describing the trend of melting points across period 3. There are many graphs each describing a physical property across the period, namely atomic radius, ionic radius, electrical conductivity and first ionisation energy.
You should be able to explain the graph, that is the trend it takes from sodium to chlorine in period 3. The trends will be almost the same across each period and for the same reasons.
I can't seem to link it with mass spectrometry though :-\
Aha Okay can u give me an example so that I know what I Exactly Need to know :S
Jazaka Allahu Kulla kair :)
Post by: Deadly_king on October 17, 2010, 07:56:31 am
Aha Okay can u give me an example so that I know what I Exactly Need to know :S
Jazaka Allahu Kulla kair :)
Ok.......i'll elaborate a bit on melting points. You may be asked to plot a graph of melting points against the different elements across the period 3. Find attached a graph, though we are not concerned about boiling points ;) Moreover you need not provide so much detail. A sketch will be more than enough :)
1. Sodium, Magnesium and Aluminium are metals with strong metallic bonds. The melting point increases from Sodium to Aluminium because of stronger metallic bonds due to increase in number of electrons. Hence melting point increases accordingly.
2. Silicon has the highest melting point because a large amount of energy is required to break the strong covalent bonds holding the silicon atoms together in its giant molecular structure.
3. The other elements exist as simple molecules with weak van der Waal's forces holding the molecules together. These forces can be easily broken down leading to a low boiling point.
Among these molecules Sulfur has a slightly higher melting point because it exists as S8 molecules with greater van der Waal's forces of attraction.
You need to know the trend across the period. Most of the time they'll either ask you to plot the graph or you're given the graph and is asked to describe the trend.
Here's a link which explains the other trends ;)
http://www.chemguide.co.uk/inorganic/period3/elementsphys.html#top
I know it seems to be bulky..............but once you understand the principle it becomes easy :D
Anytime sis :)
Post by: The Golden Girl =D on October 17, 2010, 11:53:35 am
Post by: Deadly_king on October 17, 2010, 05:34:37 pm
Thanks Again ;D
Rafwan ukhtii :D
Post by: The Golden Girl =D on October 19, 2010, 01:59:36 pm
http://www.chemguide.co.uk/inorganic/period3/elementsphys.html#top
Fall at Aluminium:
and partially screened by the 3s electrons as well as the inner electrons
Post by: Deadly_king on October 19, 2010, 04:23:43 pm
I don't get this part :S
http://www.chemguide.co.uk/inorganic/period3/elementsphys.html#top
Fall at Aluminium:
and partially screened by the 3s electrons as well as the inner electrons
As you must be aware Aluminium contains more electrons and the latter fills up orbitals in this order :
s ---> p ----> d
The s-orbitals are closer to the nucleus, hence the force of attraction between the nucleus and the electrons from the s-orbitals is stronger.
The p-orbitals are next, hence hence the force of attraction between the nucleus and the electrons from the p-orbitals is stronger than those from the d-orbitals but weaker than those from the s-orbitals.
Moreover the s-orbital being inner the p-orbital acts as a barrier and this reduces the force of attraction between the nucleus and the electrons from the p-orbitals, This is the shielding effect or partially screened.
That is why Aluminium whose outermost electrons are found in p-orbitals have a lower ionisation energy than sodium and magnesium. ;)
Hope it's clear enough :)
Post by: The Golden Girl =D on October 19, 2010, 04:44:38 pm
Thank u D :)
Post by: Deadly_king on October 19, 2010, 05:28:03 pm
Ya so it's because of the More shielding that's caused by the P-orbital ..Nice 8)
Thank u D :)
For Aluminium, it is the s-orbitals that shields the p-orbital since s-orbitals are smaller and closer to the nucleus. ;)
Anytime :D
Post by: The Golden Girl =D on October 19, 2010, 07:35:06 pm
Post by: The Golden Girl =D on October 22, 2010, 05:19:55 pm
Post by: **RoRo** on October 22, 2010, 05:22:10 pm
ok CH4 + 2O2----> CO2 + 2H2O
10cm^3 10cm^3
C2H6 + 2.5 O2 -----> 2CO2 + 3H2O
10cm^3 20cm^3
in total 30 cm^3 CO2 was released which reacted with alkali
Quote
Quote from: ashish on October 09, 2010, 01:39:58 PM
ok CH4 + 2O2----> CO2 + 2H2O
10cm^3 10cm^3
C2H6 + 2.5 O2 -----> 2CO2 + 3H2O
10cm^3 20cm^3
in total 30 cm^3 CO2 was released which reacted with alkali
Yeah......Ashish is right
From the 1st equation we note that :
1 mole of CH4 burns completely on oxygen to form 1 mole of CO2
I mole is equal to 24dm3 = 24000cm3
Therefore 24000cm3 of methane produces 24000cm3 CO2
Hence 10 cm3 of methane will produce 10cm3 of CO2
Same principle is applied for ethane
Total volume absorbed : 30cm3
THANK YOU GUYS SO MUCH!! :)
Thank you so much & I apologize for the late reply!
Post by: **RoRo** on October 22, 2010, 06:20:54 pm
1. Explain why the melting temperature of sodium is much lower than that of magnesium [3 marks]
2. State the type of structure and the nature of the bonding in each of the following elements: [6 marks]
i) aluminium
ii) silicon
iii) chlorine
3. a) Using sodium chloride, hydrogen chloride and copper, explain what is meant by covalent, ionic and metallic bonding. [9 marks]
b) Compare and explain the conduction of electricity by sodium chloride and copper in terms of structure and bonding. [6 marks]
4. Give 5 advantages of alloys. [5 marks]
THANKS A LOT IN ADVANCE! :)
Post by: Deadly_king on October 22, 2010, 06:24:40 pm
Suggest why copper compounds are hazardous ??? *Aslan they're hazardous :o :S *
Hmm........i don't really know about it either :-[
I don't think you need to know about this according to the syllabus.
Anyway to satisfy your curiosity try this :
http://www.scorecard.org/chemical-profiles/summary.tcl?edf_substance_id=CNK750
Hope it helps :)
Post by: The Golden Girl =D on October 22, 2010, 06:34:15 pm
Hmm........i don't really know about it either :-[
I don't think you need to know about this according to the syllabus.
Anyway to satisfy your curiosity try this :
http://www.scorecard.org/chemical-profiles/summary.tcl?edf_substance_id=CNK750
Hope it helps :)
Yes i don't :'(
satisfy my curiosity ? ..nah it came in the Quiz -__-
Anyways thx :)
Post by: Deadly_king on October 22, 2010, 06:36:26 pm
Hey guys, I got a couple of questions here, I grouped them all together to just post it all in one time! LOL :D
1. Explain why the melting temperature of sodium is much lower than that of magnesium [3 marks]
That has already been partially answered in this same thread. Take a look. :D
Unfortunately.............I need to go for now. But i'll help once am back ;)
Sorry for inconvenience.
Post by: Deadly_king on October 22, 2010, 06:38:12 pm
Yes i don't :'(
satisfy my curiosity ? ..nah it came in the Quiz -__-
Anyways thx :)
Oops.......I did not mean to be mean :-[
Sorry................i was not aware that it had something to do with your quiz :-\
Post by: The Golden Girl =D on October 22, 2010, 06:41:03 pm
D --> I know u meant good ...I'm sorry i was being stupid there .
Talk to you later iA :D
Post by: The Golden Girl =D on October 22, 2010, 06:55:37 pm
Hey guys, I got a couple of questions here, I grouped them all together to just post it all in one time! LOL :D
1. Explain why the melting temperature of sodium is much lower than that of magnesium [3 marks]
Magnesium has got 2 PROTONS , hence more nuclear charge .and since thery are in the same period they have same shielding *numebr of shells * ...SO electrons on the shells are ATTRACTED to the proton MORE than Sodium's electrons are *Na has less number of proton , remember ;) *
2. State the type of structure ??? and the nature of the bonding in each of the following elements: [6 marks]
i) aluminium --> Bonding nature - METALLIC
ii) silicon --> Boning nature - GIANT COVALENT BOND
iii) chlorine --> bonding nature - SIMPLE MOLECULAR *of course covalent ;) *
3. a) Using sodium chloride, hydrogen chloride and copper, explain what is meant by covalent, ionic and metallic bonding. [9 marks]
b) Compare and explain the conduction of electricity by sodium chloride and copper in terms of structure and bonding. [6 marks]
4. Give 5 advantages of alloys. [5 marks]
THANKS A LOT IN ADVANCE! :)
That's what i got , my brain isn't working :S :S
Post by: **RoRo** on October 22, 2010, 07:00:45 pm
That has already been partially answered in this same thread. Take a look. :D
Unfortunately.............I need to go for now. But i'll help once am back ;)
Sorry for inconvenience.
Alright, I'll check that out!
& I'll be waiting for your replies!
No problem, its alright! :)
Post by: **RoRo** on October 22, 2010, 07:11:39 pm
Hey guys, I got a couple of questions here, I grouped them all together to just post it all in one time! LOL
1. Explain why the melting temperature of sodium is much lower than that of magnesium [3 marks]
Magnesium has got 2 PROTONS , hence more nuclear charge .and since thery are in the same period they have same shielding *numebr of shells * ...SO electrons on the shells are ATTRACTED to the proton MORE than Sodium's electrons are *Na has less number of proton , remember *
Magnesium has 24 PROTONS, but probably because when it's an ion it forms a +2 charge, it has a more positive charge compared to sodium which forms a +1 charge and hence, magnesium has a higher nuclear charge, so it'll attract more electrons, and hence more energy will be needed to break this force of attraction and hence, a higher melting temperature!
You just gave me an idea on how to write the answer!! Thank you!! :D
2. State the type of structure and the nature of the bonding in each of the following elements: [6 marks]
i) aluminium --> Bonding nature - METALLIC
ii) silicon --> Boning nature - GIANT COVALENT BOND
iii) chlorine --> bonding nature - SIMPLE MOLECULAR *of course covalent *
I don't know what do they mean by "type of structure". It's a question from the textbook.
3. a) Using sodium chloride, hydrogen chloride and copper, explain what is meant by covalent, ionic and metallic bonding. [9 marks]
b) Compare and explain the conduction of electricity by sodium chloride and copper in terms of structure and bonding. [6 marks]
4. Give 5 advantages of alloys. [5 marks]
THANKS A LOT IN ADVANCE!
Thank you for your help!! :)
Post by: The Golden Girl =D on October 22, 2010, 07:14:18 pm
Post by: Deadly_king on October 23, 2010, 04:50:39 am
I can elp tho it'll take time :S
D --> I know u meant good ...I'm sorry i was being stupid there .
Talk to you later iA :D
No.......you were not being stupid. Actually I need to apologise since my words were quite offensive :-[
Sorry again :-\
Anyway seems you understood the trend of melting point across period 3 well ;)
That was a 5 star explanation :D
No worries...............i'll take on the rest :)
Post by: Deadly_king on October 23, 2010, 05:33:55 am
b) Compare and explain the conduction of electricity by sodium chloride and copper in terms of structure and bonding. [6 marks]
i) Sodium chloride conducts electricity in the aqueous form only since it is made up of a compact ionic lattice which gives rise to crystals. In water, however, it dissolves to form Na+ and Cl- ions.
It is these ions which enable sodium chloride to conduct electricity.
ii) Copper is a metal which is composed of Cu atoms in a sea of electrons. They have a strong compact shape due to the strong metallic bonds which exist between the atoms. This also gives rise to a high melting point.
The sea of electrons is formed since each copper atom have 2 electrons in their outermost shell. They are free and mobile. Hence they are able to move from one end to the other but they remain within the metal itself. These electrons are responsible for the ability of copper or any other metal to conduct electricity.
I guess this should be enough to score 6 marks but if you want to know more, try this :
http://www.newton.dep.anl.gov/askasci/phy00/phy00697.htm
http://en.wikipedia.org/wiki/Copper#Electrical_properties
4. Give 5 advantages of alloys. [5 marks]
An alloy is a metal composed of more than one element.
Since it has not mentioned any alloy in particular, your answer can vary to a very large extent.
Advantages of alloys
1. Alloys do not rust. (Example : stainless steel)
2. They are stronger. (Example : steel)
3. They are harder and more resistant. (Example : Aluminium alloy used for making cans)
4. They can be cheaper. (Example : Materials composed of aluminium or silver only is much more expensive than their alloys)
5. Alloys give the possibility to construct a material according to the need. The best alloy to make a bicylce frame need to be strong, corrosion-resistant and beautiful to watch. One metal alone would not be able to provide all these characteristics. Here an alloy would be ideal.
If you have some time, take a look here.
http://www.tutorvista.com/topic/advantages-of-alloys-over-pure-metals
http://www.engr.sjsu.edu/WofMatE/Metals&Alloys.htm
Post by: The Golden Girl =D on October 23, 2010, 06:01:41 am
No.......you were not being stupid. Actually I need to apologise since my words were quite offensive :-[
Sorry again :-\
Anyway seems you understood the trend of melting point across period 3 well ;)
That was a 5 star explanation :D
No worries...............i'll take on the rest :)
Believe they weren't ;)
no problem bro :)
YESH ;D ....
okay :)
Post by: Deadly_king on October 23, 2010, 06:13:16 am
2. State the type of structure and the nature of the bonding in each of the following elements: [6 marks]
i) aluminium
ii) silicon
iii) chlorine
I think GG already stated the nature of bonding. I would just like to add some more ;)
You must first observe that all three of the (aluminium, silicon and chlorine) are in period 3.
As we move from sodium to argon across period 3, the ionic characteristics of the element decreases while their covalent characteristics increase. This is noted by the metallic bonds in sodium and the covalent bonds in chlorine.
However aluminium, despite being a metal also has the characteristics of covalent compounds. Al2Cl6 is covalent.
Type of structure refers to how they exist in nature.
Aluminium usually exists in its ore bauxite.
Silicon exists as a giant molecular structure while chlorine as a simple molecular structure.
3. a) Using sodium chloride, hydrogen chloride and copper, explain what is meant by covalent, ionic and metallic bonding. [9 marks]
i) Sodium chloride is an ionic compound consisting of ions; Na+ and Cl-. The ios have resulted as one electron from sodium has been transferred to chlorine so that both may acquire stable electronic configuration, i.e their outermost shell gets filled.
ii) Hydrogen chloride is on the contrary a covalent compound since hydrogen does not have the capacity to give electrons. So both the hydrogen and chlorine molecule each share one electron such that they end up with a stable electronic configuration,i.e their outermost shell gets filled.
iii) Copper has a metallic lattice composed of copper ions in a sea of electrons. There exist a strong intermolecular force of attraction between the Cu2+ ions and the free delocalised electrons. Hence this gives rise to the compact shape of copper.
This might help you have any doubt :
http://www.beyondbooks.com/psc92/3.asp
Hope it helped :)
Post by: Deadly_king on October 23, 2010, 06:15:05 am
Believe they weren't ;)
no problem bro :)
YESH ;D ....
okay :)
*Glad and reassured* :D
Post by: **RoRo** on October 23, 2010, 07:50:50 am
I think GG already stated the nature of bonding. I would just like to add some more ;)
You must first observe that all three of the (aluminium, silicon and chlorine) are in period 3.
As we move from sodium to argon across period 3, the ionic characteristics of the element decreases while their covalent characteristics increase. This is noted by the metallic bonds in sodium and the covalent bonds in chlorine.
However aluminium, despite being a metal also has the characteristics of covalent compounds. Al2Cl6 is covalent.
Type of structure refers to how they exist in nature.
Aluminium usually exists in its ore bauxite.
Silicon exists as a giant molecular structure while chlorine as a simple molecular structure.
i) Sodium chloride is an ionic compound consisting of ions; Na+ and Cl-. The ios have resulted as one electron from sodium has been transferred to chlorine so that both may acquire stable electronic configuration, i.e their outermost shell gets filled.
ii) Hydrogen chloride is on the contrary a covalent compound since hydrogen does not have the capacity to give electrons. So both the hydrogen and chlorine molecule each share one electron such that they end up with a stable electronic configuration,i.e their outermost shell gets filled.
iii) Copper has a metallic lattice composed of copper ions in a sea of electrons. There exist a strong intermolecular force of attraction between the Cu2+ ions and the free delocalised electrons. Hence this gives rise to the compact shape of copper.
This might help you have any doubt :
http://www.beyondbooks.com/psc92/3.asp
Hope it helped :)
Deadly_king, you're a life-saver!
Thank you so much for your help, I really appreciate it! :)
A question, are you a student? if yes, what subjects are you doing now?
Post by: Deadly_king on October 23, 2010, 07:56:00 am
Deadly_king, you're a life-saver!
Thank you so much for your help, I really appreciate it! :)
A question, are you a student? if yes, what subjects are you doing now?
No problem dude ;)
Anytime :D
Yeah........am doing Chemistry, Physics and Maths for A2 and Bio and GP for AS. Currently in exams :P
What about you ???
It seems you are new here ;)
Post by: **RoRo** on October 23, 2010, 08:26:07 am
I'm doing a full A-level in Math, an AS in Chem and Bio - that's it!! :)
Good luck for your exams!! I'm sure you'll do great!
I was here last year but in the IGCSE thread, now I moved on to AS & A2!! :D
& seriously, you guys are so helpful!
Okay, one more question:
Phosphorus and Sulphur exist as molecules of P4 and S8, respectively. Explain their difference in melting temperatures. [For P it is 317K and for S it is 386K]
I don't know how to word out my answers, I mean I understand why, but I don't know how to write it down or what exactly to write down! :/
Post by: Deadly_king on October 23, 2010, 08:39:23 am
WOW!
I'm doing a full A-level in Math, an AS in Chem and Bio - that's it!! :)
Good luck for your exams!! I'm sure you'll do great!
I was here last year but in the IGCSE thread, now I moved on to AS & A2!! :D
& seriously, you guys are so helpful!
Okay, one more question:
Phosphorus and Sulphur exist as molecules of P4 and S8, respectively. Explain their difference in melting temperatures. [For P it is 317K and for S it is 386K]
I don't know how to word out my answers, I mean I understand why, but I don't know how to write it down or what exactly to write down! :/
I really hope so :)
The slight difference is the result of the size of the molecules. Phosphorus exists as P4 which is smaller than S8. hence it has less Van Der Waal's forces of attraction between the molecules. This is why it has a lower melting point.
This may be useful :
http://www.chemguide.co.uk/inorganic/period3/elementsphys.html#top
Scroll down a bit to reach melting points ;)
Post by: **RoRo** on October 23, 2010, 10:52:55 am
I really hope so :)
The slight difference is the result of the size of the molecules. Phosphorus exists as P4 which is smaller than S8. hence it has less Van Der Waal's forces of attraction between the molecules. This is why it has a lower melting point.
This may be useful :
http://www.chemguide.co.uk/inorganic/period3/elementsphys.html#top
Scroll down a bit to reach melting points ;)
Thanks a lot, the link was really useful, it answered a couple more questions in mind! :)
Post by: Deadly_king on October 23, 2010, 11:57:18 am
Thanks a lot, the link was really useful, it answered a couple more questions in mind! :)
Anytime mate :D
Glad it cleared your doubts ;)
Post by: **RoRo** on October 23, 2010, 03:52:02 pm
1. Why is diamond shiny?
2. Why does PCl3 form a stable compound with BCl3?
3. Urea (NH2)2C=O is commonly used as a fertiliser in most of Europe, whereas ionic ammonium nitrate NH4NO3is the most popular fertiliser in the UK.
Suggest 2 advantages of using urea as a fertilizer compared with ammonium nitrate.
4. Graphite fibres are often used for the brushes [contacts] in electric motors.
i) Give two reasons why graphite fibres are used this way.
ii) Give three reasons why diamonds would be unsuitable for this use.
THANKS A LOT IN ADVANCE!! :)
Post by: Deadly_king on October 23, 2010, 04:25:44 pm
4. Graphite fibres are often used for the brushes [contacts] in electric motors.
i) Give two reasons why graphite fibres are used this way.
ii) Give three reasons why diamonds would be unsuitable for this use.
i) 1. Graphite is a very good conductor of electricity since it has free mobile electrons within its structure.
2. Graphite is made up of carbon which is very common in our daily life. Hence it is readily available.
ii) 1. Diamond is a very bad conductor of electricity since it does not have free delocalised electrons as the carbon atoms are all bonded to four other carbon atoms.
2. Diamond is a very expensive material due to its beauty and use in jewelleries have increased its value.
3. Diamond is one of the hardest substance known on Earth. Moreover it is shiny which makes it a worse radiator of heat.
I'll work out the rest asap ;)
Post by: Uchia on October 23, 2010, 06:21:50 pm
part a only
Post by: Deadly_king on October 24, 2010, 11:13:56 am
1. Why is diamond shiny?
I don't think you need to know that, buddy ;) I had to carry out some research before finding this :
There are 3 properties of a diamond in relation to light :
1. Brilliance : the light reflections caused by the white light that enters the diamond bouncing off its facets inside and exiting the diamond AND also the light that reflects from its surface
2.Fire : the flashes of color, like a rainbow of colors, that you can see in a polished diamond when you move the stone or when you or the light moves. The different colors that make up together the white light that enter the stone are faster or slower than others. When the get reflected inside the gem by its facets and exits the stone, there is a difference in angle between these color rays so you can see separate colors. This creates fire, and it is because of the unique refractive quality diamond has.
3. Scintillation : the flashes of light and the contrasting areas you see when the diamond, the light or the observer moves.
Try not be so curious about things outside the syllabus ;)
2. Why does PCl3 form a stable compound with BCl3?
Such a compound would be theoretically stable because PCl3 has a free lone pair of electrons, while BCl3 is missing a pair of electrons. The lone pair on PCl3 can coordinate to the empty space on BCl3, giving all the atoms an octet.
Hence a coordinate covalent bond is formed between the two molecules to form a rather stable compound which is however quite rare ;)
3. Urea (NH2)2C=O is commonly used as a fertiliser in most of Europe, whereas ionic ammonium nitrate NH4NO3is the most popular fertiliser in the UK.
Suggest 2 advantages of using urea as a fertilizer compared with ammonium nitrate.
1. Urea is readily available through excrements of most organisms. Hence it is cheaper.
2. The yield is extremely high and it has no side-effects on any plants.
If you have time check these :
http://ezinearticles.com/?Beneficial-Uses-of-the-Urea-Fertilizer&id=5229780
http://www.extension.umn.edu/distribution/cropsystems/dc0636.html
Hope it helps :)
Post by: Deadly_king on October 24, 2010, 11:17:15 am
could anyone help me in question 2 page 49 of the edexcel A2 book and thanks
part a only
Hmm............actually I don't have the book right now. :-[
Would you mind to post the question ???
Post by: The Golden Girl =D on October 24, 2010, 02:07:32 pm
No.......you were not being stupid. Actually I need to apologise since my words were quite offensive :-[
Sorry again :-\
Anyway seems you understood the trend of melting point across period 3 well ;)
That was a 5 star explanation :D
No worries...............i'll take on the rest :)
the answer is that HEAVY metals are toxic ;)
Post by: Helium on October 24, 2010, 02:18:33 pm
we had a chem practical test,
making a double salt of ammonium sulfate and iron (II) sulfate,
a question said why is it important to add iron filling to sulfuric acid in small portions rather
than all at once?( i think to avoid a vigorous reaction i have other stuff in mind)
we boiled the sulfuric acid and kept adding small portions, anyone one do this?
oh gg long time not seen,
actually been i while i haven't shown :-[
Post by: The Golden Girl =D on October 24, 2010, 02:22:23 pm
anyone mind, :o
we had a chem practical test,
making a double salt of ammonium sulfate and iron (II) sulfate,
a question said why is it important to add iron filling to sulfuric acid in small portions rather
than all at once?( i think to avoid a vigorous reaction i have other stuff in mind)
we boiled the sulfuric acid and kept adding small portions, anyone one do this?
oh gg long time not seen,
actually been i while i haven't shown :-[
Actually i don't know the asnwer but perhaps to avoid splashes . idk . wait for D to answer u ;)
Well i had the same exact Q but it was copper carbonate and sulhpiric acid --> Answer is : to prevent frothing.
Helium , Aha ....7esabak ma3ai ba3deen :P LOL .... It's Okay but u gotta send me a msg to make up for it tho ;)
Post by: Helium on October 24, 2010, 02:33:58 pm
Actually i don't know the asnwer but perhaps to avoid splashes . idk . wait for D to answer u ;)
Well i had the same exact Q but it was copper carbonate and sulhpiric acid --> Answer is : to prevent frothing.
Helium , Aha ....7esabak ma3ai ba3deen :P LOL .... It's Okay but u gotta send me a msg to make up for it tho ;)
lol
ok thank you :D,
I wonder where the teacher got the practical paper from,
it's called ASD1 Preperation of a double salt
Post by: Deadly_king on October 24, 2010, 02:39:38 pm
the answer is that HEAVY metals are toxic ;)
I think you meant to quote this ;)
could anyone help me in question 2 page 49 of the edexcel A2 book and thanks
part a only
Post by: Deadly_king on October 24, 2010, 02:45:37 pm
anyone mind, :o
we had a chem practical test,
making a double salt of ammonium sulfate and iron (II) sulfate,
a question said why is it important to add iron filling to sulfuric acid in small portions rather
than all at once?( i think to avoid a vigorous reaction i have other stuff in mind)
we boiled the sulfuric acid and kept adding small portions, anyone one do this?
oh gg long time not seen,
actually been i while i haven't shown :-[
Hmm.........i was thinking about it :-\
The only reasonable answer that I can find is that upon addition of the iron fillings, gases are emitted. Hence as a precaution add portion by portion so that gases does not affect experimenter. This is frothing ;)
Moreover, you need to add little by little to make sure that all the iron reacts to form the required salt. You are in some way increasing surface area so that this reaction takes place faster.
Hope I helped :)
Post by: The Golden Girl =D on October 24, 2010, 03:05:45 pm
lol
ok thank you :D,
I wonder where the teacher got the practical paper from,
it's called ASD1 Preperation of a double salt
Anytime :)
Teachers get Qs min ilmiree5 , like seriously LOL xD
Post by: Helium on October 24, 2010, 03:41:44 pm
Hmm.........i was thinking about it :-\
The only reasonable answer that I can find is that upon addition of the iron fillings, gases are emitted. Hence as a precaution add portion by portion so that gases does not affect experimenter. This is frothing ;)
Moreover, you need to add little by little to make sure that all the iron reacts to form the required salt. You are in some way increasing surface area so that this reaction takes place faster.
Hope I helped :)
Yes thank you was helpful,
never knew what was frothing ???, true i never knew hydrogen would choke you so much we had to open the fan,
some started coughing, lol
thanks DK :D
Post by: Helium on October 24, 2010, 03:43:27 pm
Anytime :)
Teachers get Qs min ilmiree5 , like seriously LOL xD
lol thats sometimes so true, u wonder who wrote the question :D
Post by: Helium on October 24, 2010, 04:11:14 pm
Anytime :)
Teachers get Qs min ilmiree5 , like seriously LOL xD
lol i remembered i funny e-mail on how teachers give thier questions,
The teacher looked into the eyes of his students and said:
My sons know that the doctrines of the scholars of the university
Questions abound in the development of seven and best known, there
Doctrine zero
It focuses on the student does not receive more than
Zero in the exam ..
Doctrine scary
Students .. And prove this doctrine that Dr.
Knowledgeable and that he could put tough questions ..
Educational doctrine
A doctrine which remembers all the
Things that forgot to explain tp studenst during the lecture and then
Established in the form of educational questions, students learn
During the exam ...
it's quite long and translated, i'll message it to u.
google translate not that good :-\
Post by: Deadly_king on October 24, 2010, 04:17:35 pm
Yes thank you was helpful,
never knew what was frothing ???, true i never knew hydrogen would choke you so much we had to open the fan,
some started coughing, lol
thanks DK :D
No problem ;)
Glad to have been of help :D
Post by: **RoRo** on October 24, 2010, 05:44:53 pm
I don't think you need to know that, buddy ;) I had to carry out some research before finding this :
There are 3 properties of a diamond in relation to light :
1. Brilliance : the light reflections caused by the white light that enters the diamond bouncing off its facets inside and exiting the diamond AND also the light that reflects from its surface
2.Fire : the flashes of color, like a rainbow of colors, that you can see in a polished diamond when you move the stone or when you or the light moves. The different colors that make up together the white light that enter the stone are faster or slower than others. When the get reflected inside the gem by its facets and exits the stone, there is a difference in angle between these color rays so you can see separate colors. This creates fire, and it is because of the unique refractive quality diamond has.
3. Scintillation : the flashes of light and the contrasting areas you see when the diamond, the light or the observer moves.
Try not be so curious about things outside the syllabus ;)
Such a compound would be theoretically stable because PCl3 has a free lone pair of electrons, while BCl3 is missing a pair of electrons. The lone pair on PCl3 can coordinate to the empty space on BCl3, giving all the atoms an octet.
Hence a coordinate covalent bond is formed between the two molecules to form a rather stable compound which is however quite rare ;)
1. Urea is readily available through excrements of most organisms. Hence it is cheaper.
2. The yield is extremely high and it has no side-effects on any plants.
If you have time check these :
http://ezinearticles.com/?Beneficial-Uses-of-the-Urea-Fertilizer&id=5229780
http://www.extension.umn.edu/distribution/cropsystems/dc0636.html
Hope it helps :)
Thanks a lot!! :)
Post by: mdwael on October 31, 2010, 05:47:52 pm
isnt h-cl polar, and if its polar shouldnt it have dipole-dipole intermolecular forces, which are stronger than induced-dipole forces? why does the mark scheme say other wise? past paper is january 2007 unit 1 q 5 a.
everything has been easy so far, except this..
Post by: Deadly_king on November 01, 2010, 05:33:42 am
okay so this question keeps making mad when I read it, strongest intermolecular force present in liquid h-cl? ans = induced-dipole-induced dipole -_-
isnt h-cl polar, and if its polar shouldnt it have dipole-dipole intermolecular forces, which are stronger than induced-dipole forces? why does the mark scheme say other wise? past paper is january 2007 unit 1 q 5 a.
everything has been easy so far, except this..
HCl is indeed a polar molecule within which there exist permanent dipole-permanent dipole forces of attraction. These forces occurs between the partially negatively charged chlorine and the partially positively charged hydrogen from another molecule. This is because chlorine is electronegative, hence it attracts the shared pair of electrons towards itself.
Now let's get back to your question :
Q : Name the strongest intermolecular force present in liquid HCl
I would have said permanent dipole - permanent dipole forces of attraction.
I can't explain the reasoning of the marking scheme. I guess there might be a mistake or something like that. I'll advise you to consult a tutor. ;)
Post by: Master_Key on November 01, 2010, 09:43:57 am
Post by: Deadly_king on November 01, 2010, 04:52:09 pm
It can be because it not instantaneous-induced diploe, its induced-induced dipole which is more stronger because it stays for a longer time at a particular energy without breaking.
I don't think so.
Permanent dipole is always present in polar molecules whereas induced dipole occurs only when there is a disturbance in the distribution of charges within a molecule.
Post by: Master_Key on November 02, 2010, 12:23:19 pm
Post by: mdwael on November 02, 2010, 01:25:02 pm
HCl is indeed a polar molecule within which there exist permanent dipole-permanent dipole forces of attraction. These forces occurs between the partially negatively charged chlorine and the partially positively charged hydrogen from another molecule. This is because chlorine is electronegative, hence it attracts the shared pair of electrons towards itself.
Now let's get back to your question :
Q : Name the strongest intermolecular force present in liquid HCl
I would have said permanent dipole - permanent dipole forces of attraction.
I can't explain the reasoning of the marking scheme. I guess there might be a mistake or something like that. I'll advise you to consult a tutor. ;)
I totally agree with every word you said, thats what my textbook said and thats what my teacher taught me, Im just mad at the stupid mark scheme which says otherwise. Maybe theres something related to it being in liquid form? because the term liquid was in bold.. anyway thanks for your help.. :)
Post by: Deadly_king on November 02, 2010, 03:13:05 pm
Take an example of water, it is a polar molecule. The degree of polarisation varies, it is not the same always so it seems that these dipole forces must be breaking and forming all the time.
I agree with you here. These induced dipole forces are constantly being formed and broken. However it can't be stronger than the permanent dipoles :-[
I totally agree with every word you said, thats what my textbook said and thats what my teacher taught me, Im just mad at the stupid mark scheme which says otherwise. Maybe theres something related to it being in liquid form? because the term liquid was in bold.. anyway thanks for your help.. :)
Hmm..............HCl exists as H+ and Cl- in the liquid form. Hence this is still permanent dipole forces between the positively charged H+ and the negatively charged Cl-.
Anytime buddy. ;)
Post by: Master_Key on November 03, 2010, 06:14:40 am
I agree with you here. These induced dipole forces are constantly being formed and broken. However it can't be stronger than the permanent dipoles :-[
Permanent dipole-dipole forces are more dominant in solids than in liquids. Take an example of Nylon, it is polar and so it attracts water even when it is not rubbed but water is only attracted to certain degree. This means that the permanent dipole force of nylon is greater. Yes the force of Permanent dipole-dipole is greater than induced dipole forces but the greatest is between sulphide bonds (S-S).
Post by: Deadly_king on November 03, 2010, 03:39:42 pm
Permanent dipole-dipole forces are more dominant in solids than in liquids. Take an example of Nylon, it is polar and so it attracts water even when it is not rubbed but water is only attracted to certain degree. This means that the permanent dipole force of nylon is greater. Yes the force of Permanent dipole-dipole is greater than induced dipole forces but the greatest is between sulphide bonds (S-S).
Yeah I know that buddy. But disulfide bonds occur only in protein. ;)
Nylon cannot be compared to HCl since it is a polymer with much different structures.
Permanent-dipole is much stronger than induced dipole. Am sure about that. :)
Post by: 7d on November 05, 2010, 07:44:16 am
Post 'em all here!!!!
I do Edexcel AS chemistry!
hiii i need help on unit 1 energetics like hess's cycle
i kinda get it but i kinda don't
hehe thanks to anyone who can help
(would be great if you could give me some links) :)
thanks
Post by: Deadly_king on November 05, 2010, 07:59:38 am
hiii i need help on unit 1 energetics like hess's cycle
i kinda get it but i kinda don't
hehe thanks to anyone who can help
(would be great if you could give me some links) :)
thanks
Try this (http://www.chemguide.co.uk/physical/energetics/sums.html) for now. I'll keep adding some new sites. ;)
Post by: 7d on November 05, 2010, 08:03:49 am
Try this (http://www.chemguide.co.uk/physical/energetics/sums.html) for now. I'll keep adding some new sites. ;)
thank you :) this should help xD
Post by: Deadly_king on November 05, 2010, 08:39:52 am
thank you :) this should help xD
Anytime :)
Here (http://www.s-cool.co.uk/alevel/chemistry/chemical-energetics/hess-law.html) is another one. Just in case. ;)
Post by: The Golden Girl =D on November 19, 2010, 03:33:33 pm
http://www.chemguide.co.uk/organicprops/alkenes/dioleqn3.gif
http://www.chemguide.co.uk/organicprops/alkenes/dioleqn4.gif
http://www.chemguide.co.uk/organicprops/alkenes/dioleqn2.gif
If Yes then can you explain it Please :$ :S ?
Thank you in Advance
Post by: Deadly_king on November 19, 2010, 03:54:18 pm
Do I need to know the following equations :
http://www.chemguide.co.uk/organicprops/alkenes/dioleqn3.gif
http://www.chemguide.co.uk/organicprops/alkenes/dioleqn4.gif
http://www.chemguide.co.uk/organicprops/alkenes/dioleqn2.gif
If Yes then can you explain it Please :$ :S ?
Thank you in Advance
Well i don't know about EDEXCEL syllabus but for CIE, you need not know exactly everything about it.
This is about oxidation of alkenes. The latter can be oxidised both under cold and hot conditions but the mechanisms will vary.
You should just know that upon oxidation of alkenes with cold purple KMnO4, a diol will be produced and the purple colour will disappear to give a colourless solution.
If K2Cr2O7 is used as oxidising agent, then the colour change will be from orange to green.
However under hot conditions, colour change will be the same but the C=C will break and each will form compounds with respect to the other group of atoms the carbon is carrying.
If the carbon forming the C=C carries two hydrogen atoms, then carbon dioxide and water will be formed.
If the carbon carrying the C=C carries one hydrogen atom, then it will get oxidised to an aldehyde. If oxidation continues, the aldehyde will get further oxidised to a carboxylic acid.
If the carbon carrying the C=C carries no hydrogen atom, then a ketone will be formed.
Hope it helps :)
If you need any more clarifications, feel free to ask. ;)
Post by: The Golden Girl =D on November 19, 2010, 03:58:17 pm
Post by: Deadly_king on November 19, 2010, 04:03:42 pm
I didn't get the three last parts/ the last two images I posted :$
The last one refers to oxidation under acidic conditions. This will make sure that the resulting mixture will be an acidic compounds.
The one before refers to oxidation under alkaline conditions which will form a salt of the compound.
Example : Ethanol + KMnO4 in NaOH -----> Sodium ethanoate + Mn2+
You need not know how to balance the KMnO4. You can just represent oxidation by [ O ] while reduction is replaced by [H] since it's quite complex to balance it. I don't think it's in the syllabus. ;)
Post by: The Golden Girl =D on November 19, 2010, 04:08:28 pm
The last one refers to oxidation under acidic conditions. This will make sure that the resulting mixture will be an acidic compounds.Okay wait ..... which last two did u refer to the one u talked about or the images I posted :-[ :-\
The one before refers to oxidation under alkaline conditions which will form a salt of the compound.
Example : Ethanol + KMnO4 in NaOH -----> Sodium ethanoate + Mn2+
You need not know how to balance the KMnO4. You can just represent oxidation by
- [/b] while reduction is replaced by [H] since it's quite complex to balance it. I don't think it's in the syllabus. ;)
Post by: Deadly_king on November 19, 2010, 05:03:41 pm
Okay wait ..... which last two did u refer to the one u talked about or the images I posted :-[ :-\
You meant this
http://www.chemguide.co.uk/organicprops/alkenes/dioleqn2.gif
and this
http://www.chemguide.co.uk/organicprops/alkenes/dioleqn4.gif
right??
Post by: The Golden Girl =D on November 20, 2010, 05:39:20 am
Post by: The Golden Girl =D on November 20, 2010, 02:02:10 pm
Can someone help ,Please ?
Post by: Deadly_king on November 21, 2010, 02:23:36 pm
I don't get how to calculate the ppm ? ...it's just ain't getting into my head -.-
Can someone help ,Please ?
Now am not getting you :-[
Can you elaborate a bit? What do you mean by ppm?
Post by: Alpha on November 21, 2010, 02:28:45 pm
Now am not getting you :-[
Can you elaborate a bit? What do you mean by ppm?
She has been banned from posting, on request. But you can communicate via PMs. :)
Post by: Alpha on November 21, 2010, 02:44:52 pm
Post by: guMnam on November 21, 2010, 03:50:17 pm
i need the ans fast.....have to complete ma worksheet :P
Post by: Deadly_king on November 22, 2010, 07:33:11 am
She has been banned from posting, on request. But you can communicate via PMs. :)
Ok, she's been unbanned.
It's alright. I got her pm ;)
Post by: Deadly_king on November 22, 2010, 07:48:03 am
ahem... why does graphite conduct electricity in only one direction while other metals can conduct electricity in all directions ??
i need the ans fast.....have to complete ma worksheet :P
In graphite, each carbon atom uses only 3 of its 4 outer energy level electrons in covalently bonding to three other carbon atoms in a plane. Each carbon atom contributes one electron to a delocalised system of electrons that is also a part of the chemical bonding. The decolcalised electrons are free to move throughout the plane.
For this reason, graphite conducts electricity along the planes of carbon atoms, but does not conduct in a direction at right angles to the plane.
Hope it's clear ;)
Post by: The Golden Girl =D on November 24, 2010, 03:38:08 pm
I really need it :-X :-\
it's Qs :22]b) , 23]d)i) , 24]b)ii)
Thanks In Advance
Post by: The Golden Girl =D on November 24, 2010, 03:44:25 pm
I got a several Question in Chemistry Unit 1 *I'm attaching a Paper (June 2009 Unit 1)
I really need it :-X :-\
it's Qs :22]b) , 23]d)i) , 24]b)ii)
Thanks In Advance
Anyone ? :'(
Post by: Amelia on November 24, 2010, 04:19:42 pm
Anyone ? :'(
Check your inbox.
Post by: The Golden Girl =D on November 24, 2010, 05:12:03 pm
Check your inbox.
Lia Sorry but I got two more :-[ :-X
Q 18]b)ii)...19]c)
Thx :)
Post by: Amii on November 24, 2010, 05:20:06 pm
Anyone ? :'(pm gg :)
Post by: The Golden Girl =D on November 24, 2010, 05:40:42 pm
Lia Sorry but I got two more :-[ :-X
Q 18]b)ii)...19]c)
Thx :)
Anyone ? ???
Post by: Amelia on November 24, 2010, 05:49:18 pm
Lia Sorry but I got two more :-[ :-X
Q 18]b)ii)...19]c)
Thx :)
I can answer Q18bii) - Isomerism in alkenes (Cis & Trans) arises due to double bond between the carbon atom containing one sigma and one pie bond. Presence of pie bonds prevents free rotation of the atoms or groups of atoms attached to the Carbon containing double bonds.
Hex-1-ene the bonds are present between the 1st and 2nd carbon atom, in Hex-2-ene the bonds are present between the 2nd and 3rd Carbon atom.
Post by: The Golden Girl =D on November 24, 2010, 06:05:44 pm
Post by: The Golden Girl =D on November 24, 2010, 06:45:34 pm
Post by: Deadly_king on November 25, 2010, 05:41:19 am
Can anyone do 19 ?!
I believe you were able to do part (a) and (b) yourself.
19.(c) Higher atom economy : Method using ethene.
This is because during this reaction no other products which would lead to loss of atoms are formed. The reaction with ethane however will also form white vapour of HCl which is lost to the surroundings. In other words there is loss of one atom of chlorine and one hydrogen atom.
Higher percentage yield : Method using ethene again.
This is because HCl which is used as reagent in this process is a polar molecule which will immediately cause the reaction to take place. The reaction involving ethane however is free radical reaction and will depend on the probability that the Cl-Cl bond (Cl2 is reagent) is broken.
Moreover if you find the Mr of ethane and ethene, that of ethane is greater by 2 units. So the theoretical yield will be greater for ethene.
Theoretical yield = Mass of product / Mass of reactant x 100
However, here we are asked about the % yield which is give by : actual yield / theoretical yield x 100.
But we have not been given the actual yield. So I can't say this for sure.
NOTE : For the yield, am not sure about it. This is my theory. So I'll recommend to consult your teacher. :)
Post by: The Golden Girl =D on November 27, 2010, 08:10:00 am
Post by: blackberry on November 27, 2010, 08:45:10 am
(hodder education)george facer chem textbook's definiton of a system-term used to represent the reaction mixture,including any solvent and the reaction vessel.
(pearson company)chem student hanbook's definiton of a system-a chemical reaction i.e reactants and products of a reaction are the system
which one is the right definition???!!
Post by: Master_Key on November 27, 2010, 01:10:01 pm
need urgent help guys!!!
(hodder education)george facer chem textbook's definiton of a system-term used to represent the reaction mixture,including any solvent and the reaction vessel.
(pearson company)chem student hanbook's definiton of a system-a chemical reaction i.e reactants and products of a reaction are the system
which one is the right definition???!!
If you will search the third textbook you will get the third definition too.
So it is on your teacher and you to take which one is correct.
Basically both have the same content, but the words differ.
Post by: blackberry on November 27, 2010, 04:11:33 pm
ooo by the way the definitons are almost the same but its the vessel part in which the reaction takes place that both textbuks giv different definitions. one says that the vessel is part of the surroundings and the other says its part of the system. only one can be right but its hard to know which one. i evn checked on the internet and they give different definitions.the teacher just follows the textbook that we use in school so she wudnt know beyond that...... i really need to know what the edexcel people will accept in the exam...... ??? ???
Post by: Deadly_king on November 29, 2010, 12:34:19 pm
For the yield part the first paragraph are u sure of that? If u r could u plz explain it again . Thx :)
Yeah...............am pretty sure about it.
HCl as you now is a polar molecule due to the presence of an electronegative atom; chlorine. Hence it will easily break to give H and Cl atom so that they undergo any particular reaction.
As for the reagent in the 2nd method : Chlorine, it is not polar since both electronegative Cl atoms cancel out each other. Hence for the Cl-Cl bond to break, U.V light is needed. Even when available, there it is probabilistic that this bond breaks. Hence it will take more time.
But now that i think of it, rate of reaction will surely be faster but yield would be the same. So I think this is not the appropriate answer. :-[
Post by: The Golden Girl =D on November 29, 2010, 03:41:49 pm
Yeah...............am pretty sure about it.
HCl as you now is a polar molecule due to the presence of an electronegative atom; chlorine. Hence it will easily break to give H and Cl atom so that they undergo any particular reaction.
As for the reagent in the 2nd method : Chlorine, it is not polar since both electronegative Cl atoms cancel out each other. Hence for the Cl-Cl bond to break, U.V light is needed. Even when available, there it is probabilistic that this bond breaks. Hence it will take more time.
But now that i think of it, rate of reaction will surely be faster but yield would be the same. So I think this is not the appropriate answer. :-[
The Answer that my teacher gave me was as follows :
No other products with different substitutions .
It means that there are NO side products hence the Percentage yield is higher :)
Thanks By the way :)
Post by: Deadly_king on November 29, 2010, 03:46:25 pm
The Answer that my teacher gave me was as follows :
No other products with different substitutions .
It means that there are NO side products hence the Percentage yield is higher :)
Thanks By the way :)
Aah.................I get it now. I used the same explanation for the first part. So I did not heed it for the second.
Anytime GG :)
Post by: The Golden Girl =D on November 29, 2010, 03:47:37 pm
Explain to me how to get to the Answer ,ok ?
June 2010 Unit 1
Qs 4]a) and d) ....5] ..9] I don't get y should we mulitply it by 2/3 ??? ..... 10]
Answers are ; Q4] a) B and d) A ...5] B ......9] C ..... and finally 10] C
Thanks In Advance :)
Post by: elemis on November 29, 2010, 03:51:29 pm
Post by: elemis on November 29, 2010, 03:54:23 pm
Post by: elemis on November 29, 2010, 03:55:53 pm
Since we know that Neon is element C simply count backwards 4 to find that Carbon is actually element A.
Therefore answer is A.
Post by: elemis on November 29, 2010, 04:00:02 pm
Obviously, a cation MUST polarise an anion.
Also, the LARGER the charge on the cation the smaller its radius, the greater the charge density and hence the larger the ability to polarise.
Since we must look for cations with the largest charge we can eliminate C and D.
A and B are left. However they both have the same charge..... what to DO ? :o
Barium is lower in the group than Calcium, correct ? Hence, Barium's radius is larger, correct ? Therefore, its charge density is SMALLER than Calcium.
Hence, answer = B
Post by: The Golden Girl =D on November 29, 2010, 04:01:56 pm
Question 4
why does the one after it HAVE to have a 5 p orbital :-X :-\
the d part I do get it :)
Post by: The Golden Girl =D on November 29, 2010, 04:03:32 pm
Question 5
Obviously, a cation MUST polarise an anion.
Also, the LARGER the charge on the cation the smaller its radius, the greater the charge density and hence the larger the ability to polarise.
Since we must look for cations with the largest charge we can eliminate C and D.
A and B are left. However they both have the same charge..... what to DO ? :o
Barium is lower in the group than Calcium, correct ? Hence, Barium's radius is larger, correct ? Therefore, its charge density is SMALLER than Calcium.
Hence, answer = B
I saw it as Beryllium -.-
Post by: elemis on November 29, 2010, 04:04:04 pm
0.9 * 2/3 = 0.6 moles
Since, moles = volume/24dm3
We get : 0.6 *24
From my workings you can see the answer is C
Post by: elemis on November 29, 2010, 04:06:57 pm
why does the one after it HAVE to have a 5 p orbital :-X :-\
the d part I do get it :)
Wrong. BEFORE IT !!!
The electronic config of Neon is : 1s2 2s2 2p6
Therefore, the element BEFORE it (Fluorine) must be 1s2 2s2 2p5
Therefore it has 5 electrons in its P orbital.
Post by: The Golden Girl =D on November 29, 2010, 04:11:17 pm
But as for Q 9] I don't get why we multiply it by (2/3) ?
you forgot Q10 :-X
Post by: elemis on November 29, 2010, 04:12:25 pm
NaCl ------> Na+ + Cl-
MgCl2 -----> Mg2+ + 2Cl-
Now basically you do : concentration*volume/1000
I'll let you figure it out now, since I've given you the hint :D
Make sure to consider the molar ratios ;)
Post by: elemis on November 29, 2010, 04:14:05 pm
Now I get it :)
But as for Q 9] I don't get why we multiply it by (2/3) ?
you forgot Q10 :-X
Consider it terms of a ratio :
2 moles of SO3 / 3 moles of O2 = X moles of SO3 / 0.9 moles of O2
So you get 2/3 = x/0.9
x = 2/3 * 0.9
Post by: The Golden Girl =D on November 29, 2010, 04:20:03 pm
Thanks mate :)
Post by: elemis on November 29, 2010, 04:44:06 pm
Now I understand them ALL ;D
Thanks mate :)
No worries ;)
Post by: Haaks18 on November 29, 2010, 10:31:50 pm
What does "the bigger charge" means?! does it means the size of the charge :)
Post by: Deadly_king on November 30, 2010, 05:09:48 am
What does thermochemical equation means?!
What does "the bigger charge" means?! does it means the size of the charge :)
In a thermochemical equation, we include the value of DH, the change in enthalpy for the reaction. For example, the equation below showing the combustion of hydrogen would be written as
2H2(g)+ O2(g) ----> 2H2O(g), DH = -571.6 kJ
The sign and magnitude of the change in enthalpy tell us that this reaction is exothermic and gives off a lot of heat. Some rules for writing thermochemical equations are:
1. The sign of DH indicates if the reaction is exothermic (DH negative) or endothermic (DH positive)
2. The coefficients in front of the species represent number of moles
3. The phases of each reactant and product must be indicated: the enthalpy of liquid water at 25oC is different from gaseous water at the same temperature, for example
4. The value of DH is computed with all reactants and products at 25oC and 1 atm pressure unless otherwise indicated.
Here are some examples (http://www.chem.latech.edu/~deddy/chem104/Integrated%20104_Thermo_Eqns.htm) of chemical equations. ;)
Bigger charge only means that the charge on the ion is greater.
Example : Na+ and Mg2+
Mg2+ has the bigger charge since it has a charge of 2 units while Na+ has only one. ;)
Post by: **RoRo** on November 30, 2010, 02:35:36 pm
1. A 5.00g sample of anhydrous Group II metal nitrate loses 3.29g in mass on strong heating. Which metal is present?
A) Magnesium
B) Calcium
C) Strontium
D) Barium
The answer is B) Calcium.
[I found a method to do this, but it's VERYYY time consuming, where I found the no. of moles of each of those 4 metal nitrates and the no. of moles of the metal oxides and calcium was the only one that had the same no. of moles [according to the mole ratio]!
2. The foul smell that skunks spray is due to the number of thiols, one of which is methanethiol CH3SH, which burns as follows:
CH3SH + 3O2 ----> CO2 + SO2 + 2H2O
A sample of 10cm3 of methanethiol was exploded with 60cm3 of oxygen.
What would be the final volume of the resultant mixture of gases when cooled to room temperature?
A) 20cm3
B) 30cm3
C) 50cm3
D) 70cm3
The answer is C) 50cm3
3. The amount of calcium ions in a sample of natural water can be determined by using an ion exchange column.
A 50cm3 sample of water containing dissolved calcium sulphate was passed through the ion exchange resin. Each calcium ion in the sample was exchanged for two hydrogen ions. The resulting acidic solution collected in the flask required 25cm3 of 1.0x10-2mol dm-3 Potassium hydroxide for complete neutralization.
What was the concentration of the calcium sulphate in the original sample?
A) 2.5x10-3 mol dm-3
B) 1.0x10-2 mol dm-3
C) 2.0x10-2 mol dm-3
D) 4.0x10-2 mol dm-3
The answer is A) 2.5x10-3 mol dm-3
& Thanks in advance!! :)
Post by: Amelia on November 30, 2010, 04:43:15 pm
Ans.2) you get the answer by simply subtracting 10 from 60. The 10 cm3 of methanethiol is used up/exploded with 60cm3, so the final volume of the resultant mixture is 50.
Ans 3) - Are you sure the answer is A?, I'm getting it as C.
Each calcium ion in the sample was exchanged for two hydrogen ions.
Therefore, half the concentration of Potassium Hydroxide was required to neutralize the reaction.
(1.0x10-2)X2 = 2.0x10-3
Post by: **RoRo** on December 02, 2010, 06:33:20 am
Ans.1) - Can't think of a better way, myself. Sorry. :-[
Ans.2) you get the answer by simply subtracting 10 from 60. The 10 cm3 of methanethiol is used up/exploded with 60cm3, so the final volume of the resultant mixture is 50.
Ans 3) - Are you sure the answer is A?, I'm getting it as C.
Each calcium ion in the sample was exchanged for two hydrogen ions.
Therefore, half the concentration of Potassium Hydroxide was required to neutralize the reaction.
(1.0x10-2)X2 = 2.0x10-3
It's alright, I've contacted my teacher at school and she's clarified my doubts then!
For 1)
We know that 5g of the Metal nitrate gives 3.29 grams of the mass lost [i.e. nitrogen dioxide and oxygen], so we find the molar mass of the 2 gases which is 216g and then using ratio and proportion we find the molar mass of the metal nitrate which is 328g.
This molar mass is for 2 moles [if you write the equation: 2M(NO3)2 ----> 2MO + 4NO2 + O2 ], so we'll find the molar mass for one mole by dividing 328/2 and we get 164.
So now we know that the Mr of the metal + Mr of the nitrate => 164. We'll get the Mr of the nitrate which is 124, we subtract that from 164, we'll get Mr of the metal which is 40. Calcium which is Answer B has an Mr of 40!
For 2)
CH3SH + 3O2 ----> CO2 + SO2 + 2H2O
1 mole of CH3SH require 3 moles of 3O2 to produce 1 mole of CO2 + 1 mole of SO2 which can be grouped into 2 moles of gases.
They're using 10cm3 of CH3SH so by ration, only 30cm3 of O2 will be required out of the given 60cm3, so the remaining O2 would be 30cm3, in addition to that, since 2 moles of gases will be produced, and they are in the ratio 1:2, so 20cm3 of the gases will be produced, and hence 20+30=50cm3
For 3) It's pretty long, I'll write it down here later!
Post by: The Golden Girl =D on December 02, 2010, 07:27:51 am
1. a solution is prepared by dissloving 0.475g of (NH4)2SO4 (Mr =118)in enough of distilled water and the solution is made up to 2.0 dm3
Calculate the ppm of
a] NH4 + b] SO4 2-
BOLD is the charge
2. a 10% (by mass) of CO is ...
A. 100,000 ppm
B. 10,000 ppm
C. 28,000 ppm
D. 10,000,000 ppm
3. Fuel manufacturers recommend carbon monoxide levels be between 0.5 to 0.7 % at full load .Many measure CO in parts per million , ppm .
What is concentration in ppm of 0.5 % ?
Thanks In Advance :)
Post by: Deadly_king on December 02, 2010, 07:50:08 am
D here are the ppm Questions I told you about .
2. a 10% (by mass) of CO is ...
A. 100,000 ppm
B. 10,000 ppm
C. 28,000 ppm
D. 10,000,000 ppm
Definition of ppm
This is a way of expressing very dilute concentrations of substances. Just as per cent means out of a hundred, so parts per million or ppm means out of a million. Usually describes the concentration of something in water or soil. One ppm is equivalent to 1 milligram of something per liter of water (mg/l) or 1 milligram of something per kilogram soil (mg/kg).
This somehow eases the 2nd question. ;)
In other words 10/100 of CO is also equal to 100000/1000000 CO.
Hence answer is A.
3. Fuel manufacturers recommend carbon monoxide levels be between 0.5 to 0.7 % at full load .Many measure CO in parts per million , ppm .
What is concentration in ppm of 0.5 % ?
Again since the level of CO is 0.5% : 0.5/100, we just need to convert the denominator from 100 to 1000000.
In this way we'll be getting 5000/1000000.
Hence answer is 5,000 ppm. ;)
If you wanna know more about ppm. click here (http://www.engineeringtoolbox.com/ppm-d_1039.html). :D
Post by: elemis on December 02, 2010, 07:52:14 am
0.475/132 = 3.598 *10^-3 moles of Ammonium Sulphate
2*[3.598 *10^-3] = 7.197*10^-3 NH4+ ions
Since concentration = no. of moles / volume
c = 7.197*10^-3 / 2 = 3.598*10^-3 moldm-3
Converting moldm-3 to gdm-3 gives : 0.475 gdm-3
Converting gdm-3 to milligrams per dm3
we get 475 mgdm-3 or 475 ppm
Is this correct ?
It is important to note that 1 ppm = 1 milligram per decimeter cube.
Post by: The Golden Girl =D on December 02, 2010, 09:00:37 am
Definition of ppm
This is a way of expressing very dilute concentrations of substances. Just as per cent means out of a hundred, so parts per million or ppm means out of a million. Usually describes the concentration of something in water or soil. One ppm is equivalent to 1 milligram of something per liter of water (mg/l) or 1 milligram of something per kilogram soil (mg/kg).
This somehow eases the 2nd question. ;)
In other words 10/100 of CO is also equal to 100000/1000000 CO.
Hence answer is A.
Again since the level of CO is 0.5% : 0.5/100, we just need to convert the denominator from 100 to 1000000.
In this way we'll be getting 5000/1000000.
Hence answer is 5,000 ppm. ;)
If you wanna know more about ppm. click here (http://www.engineeringtoolbox.com/ppm-d_1039.html). :D
OMG I didn't know it's that easy :-X :-[
How about the first Q ?
Sorry I know I got Loads of doubts in other stuff I'll post it as soon as I'm done with it iA :)
I don't get the dative bond , especially when there is a Q that says which of the compounds has a dative bond , how do I know that ? :-\
I got a problem with naming organic compounds and sometimes the geometric isomers if it's drawn and I'm supposed to name it , you know :-X (can u give me a website so that I can have more practice on it ? *
Thanks Loads mates :)
Post by: elemis on December 02, 2010, 09:01:56 am
Post by: The Golden Girl =D on December 02, 2010, 09:02:58 am
I've answered the (a) part of the first question. Tell me if my answer is correct.
the thing is the booklet the teacher gave me has NO marking scheme or anything so I don't know :-\
Post by: elemis on December 02, 2010, 09:25:57 am
I don't get the dative bond , especially when there is a Q that says which of the compounds has a dative bond , how do I know that ? :-\
Give me an example question.
Post by: The Golden Girl =D on December 02, 2010, 09:29:44 am
Give me an example question.
Which of the following pairs do NOT form a dative covalent bond to each other ?
A. NH3 and H+
B. H2O and H+
C.NH3 and BF3
D.CH4 and AlCl3
the Answer is D
Post by: elemis on December 02, 2010, 09:42:05 am
Ammonia and a Hydrogen ion form an Ammonium ion NH4+ with a dative bond between Hydrogen ion and Nitrogen.
See pic 1
H2O and H+ form an Oxonium Ion which is again a textbook example of dative bonding.
For C look at pic 2
As we have eliminated A, B and C. D is the only option remaining and hence the answer.
Post by: The Golden Girl =D on December 02, 2010, 09:46:09 am
A and B are eliminated because they are textbook examples of dative bonding.
Ammonia and a Hydrogen ion form an Ammonium ion NH4+ with a dative bond between Hydrogen ion and Nitrogen.
See pic 1
H2O and H+ form an Oxonium Ion which is again a textbook example of dative bonding.
For C look at pic 2
As we have eliminated A, B and C. D is the only option remaining and hence the answer.
Can u draw D as well so that I can see the difference Please ?
Post by: elemis on December 02, 2010, 09:58:27 am
Can u draw D as well so that I can see the difference Please ?
I'm not sure how it will look. I dont even think they bond :S
Post by: Deadly_king on December 02, 2010, 10:08:56 am
Which of the following pairs do NOT form a dative covalent bond to each other ?
A. NH3 and H+
B. H2O and H+
C.NH3 and BF3
D.CH4 and AlCl3
the Answer is D
I just wanted to make it clearer.
A dative bond is formed when one of the atoms or molecules forming the final product has a lone pair of electron which it can donate to the other atom or molecule who on the contrary can accept a pair of electron to attain the stable electronic configuration of a stable gas.
A : H+ lacks an electron which means its electronic configuration is 1s0. Hence it can accept a pair of electron. This pair of electron comes from the ammonia molecule which has one lone pair of electron on the nitrogen atom which is also bonded to 3 other hydrogen atoms.
D : CH4 ----> All the atoms involved in this molecule namely both carbon and hydrogen have stable electronic configuration. Hence they cannot form any further bond. All the orbitals of carbon has been filled from the electrons which it is sharing with the 4 hydrogen atoms.
Post by: Deadly_king on December 02, 2010, 10:11:43 am
I'm not sure how it will look. I dont even think they bond :S
Indeed they will not form any bond.
They will remain as such; two separate molecules.
This is why it is the answer to the question. ;D
Post by: The Golden Girl =D on December 02, 2010, 10:16:02 am
but what abt the naming doubt ?
D can u check the first Q I posted at the ppm ?
thx
Post by: Deadly_king on December 02, 2010, 10:22:31 am
Aha Okay ,now I get it =D
but what abt the naming doubt ?
D can u check the first Q I posted at the ppm ?
thx
Am still looking for a website which might help you. :-[
Yeah..............I already did. According to me Ari did it well. ;)
But if you don't understand, do let me know and i'll try to elaborate as much as possible. :)
Post by: The Golden Girl =D on December 02, 2010, 10:26:30 am
Am still looking for a website which might help you. :-[
Yeah..............I already did. According to me Ari did it well. ;)
But if you don't understand, do let me know and i'll try to elaborate as much as possible. :)
No Probs , me waiting ^_^
well in that case I do Understand it ^_^
Ari -> thanks a lot mate =D
Nah no need to :)
Post by: Deadly_king on December 02, 2010, 11:47:31 am
No Probs , me waiting ^_^
well in that case I do Understand it ^_^
Ari -> thanks a lot mate =D
Nah no need to :)
Alright then. :D
Glad that you understood.
Well this (http://www.chemguide.co.uk/basicorg/convmenu.html#top) is the best that I could find. I'll continue to look for others and will keep you uptodate. ;)
Hope it helps :)
Post by: The Golden Girl =D on December 02, 2010, 11:59:09 am
Post by: The Golden Girl =D on December 03, 2010, 06:40:53 am
http://www.chembio.uoguelph.ca/educmat/chm19104/nomenclature/quizes.html
I have some doubts -.-
Quiz 1 , Q4]
and Quiz 2 Q1]
Post by: Weaam on December 03, 2010, 09:31:04 am
The paper doesnt say any date or anything, it just says Sample Assessment Material under Unit 1 : The core principles of chemistry.
On the bottom it says Edexcel Limited 2007.
If anyone can find it please let me know.
Thankss ;D
Post by: The Golden Girl =D on December 03, 2010, 09:34:52 am
tho check the Q paper first tho :)
Post by: The Golden Girl =D on December 03, 2010, 09:47:40 am
D , found one Alhamdulilah =D
http://www.chembio.uoguelph.ca/educmat/chm19104/nomenclature/quizes.html
I have some doubts -.-
Quiz 1 , Q4]
and Quiz 2 Q1]
Anyone ? :-\
Post by: Deadly_king on December 03, 2010, 10:00:13 am
D , found one Alhamdulilah =D
http://www.chembio.uoguelph.ca/educmat/chm19104/nomenclature/quizes.html
I have some doubts -.-
Quiz 1 , Q4]
and Quiz 2 Q1]
I've been trying it since an hour now but I can't seem to get the correct answer. :-[
According to me Quiz 1, Q4 is 2-methyl,3-ethyl pentane
Quiz 2 Q1 ----> 1-dimethyl,2-ethyl cyclohexane
But the system is saying it's not right. :-\
Post by: Amii on December 03, 2010, 10:03:55 am
Hey guys, so our teacher gave us this past paper for homework and i need to check some things on the markscheme but i cant well, find it.I think this is the file - the question paper and the answers both are there
The paper doesnt say any date or anything, it just says Sample Assessment Material under Unit 1 : The core principles of chemistry.
On the bottom it says Edexcel Limited 2007.
If anyone can find it please let me know.
Thankss ;D
Take care :D
Post by: The Golden Girl =D on December 03, 2010, 10:05:58 am
I've been trying it since an hour now but I can't seem to get the correct answer. :-[
According to me Quiz 1, Q4 is 2-methyl,3-ethyl pentane
Quiz 2 Q1 ----> 1-dimethyl,2-ethyl cyclohexane
But the system is saying it's not right. :-\
I know right -.-
Thanks man , At least u confirmed my answer =D
Post by: The Golden Girl =D on December 03, 2010, 10:07:03 am
I think this is the file - the question paper and the answers both are there
Take care :D
girl there is no MS for it or ? :-[
Post by: Deadly_king on December 03, 2010, 10:11:34 am
I've been trying it since an hour now but I can't seem to get the correct answer. :-[
According to me Quiz 1, Q4 is 2-methyl,3-ethyl pentane
Quiz 2 Q1 ----> 1-dimethyl,2-ethyl cyclohexane
But the system is saying it's not right. :-\
I think I got it now............I had put it in the wrong order. :-[
Quiz 1 Q4 is 3-ethyl-2-methylpentane
Quiz 2 Q1 is 2-ethyl-1,1-dimethylcyclohexane ;)
Post by: The Golden Girl =D on December 03, 2010, 10:12:35 am
Post by: Amii on December 03, 2010, 10:24:15 am
girl there is no MS for it or ? :-[The answers are given ----> look from page 129 :D
Post by: The Golden Girl =D on December 03, 2010, 10:28:02 am
The answers are given ----> look from page 129 :D
Love ya ;D :D :D :D :D
Post by: Amii on December 03, 2010, 10:32:16 am
Love ya ;D :D :D :D :DLove you too ;D
Post by: Weaam on December 03, 2010, 10:59:47 am
I think this is the file - the question paper and the answers both are there
Take care :D
THAAAAAANK YOUUUUUU!! ;DDD
Post by: Amii on December 03, 2010, 11:10:27 am
THAAAAAANK YOUUUUUU!! ;DDDNo problem :D
Post by: Weaam on December 03, 2010, 11:22:03 am
No problem :DDudee, ur a life saverrrr ;)
Post by: The Golden Girl =D on December 04, 2010, 03:49:08 pm
Q5] , Q9]a)c) , Q11]a) b) .... Q12 ] and 13] ..Q15]e)i) ii)
I'll come back tmrrw if I have any further doubts iA
Thanks :)
Post by: Amelia on December 04, 2010, 04:39:10 pm
Hence, the equation would be: 2 C(s) + 3 H2(g) + 0.5 O2(g) --> C2H5OH(l)
So, the answer is D.
9)a) Ionization Energies decreases down the group, the greater the atomic number - size of the atom increases resulting in less nuclear pull.
So, the answer is A.
c) Noble gases have filled shells, which is the most stable configuration for an atom. Removing an electron from a noble gas would increase the energy more than if you removed an electron from, for example, nitrogen.
Answer is D (though I'm not sure about this one. :-[)
Post by: Amii on December 04, 2010, 04:46:36 pm
Post by: Amelia on December 04, 2010, 04:56:23 pm
C2H4+ Br2-> C2H4Br++ Br-
C2H4Br++ Cl--> C2H4BrCl
Ans is B.
Post by: Amii on December 04, 2010, 05:01:00 pm
CH3 Cl
C = C
H CH3
Here the high priority ones are Carbon and Chlorine - both are on the same side so Z
The Cl atom is attached to the 2 carbon(as it should get the smallest no possible) so
Z-2-Chlorobut-2-ene
According to me D should be the answer
but C in the ms I dont understand why - Liaaaaaaaaa help ???
Post by: Amelia on December 04, 2010, 05:18:45 pm
13) D
CH3 Cl
C = C
H CH3
Here the high priority ones are Carbon and Chlorine - both are on the same side so Z
The Cl atom is attached to the 2 carbon(as it should get the smallest no possible) so
Z-2-Chlorobut-2-ene
It is D, something's up with the markscheme.
According to me D should be the answer
but C in the ms I dont understand why - Liaaaaaaaaa help ???
[/quote]
Post by: Amii on December 04, 2010, 05:27:27 pm
1.20 nanomole dm -3 should be converted to mol cm-3so
since 1 mol = 10-9 nanomol
1.20 * 10 -9
then to covert the dm3
1000 cm3= 1 dm3
1.20 * 10 -9 *10-3
=1.20 * 10 -12 mol dm-3
C=n/V
Volume = 1cm3
so C*n=(1.20*10-12 ) *1 = 1.20*10-12 moles
the Mr of Mg = 24.3
n=m/Mr
m=n*Mr
m=(1.20*10-12 ) * 24.3
=2.916*10-11
=2.92*10-11 g
Post by: Amelia on December 04, 2010, 05:34:46 pm
Addition reaction of C4H10
b) Ans is C - presence of Double bonds.
Thanks, Mr. Holmes. ;D
Post by: Amii on December 04, 2010, 05:40:16 pm
11a) it's D.I should be thanking you Prince hamlet :D +rep ---- 1 is already pending
Addition reaction of C4H10
b) Ans is C - presence of Double bonds.
Thanks, Mr. Holmes. ;D
thanxxxx liaaaa-love you ;D
hey check the 15th one - my answering way looks very messy :(
Post by: Amelia on December 04, 2010, 06:13:12 pm
I should be thanking you Prince hamlet :D +rep ---- 1 is already pending
thanxxxx liaaaa-love you ;D
hey check the 15th one - my answering way looks very messy :(
It's fine, as long as GG can understand. :P
Post by: The Golden Girl =D on December 05, 2010, 03:19:49 pm
Post by: **RoRo** on December 05, 2010, 05:40:46 pm
Thanks in advance! :)
Post by: Amelia on December 05, 2010, 06:00:14 pm
or just click on da link for a bigger image.
(http://www.tutornext.com/system/files/u73/Chapter%203-final-10.gif)
http://www.tutornext.com/system/files/u73/Chapter%203-final-10.gif
Post by: The Golden Girl =D on December 05, 2010, 06:42:51 pm
9)a) Ionization Energies decreases down the group, the greater the atomic number - size of the atom increases resulting in less nuclear pull.
So, the answer is A.
c) Noble gases have filled shells, which is the most stable configuration for an atom. Removing an electron from a noble gas would increase the energy more than if you removed an electron from, for example, nitrogen.
Answer is D (though I'm not sure about this one. :-[)
not it's A .
Post by: The Golden Girl =D on December 05, 2010, 06:45:11 pm
11a) it's D.
Addition reaction of C4H10
b) Ans is C - presence of Double bonds.
Thanks, Mr. Holmes. ;D
Hmm 11]a is A By the way , and c) is C
I don't get them AT ALL T_T
Post by: The Golden Girl =D on December 05, 2010, 07:01:26 pm
Post by: Amii on December 05, 2010, 07:07:27 pm
not it's A .gg check again ;)
9c is D
Post by: The Golden Girl =D on December 05, 2010, 07:13:26 pm
gg check again ;)
9c is D
i don't get 9]c) and a) + 11] as well
I need this for tmrrw so plz help :(
Post by: The Golden Girl =D on December 05, 2010, 07:28:52 pm
(NH4)2SO4 -----> 2NH4+ + SO42-
0.475/132 = 3.598 *10^-3 moles of Ammonium Sulphate
2*[3.598 *10^-3] = 7.197*10^-3 NH4+ ions
Since concentration = no. of moles / volume
c = 7.197*10^-3 / 2 = 3.598*10^-3 moldm-3
Converting moldm-3 to gdm-3 gives : 0.475 gdm-3
Converting gdm-3 to milligrams per dm3
we get 475 mgdm-3 or 475 ppm
Is this correct ?
It is important to note that 1 ppm = 1 milligram per decimeter cube.
how did you do this Ari ? :-\ :-[
Post by: **RoRo** on December 05, 2010, 07:46:59 pm
Yes, you do need to know them. d-orbitals are double dum-bell in shape. Look at the image below, you'll understand. ;)
or just click on da link for a bigger image.
(http://www.tutornext.com/system/files/u73/Chapter%203-final-10.gif)
http://www.tutornext.com/system/files/u73/Chapter%203-final-10.gif
Thanks Hamlet! :)
Post by: Amii on December 05, 2010, 07:56:53 pm
More energy is required to remove the 2nd electron than to remove the 1st electron.
This is because the 2nd electron is being removed from a postive ion,which is smaller than the original atom and experiences greater force of attraction.
Even more energy would be required toremove the 3rd electron and so on.
Hence the IE5>IE4>IE3>IE2>IE1 - should increase
so ofcourse not A or C.
Then if you look at B there is a big jump between the 1st IE and 2nd IE ---->which shows the second electron is being removed from the another inner shell.
But nobles gases have 8 electrons in the outer most shell - which means all the 5 electrons will be removed from the same shell - hence there should no jump in the values between the first 5 IE .
Therefore D - IE increases and no jump in the IE values
This is what I think :-\
I am sorry if it's confusing :(
Post by: Amii on December 05, 2010, 08:17:20 pm
Down a group
The no. of shells increases that is more shielding effect.The electrons of the inner shells screen the attraction between the nucleus and the outer shell electrons.Hence it is easier to remove the electron.
Hence IE decreases down the group
Answer----> A
Post by: Amii on December 05, 2010, 09:04:16 pm
anyway
the question says which compound is formed from one of the others in an addiction reaction.
Since it is an addition reaction the compund will be formed from a compund containing a double bond which is B.
The double bond is between the 2nd and 3rd carbon - when the pie bond breaks, the 2 new sigma bonds should be formed on the 2nd and 3rd carbon atom.
Not D---->The bromine atoms are attached to the 1st and 2nd carbon atoms.
Not B----> only 1 new sigma bond formed - and the chain is branched - no proper explanation for why not B but it is obvious right that the ans is not B
answer---->A
H H H H H H
H-C- C = C - C -H + H2 -----> H-C-C-C-C-H
H H H H H H H H
Post by: **RoRo** on December 06, 2010, 06:13:41 am
It's from the topic Atomic Structure [Unit 1]
1. The p orbital will have less energy compared to the s orbital because s is more stable.
2. p6 has more energy compared to p5 and p3 has more energy compared to p2 because p6 and p3 are more stable compared to p2 and p3.
3. As the distance from the nucleus increases, the energy of the shell increases as it is further apart, so there is less attraction of the electrons by the nucleus and hence it is less stable.
& my fourth question is how do you draw the energy level diagram for lets say Magnesium?
Use this symbol [] to represent the 2 opposite arrows.
Thank you!
Post by: elemis on December 06, 2010, 10:53:30 am
how did you do this Ari ? :-\ :-[
You mean how I converted from moldm-3 to gdm-3 ?
All I did was multiply by the molar mass of the compound.
To convert gdm-3 to mgdm-3 I simply multiplied by 1000 because there are 1000 mg in one gram.
Post by: The Golden Girl =D on December 06, 2010, 12:05:10 pm
okay 9 c
More energy is required to remove the 2nd electron than to remove the 1st electron.
This is because the 2nd electron is being removed from a postive ion,which is smaller than the original atom and experiences greater force of attraction.
Even more energy would be required toremove the 3rd electron and so on.
Hence the IE5>IE4>IE3>IE2>IE1 - should increase
so ofcourse not A or C.
Then if you look at B there is a big jump between the 1st IE and 2nd IE ---->which shows the second electron is being removed from the another inner shell.
But nobles gases have 8 electrons in the outer most shell - which means all the 5 electrons will be removed from the same shell - hence there should no jump in the values between the first 5 IE .
Therefore D - IE increases and no jump in the IE values
This is what I think :-\
I am sorry if it's confusing :(
Highest I.E. is for the Noble Gas , hence the Highest I.E. in the list is for Noble gases hence it's C
11]a) it does make sense to me :)
Thanks ;D
You mean how I converted from moldm-3 to gdm-3 ?Ahh k , thanks mate :)
All I did was multiply by the molar mass of the compound.
To convert gdm-3 to mgdm-3 I simply multiplied by 1000 because there are 1000 mg in one gram.
Post by: elemis on December 06, 2010, 12:21:29 pm
Ahh k , thanks mate :)
No worries. If possible, please check those answers with your teacher.
Post by: The Golden Girl =D on December 06, 2010, 12:24:21 pm
No worries. If possible, please check those answers with your teacher.
I'll try iA :)
Post by: Deadly_king on December 06, 2010, 12:32:59 pm
I take down notes while my teacher is speaking and this is what I have, some of it just doesn't make sense to me, can someone please go through them and correct me if I am wrong?
It's from the topic Atomic Structure [Unit 1]
1. The p orbital will have less energy compared to the s orbital because s is more stable.
2. p6 has more energy compared to p5 and p3 has more energy compared to p2 because p6 and p3 are more stable compared to p2 and p3.
3. As the distance from the nucleus increases, the energy of the shell increases as it is further apart, so there is less attraction of the electrons by the nucleus and hence it is less stable.
& my fourth question is how do you draw the energy level diagram for lets say Magnesium?
Use this symbol [] to represent the 2 opposite arrows.
Thank you!
I think this (http://www.chemguide.co.uk/atoms/properties/atomorbs.html) will help you. ;)
If you still have any doubts, feel free to ask. :)
Post by: **RoRo** on December 06, 2010, 04:47:00 pm
I think this (http://www.chemguide.co.uk/atoms/properties/atomorbs.html) will help you. ;)
If you still have any doubts, feel free to ask. :)
Thanks a lot! :)
One more question: why does HBr have a higher boiling point that HCl?
Shouldn't it be the opposite? :/
Post by: Amelia on December 06, 2010, 05:20:33 pm
You are welcome. ;)
Post by: **RoRo** on December 06, 2010, 05:25:58 pm
In case of HBr and HCl, the most dominant intermolecular forces in them are dispersion forces. Dispersion forces greatly depend on the size of the molecule. i.e. bigger the molecule --> more the number of bonds --> higher the energy require to break the bond for vaporization --> consequently, higher the boiling point. If u look at the periodic table, you will find Br in the row lower than Cl meaning Br atom is bigger than Cl ( note: the size of atom or atomic radius increases as you go down the periodic table). That's why HBr has greater boiling point than HCl.
You are welcome. ;)
Can I ask you a question, what do you mean by dispersion forces?
I understood the concept By the way, thank you! :)
Post by: Amelia on December 06, 2010, 05:35:00 pm
Definition of dispersion forces (also called London dispersion forces or Wander-wal's forces or induced dipole-induced dipole forces)
Dispersion is an intermolecular attraction force that exists between all molecules. These forces are the result of the movement of electrons which cause slight polar moments. Dispersion forces are generally very weak but as the molecular weight increases so does their strength.
The Dispersion force is due to the movement of electrons in a molecule or an atom, the electrons are in continuous motion. At any point of time at one part og hte molecule there will be one more electron than the other. This part of the molecule induces slightly negetice charge while the other part induces slightly positive charge. The attraction between non-polar molecules give rise to dispersion forces.
P.S- Hope it helped! Anytime. ;)
Post by: **RoRo** on December 06, 2010, 07:22:48 pm
oh, sorry. I thought you knew what it meant.
Definition of dispersion forces (also called London dispersion forces or Wander-wal's forces or induced dipole-induced dipole forces)
Dispersion is an intermolecular attraction force that exists between all molecules. These forces are the result of the movement of electrons which cause slight polar moments. Dispersion forces are generally very weak but as the molecular weight increases so does their strength.
The Dispersion force is due to the movement of electrons in a molecule or an atom, the electrons are in continuous motion. At any point of time at one part og hte molecule there will be one more electron than the other. This part of the molecule induces slightly negetice charge while the other part induces slightly positive charge. The attraction between non-polar molecules give rise to dispersion forces.
P.S- Hope it helped! Anytime. ;)
Yup, it did! Thank you! :)
Guess what? I knew all the other terms BUT dispersion forces! LOL :D
Thanks ALOT! ;D
Post by: Amelia on December 06, 2010, 07:26:15 pm
Yup, it did! Thank you! :)
Guess what? I knew all the other terms BUT dispersion forces! LOL :D
Thanks ALOT! ;D
Lol! I thought so.. but no matter.
And its okay, if you thank just one time, you know.
Post by: The Golden Girl =D on December 07, 2010, 01:05:53 pm
D here are the ppm Questions I told you about .
1. a solution is prepared by dissloving 0.475g of (NH4)2SO4 (Mr =118)in enough of distilled water and the solution is made up to 2.0 dm3
Calculate the ppm of
a] NH4 + b] SO4 2-
BOLD is the charge
If possible, please check those answers with your teacher.
Answer from My Teacher :
A] n=M/Mr
=0.475/118
=0.00403
mass =n*Mr
=0.00403*18*2
=0.145g
=1.45mg
conc=145mg/2L
= 72.5 ppm
B] Mass=0.475 - 0.145
=0.33g
=33mg
conc = 33mg/2L
=16.5ppm
=]
Post by: elemis on December 07, 2010, 01:12:02 pm
Post by: The Golden Girl =D on December 07, 2010, 01:15:16 pm
Your teacher is wrong, the Mr of Ammonium Sulphat is NOT 118. It is 132.
Ari , the Mr is Already written in the Question as 118 , Perhaps the Q is wrong ;)
Post by: The Golden Girl =D on December 07, 2010, 04:59:01 pm
can someone tell me the numbers Please ?
Thanks In Advance :)
Post by: tmisterr on December 08, 2010, 07:55:17 am
I have something to ask . My teacher said we have to know the Number of isomers of hydrocarbons from C1 to C6 just in case . So how many Isomers does a C1 to C6 each have ?
can someone tell me the numbers Please ?
Thanks In Advance :)
which class oh hydrocarbons?
Post by: Deadly_king on December 08, 2010, 09:52:30 am
I have something to ask . My teacher said we have to know the Number of isomers of hydrocarbons from C1 to C6 just in case . So how many Isomers does a C1 to C6 each have ?
can someone tell me the numbers Please ?
Thanks In Advance :)
C1 - CH4 - No other isomers
C2 - C2H6 - No other isomers
C3 - C3H8 - No other isomers
C4 - C4H10 - 2 isomers in all
C5 - C5H12 - 3 isomers in all
C6 - C6H14 - 5 isomers in all
If you have time, do take a look at the attached powerpoint presentation. It describes all what you need to know in organic chemistry. ;)
Post by: The Golden Girl =D on December 08, 2010, 11:22:22 am
C1 - CH4 - No other isomers
C2 - C2H6 - No other isomers
C3 - C3H8 - No other isomers
C4 - C4H10 - 2 isomers in all
C5 - C5H12 - 3 isomers in all
C6 - C6H14 - 5 isomers in all
If you have time, do take a look at the attached powerpoint presentation. It describes all what you need to know in organic chemistry. ;)
Jazaka Allahu Kulla kair mate ^_^
Post by: Deadly_king on December 08, 2010, 11:45:10 am
Jazaka Allahu Kulla kair mate ^_^
Rafwan Oukhtii..... :D
Post by: The Golden Girl =D on December 08, 2010, 11:48:01 am
Afwan Oukhtii..... :D
When An Arab says that you say in return Wa Jazak*
*Jazaki for a girl , Jazakom for a group :)
Afwan is mostly for when someone says Shukran/shukran Jazeelan ;)
Post by: Deadly_king on December 08, 2010, 12:28:16 pm
When An Arab says that you say in return Wa Jazak*
*Jazaki for a girl , Jazakom for a group :)
Afwan is mostly for when someone says Shukran/shukran Jazeelan ;)
Ooh thanks for the info. :D
But shukran means thanks and afwan is you're welcome, right?
Post by: Weaam on December 08, 2010, 02:51:27 pm
In june 09 Q8, i dont get why the answer is D?
And Q16 ?
And Q 17?
And Q18 ?
Need help ASAP.
Post by: elemis on December 08, 2010, 03:20:52 pm
Post by: elemis on December 08, 2010, 03:22:27 pm
Post by: The Golden Girl =D on December 08, 2010, 03:52:36 pm
Post by: The Golden Girl =D on December 08, 2010, 03:54:21 pm
Question:
In june 09 Q8, i dont get why the answer is D?
And Q16 ?
And Q 17?
And Q18 ?
Need help ASAP.
Q8] If you draw ALL of them you will notice that there are two SIMILAR groups on ONE carbon ( fi kulhom ma3ada D ) so how would you have a geometric isomers ;)
Sorry but that that's what I can do for now i gotta go -.-
Post by: elemis on December 08, 2010, 03:54:49 pm
Post by: elemis on December 08, 2010, 03:58:11 pm
The answer is A. This is because all the other options have several electrons in between the outer electron shell and nucleus. This would provide electron shielding which would reduce the first Ionisation Energy.
For answer A the only electron is being tugged on very hard by the strong force of attraction of the nucleus leading to a HIGH 1st IE.
1s1 is obviously Hydrogen.
Post by: elemis on December 08, 2010, 04:03:29 pm
1gram of ethane = 0.03448 moles
Using above equation :
0.03448 moles * 8.314 * T / p ; 0.28669*T/p
Doing the same thing for the others you should be able to determine the answer.
Post by: elemis on December 08, 2010, 04:08:46 pm
Mg2+ is the answer
Only cations will have lost electrons leading to a fall in ionic radius.
However, anions will gain electrons leading to an increase in ionic radius.
Thus we eliminate A and D.
Now we must choose between Mg and Na.
Mg has more protons than Na. Hence, Mg's nucleus has a greater positive force of attraction which works on its. electrons
When it loses its electrons this RELATIVELY larger force of attraction will attract the outer electrons inwards more than Na can. This will shrink the ionic radius EVEN MORE than Sodium.
Post by: elemis on December 08, 2010, 04:13:46 pm
Answer is A.
Bond lengths INCREASE down a group and DECREASE across a row <----- remember this.
Post by: Weaam on December 08, 2010, 05:27:11 pm
Question 16In the mark scheme, its B.
The answer is A. This is because all the other options have several electrons in between the outer electron shell and nucleus. This would provide electron shielding which would reduce the first Ionisation Energy.
For answer A the only electron is being tugged on very hard by the strong force of attraction of the nucleus leading to a HIGH 1st IE.
1s1 is obviously Hydrogen.
Post by: Weaam on December 08, 2010, 05:29:56 pm
Question 17Dude, i havent the slightest clue what you did here.
1gram of ethane = 0.03448 moles
Using above equation :
0.03448 moles * 8.314 * T / p ; 0.28669*T/p
Doing the same thing for the others you should be able to determine the answer.
I really need help on this question.
Post by: elemis on December 08, 2010, 06:06:18 pm
Dude, i havent the slightest clue what you did here.
I really need help on this question.
You need to use PV = nRT
The Ideal gas equation.
Keep plugging in the required values and see where it gets you.
P = pressure
V = volume
n = no. of moles
R = 8.314 (constant)
T = temperature in Kelvin.
I have to sleep now. Sorry. :-\
Post by: Weaam on December 08, 2010, 06:12:15 pm
Anyway, one last thing, Q23 c) (i) in January 09, i dont get how its done? why 0.01/2.00 * 100 is multiplyed by 2 ? :-\
Post by: The Golden Girl =D on December 08, 2010, 06:31:41 pm
Or i can multiply the number of moles by 24 to get the volume ?
Anyway, one last thing, Q23 c) (i) in January 09, i dont get how its done? why 0.01/2.00 * 100 is multiplyed by 2 ? :-\
As for Q 17 :
for A is going to be (12*2) + 6 = 30
B is 2*16 = 32
C is 2*19 = 38
D is just 20
n=M/Mr when Mr DECREASES, the Number of Moles INCREASES .
As for 23 , I don't get it too :-[
Hmm could you help me with Jan 2009 Q 11 , I don't get it AT ALL
Post by: Weaam on December 08, 2010, 07:09:06 pm
As for Q 17 :
for A is going to be (12*2) + 6 = 30
B is 2*16 = 32
C is 2*19 = 38
D is just 20
n=M/Mr when Mr DECREASES, the Number of Moles INCREASES .
As for 23 , I don't get it too :-[
Hmm could you help me with Jan 2009 Q 11 , I don't get it AT ALL
Q11? simple, 50cm3 of 2H2 reacts with 25cm3 of O2 to 2H2O use the mole and volume ratios 2:1:2 , 50:25:50. ;D
Post by: The Golden Girl =D on December 08, 2010, 07:11:07 pm
Q11? simple, 50cm3 of 2H2 reacts with 25cm3 of O2 to 2H2O use the mole and volume ratios 2:1:2 , 50:25:50. ;D
Ooh :-[ Okay , thanks =]
Post by: The Golden Girl =D on December 08, 2010, 07:23:45 pm
As for Q 17 :
for A is going to be (12*2) + 6 = 30
B is 2*16 = 32
C is 2*19 = 38
D is just 20
n=M/Mr when Mr DECREASES, the Number of Moles INCREASES .
Vol = N* Mr , hence the Vol increases too
As for 23 , I don't get it too :-[
Hmm could you help me with Jan 2009 Q 11 , I don't get it AT ALL
Me doing it right now :)
for the balance thingy I got it Right Alhamdulilah but for the second idk y I didn't -.-
Anyways it is solved as follows :
%error = positive or negative 0.01/2.01 *100 = positive or negative 0.498
% can NEVER be negative o.0 hence o.498 +0.498 = 0.996 rounded to =1 % which according to the MS is Right
MEASURING CYLINDER :
I did it as positive or negative 0.5/30 * 100 = positive or negative 1.67 %
which is the answer But I have NO idea y not 1.67 + 1.67 = 3.34 % as the FINAL answer
Hope I helped =]
Post by: MKh on December 08, 2010, 08:05:42 pm
Post by: Deadly_king on December 09, 2010, 11:34:43 am
who iz preparing 4 edexcel A2 unit 6B?... m preparing 4 it so cud any1 suggest me hw do i began or hw shud i sufficiently prepare 4 it? Thanks in advance
Do you mind let me know what chapter is unit 6B because am not a student of EDEXCEL. :-[
Post by: MKh on December 09, 2010, 08:28:50 pm
Post by: The Golden Girl =D on December 20, 2010, 10:27:30 am
Thanks In Advance =]
one sec
Post by: elemis on December 20, 2010, 10:30:59 am
Can Someone Please solve the attached papers and explain the details FULLY
Thanks In Advance =]
one sec
no papers attached.
Post by: The Golden Girl =D on December 20, 2010, 10:40:20 am
Anyways Hmm here are the Qs :
First it says :
delta H of Combustion of Carbon (solid state) = -394
carbon monoxide (gas state) = - 283
Hmm the Eqn as follows :
C(graphite) + 0.5 O 2 (gas) -> CO (gas)
use the data , find the Delta H of formation of carbon monoxide using Hess's Cycle .
and then the second part says :
Suggest why is it Impossible to find enthalpy change of carbon monoxide Directly ?
I wrote because it has other products as well , is that right o.0 ?!
MS's ANS : (Some) CO2 is Always produced in the reaction .
SECOND Q:
Natural Gas consists of Methane .when methane burns completely in oxygen the reaction occurs as shown below :
Bleh bleh
Methane does NOT burn Unless Lit
then A Q says :
Use this Information to explain the difference between thermodynamic and kinetic Stability
Even when the teacher explained ,I didn't Quite get it *sigh*
Post by: Amii on December 20, 2010, 11:16:44 am
-394=^Hf + (-283)
-394 + 283 = ^Hf
-111kj mol -1 =^Hf
Post by: The Golden Girl =D on December 20, 2010, 11:25:37 am
^H1=^Hf + ^H2
-394=^Hf + (-283)
-394 + 283 = ^Hf
-111kj mol -1 =^Hf
Yet Again I did a Silly Mistake in this One , can u sort of look at the rest Please :S
Post by: Amii on December 20, 2010, 11:38:46 am
and then the second part says :
Suggest why is it Impossible to find enthalpy change of carbon monoxide Directly ?
I wrote because it has other products as well , is that right o.0 ?!
MS's ANS : (Some) CO2 is Always produced in the reaction .
When you burn C in oxygen to form CO - the CO naturally gets oxidised to CO2.Hence there is always a mixture of CO and CO2 formed.
Other products formed - I am not sure if "other products" will work or not - maybe they want the answer to be more specific as to what product is formed - I am not sure :-\
Post by: Amii on December 20, 2010, 12:38:15 pm
Quote
Methane does NOT burn Unless Lit
then A Q says :
Use this Information to explain the difference between thermodynamic and kinetic Stability
Methane at room temperature will be kinetically stable ( that is the colliding particles do not hit each other with sufficient energy for the reaction to occur - activation energy is not reached[activation energy barrier is high]) and thermodynamically unstable (when energy level of products[CO2 and H20] is lower than that of reactants [CH4 and O2]),hence the reaction doesn't occur.When lit the reactants get heated and enough molecules gain energy equal to or greater than the activation energy for the system to become kinetically unstable and thermodynamically stable.Hence the reaction occurs.
GG sorry the answer is very messed up - Please check with someone else-I am really not sure :-[
Post by: The Golden Girl =D on December 20, 2010, 01:02:16 pm
When you burn C in oxygen to form CO - the CO naturally gets oxidised to CO2.Hence there is always a mixture of CO and CO2 formed.
Other products formed - I am not sure if "other products" will work or not - maybe they want the answer to be more specific as to what product is formed - I am not sure :-\
I thought so -.-
Hmm ya Okay I'll ask Ari iA =]
Thanks Loads girl =D
Post by: Amii on December 20, 2010, 01:11:08 pm
Okay :D
I thought so -.-
Hmm ya Okay I'll ask Ari iA =]
Thanks Loads girl =D
No problem :D
Post by: Deadly_king on December 20, 2010, 01:51:57 pm
When you burn C in oxygen to form CO - the CO naturally gets oxidised to CO2.Hence there is always a mixture of CO and CO2 formed.
Other products formed - I am not sure if "other products" will work or not - maybe they want the answer to be more specific as to what product is formed - I am not sure :-\
Amii is right. :)
You can never perform partial oxidation only that is the conversion of Carbon to Carbon monoxide only.
Carbon dioxide will always be present since some carbon atoms will have sufficient activation energy to undergo complete oxidation. ;)
Other products ----> I don't think it's enough to score the marks. If you intended carbon dioxide, then say so directly. Use other products in places you're not sure of.
Post by: Deadly_king on December 20, 2010, 02:05:41 pm
SECOND Q:
Natural Gas consists of Methane. When methane burns completely in oxygen the reaction occurs as shown below :
Bleh bleh
Methane does NOT burn Unless Lit
then A Q says :
Use this Information to explain the difference between thermodynamic and kinetic Stability
Here (http://chemwiki.ucdavis.edu/Physical_Chemistry/Chemical_Equilibrium/Kinetically_vs_Thermodynamically_Stable) is the exact notes you require to differentiate between thermodynamics and kinetic stability.
So we should try to understand this : Methane does NOT burn Unless Lit.
I'll take out the point which we can derive according to the quote.
1. Activation energy is not reached until we provide a source of energy when we light it up.
Let me know if you're not understanding. ;)
Post by: guMnam on December 20, 2010, 02:50:02 pm
Thanks in advance...
Post by: The Golden Girl =D on December 20, 2010, 04:11:13 pm
Here (http://chemwiki.ucdavis.edu/Physical_Chemistry/Chemical_Equilibrium/Kinetically_vs_Thermodynamically_Stable) is the exact notes you require to differentiate between thermodynamics and kinetic stability.
So we should try to understand this : Methane does NOT burn Unless Lit.
I'll take out the point which we can derive according to the quote.
1. Activation energy is not reached until we provide a source of energy when we light it up.
Let me know if you're not understanding. ;)
About the Products thing I get it ^_^
Hmm Can you Explain it in your Own words cuz I feel I'm going to be even more confused if I read All that :-X :-\ :-[
Post by: Amii on December 20, 2010, 05:09:53 pm
wats the apearance of nickel (II) sulfate crystals hydrous (I.E shape and colour) ????Green
Thanks in advance...
and
Monoclinic - I guess :-\
When I made it in school I got needle shaped crystals
Post by: The Golden Girl =D on December 20, 2010, 05:19:42 pm
Here (http://chemwiki.ucdavis.edu/Physical_Chemistry/Chemical_Equilibrium/Kinetically_vs_Thermodynamically_Stable) is the exact notes you require to differentiate between thermodynamics and kinetic stability.
So we should try to understand this : Methane does NOT burn Unless Lit.
I'll take out the point which we can derive according to the quote.
1. Activation energy is not reached until we provide a source of energy when we light it up.
Let me know if you're not understanding. ;)
Hmm can u explain it in your OWN words cuz I feel this is really complicating -.-
Post by: Deadly_king on December 21, 2010, 10:28:36 am
Hmm can u explain it in your OWN words cuz I feel this is really complicating -.-
The need for input of energy symbolizes the fact that the reaction is kinetically stable; meaning that the reaction must have some sort of energy input before it can proceed, otherwise, the reactants cannot reach the activation energy threshold.
This is how the quote 'Methane does NOT burn Unless Lit.' is related to kinetic stability, i.e activation energy is required and provided by the source of energy when we light it up. ;)
Thermodynamics is either (1) the energy released during a reaction, in which case ^G will be negative and the reaction exothermic, or (2) the energy consumed during a reaction, in which case ^G will be positive and the reaction endothermic.
Since we found that ^Hf is negative, it implies that energy is released and the reaction is exothermic.
Now we come to the difference between kinetic and thermodynamic stabilities.
A reaction is said to be kinetically stable when it requires a large activation energy. In this case we've been told that reaction does not occur unless we light it up, meaning that the reaction is kinetically stable. ;)
Something that is thermodynamically stable will not need an input of energy to be converted from reactants to products, because its most stable and preferred state is that of being composed of products. Instead, a thermodynamically-stable reaction will require energy to be converted from products back to reactants.
It's almost as if a kinetically-stable reaction is stubborn and does not want to be converted into products-- it's too lazy. You have to induce it to become products by giving it kinetic energy, which MOVES the reaction forward (kinetics = movement). The same is for thermodynamically-stable reactions, except you'd be inducing the reaction to go back into reactants from a state of products.
Post by: The Golden Girl =D on December 21, 2010, 10:32:20 am
The need for input of energy symbolizes the fact that the reaction is kinetically stable; meaning that the reaction must have some sort of energy input before it can proceed, otherwise, the reactants cannot reach the activation energy threshold.
This is how the quote 'Methane does NOT burn Unless Lit.' is related to kinetic stability, i.e activation energy is required and provided by the source of energy when we light it up. ;)
Thermodynamics is either (1) the energy released during a reaction, in which case ^G will be negative and the reaction exothermic, or (2) the energy consumed during a reaction, in which case ^G will be positive and the reaction endothermic.
Since we found that ^Hf is negative, it implies that energy is released and the reaction is exothermic.
Now we come to the difference between kinetic and thermodynamic stabilities.
A reaction is said to be kinetically stable when it requires a large activation energy. In this case we've been told that reaction does not occur unless we light it up, meaning that the reaction is kinetically stable. ;)
Something that is thermodynamically stable will not need an input of energy to be converted from reactants to products, because its most stable and preferred state is that of being composed of products. Instead, a thermodynamically-stable reaction will require energy to be converted from products back to reactants.
It's almost as if a kinetically-stable reaction is stubborn and does not want to be converted into products-- it's too lazy. You have to induce it to become products by giving it kinetic energy, which MOVES the reaction forward (kinetics = movement). The same is for thermodynamically-stable reactions, except you'd be inducing the reaction to go back into reactants from a state of products.
Jazaka Allahu Kairan =]
Post by: Deadly_king on December 21, 2010, 10:44:06 am
Jazaka Allahu Kairan =]
Wa jazaaki
Hope I said it rightly. :D
Post by: The Golden Girl =D on December 21, 2010, 10:45:34 am
Post by: Deadly_king on December 21, 2010, 10:51:03 am
Perfectly mA =D
Shukran my arabic teacher. :D
Post by: The Golden Girl =D on December 21, 2010, 11:01:05 am
Shukran my arabic teacher. :D
Al Afu =]
Post by: Uchia on December 21, 2010, 03:40:19 pm
question 18
c) iii
plz
Post by: The Golden Girl =D on December 21, 2010, 03:48:32 pm
Post by: Uchia on December 22, 2010, 02:40:48 pm
Post by: elemis on December 22, 2010, 02:46:50 pm
unit 4
What year, man ?
EDIT : Post a link to the file, please.
Post by: guMnam on December 22, 2010, 03:48:59 pm
GreenThanks i got needle too :D
and
Monoclinic - I guess :-\
When I made it in school I got needle shaped crystals
Post by: Uchia on December 24, 2010, 09:28:42 pm
Post by: Amii on December 24, 2010, 10:11:06 pm
Thanks i got needle too :DNo problem :D
Post by: Amii on December 24, 2010, 10:12:05 pm
can anyone explain to me how can we use the mass spectrometer in identifying a compound using the chart itself the one with peaks asap plzhttp://www.chemguide.co.uk/analysis/masspec/fragment.html (http://www.chemguide.co.uk/analysis/masspec/fragment.html)
http://www.knockhardy.org.uk/sci_htm_files/08msintr.pdf (http://www.knockhardy.org.uk/sci_htm_files/08msintr.pdf)
http://www.knockhardy.org.uk/sci_htm_files/08irintr.pdf (http://www.knockhardy.org.uk/sci_htm_files/08irintr.pdf)
Check these sites out - It might help :)
Post by: blackberry on December 27, 2010, 03:08:47 pm
textbook said that quantum shell is the region around the nucleus in which an electron is found
another textbook said that orbital is the region where an electron is most likely to be found and subshells are regions of differing energy within a shell, described by the letters s,p,d,f etc..
Post by: The Golden Girl =D on December 27, 2010, 06:42:08 pm
hey does nyone know the difference between quantum shells, orbitals and subshells???
textbook said that quantum shell is the region around the nucleus in which an electron is found
another textbook said that orbital is the region where an electron is most likely to be found and subshells are regions of differing energy within a shell, described by the letters s,p,d,f etc..
I explained them In the Form of Pictures , I hope My Info is right tho :S
Sorry but in the first picture the Circle that is furthest from the nucleus has only 1 electron ,and the circle around Na -the small one - isn't supposed to be there -.-
P.S. Wrote it Dow In a Hurry .
Post by: ~ Miss Relina ~ on December 27, 2010, 10:24:20 pm
Post by: The Golden Girl =D on December 28, 2010, 05:19:18 am
http://www.2dix.com/pdf-2010/as-edexcel-chemistry-practicals-pdf.php
Post by: blackberry on December 28, 2010, 01:10:10 pm
thanks for helping out!! ive attached a diagram of what i understood is a shell,subshell and orbital.
Post by: elemis on December 28, 2010, 01:22:26 pm
:P ooo sorry i shudve been more clear, actually i didnt really understand their positions in an atom!!! but i got it now!! :)
thanks for helping out!! ive attached a diagram of what i understood is a shell,subshell and orbital.
You have to understand that each quantum shell contains electron orbitals which are fuzzy areas where an electron has a high probability of being found.
These cant be drawn as 2-D shapes.
Post by: The Golden Girl =D on December 28, 2010, 02:34:33 pm
Post by: blackberry on December 28, 2010, 08:38:37 pm
Post by: NidZ- Hero on January 02, 2011, 03:40:17 pm
Post by: blackberry on January 02, 2011, 05:26:19 pm
Post by: Amii on January 02, 2011, 06:35:55 pm
where do u guys get de edxcel past papers 4rm ASAp plz replyhttps://studentforums.biz/pastpapers/edexcel-new-syllabus-biology-physics-chemistry-pastpapers!!!!!!!/ (https://studentforums.biz/pastpapers/edexcel-new-syllabus-biology-physics-chemistry-pastpapers!!!!!!!/)
http://www.freeexampapers.com/past_papers.php?l=Past_Papers/A+Level (http://www.freeexampapers.com/past_papers.php?l=Past_Papers/A+Level) - I am getting it "invalid" now - Possibly some problem - Check it again later ;)
Take care :D
Post by: The Golden Girl =D on January 02, 2011, 07:35:21 pm
where do u guys get de edxcel past papers 4rm ASAp plz reply
Hey Nidzz ,
as blackberry said I get it from Google , Plus I downloaded the files from FEP in the summer break and so I have them on my USB =]
Post by: The Golden Girl =D on January 03, 2011, 07:28:50 am
1. polar covalent where the bonding pair of electrons is nearer to one atom
2. Dispersion forces
3. Dipole/dipole forces (aka Van Der Waals): between ?+ in one molecule and ?- in another molecule.
Really Confused here , Someone Please help .
Post by: elemis on January 03, 2011, 09:55:26 am
what does this mean ?! o.0
1. polar covalent where the bonding pair of electrons is nearer to one atom
2. Dispersion forces
3. Dipole/dipole forces (aka Van Der Waals): between ?+ in one molecule and ?- in another molecule.
Really Confused here , Someone Please help .
When you consider Hydrogen Fluoride, for example, the highly electronegative fluorine attracts the bonding electrons to itself such that they stay most of the time on the Fluorine atom. Thus, a dipole-dipole moment is setup with HF becoming a polar molecule.
London Dispersion Forces = Van Der Waals forces.
Post by: The Golden Girl =D on January 03, 2011, 01:01:19 pm
Post by: elemis on January 03, 2011, 01:10:54 pm
well then what does a dipole/dipole mean ?
Basically in the above example Hydrogen has a deficiency of electrons since they maybe on the Fluoride atom. Thus Hydrogen has a positive dipole (think of it as a slight positive charge).
Fluorine has an excess of electrons and hence a negative dipole.
These are temporary dipoles and may not always exist i.e. they fluctuate in the sense the electrons are constantly moving such that may not always be on the Fluoride atom.
Post by: The Golden Girl =D on January 03, 2011, 01:14:45 pm
Basically in the above example Hydrogen has a deficiency of electrons since they maybe on the Fluoride atom. Thus Hydrogen has a positive dipole (think of it as a slight positive charge).
Fluorine has an excess of electrons and hence a negative dipole.
These are temporary dipoles and may not always exist i.e. they fluctuate in the sense the electrons are constantly moving such that may not always be on the Fluoride atom.
We call it Partially (-vely/+vely )charged .
Thanks Mate =]
Post by: Malak on January 04, 2011, 08:17:28 pm
Thx
Post by: Amii on January 04, 2011, 08:34:23 pm
What is the difference between A curly-half arrow and Full curly arrow in reaction mechanism??Hey
Thx
A half-headed or fish hook arrow represents the movement of a single electron.
Example -When light in the intiation stage splits a chlorine molecule into chlorine radicals by homolytic fission.
A full-headed curly arrow represents the movement of a pair of electrons.
Check this link out - might help
http://www.chemguide.co.uk/basicorg/conventions/curlies.html (http://www.chemguide.co.uk/basicorg/conventions/curlies.html)
Take care :D
Post by: Malak on January 05, 2011, 03:41:08 pm
Hey
A half-headed or fish hook arrow represents the movement of a single electron.
Example -When light in the intiation stage splits a chlorine molecule into chlorine radicals by homolytic fission.
A full-headed curly arrow represents the movement of a pair of electrons.
Check this link out - might help
http://www.chemguide.co.uk/basicorg/conventions/curlies.html (http://www.chemguide.co.uk/basicorg/conventions/curlies.html)
Take care :D
Oh thankyou :)
Can anyone do this question for me, Confused a bit
Q: Calculate the enthalpy change for the reaction of propanoic acid to propanal:
CH3CH2COOH + H2 --> CH3CH2CHO + H2O
Givent he following enthalpies of combustion
Propanoic acid: -1527
Hydrogen: -286
Propanal: -1821
Thanks
Post by: Amelia on January 05, 2011, 04:17:12 pm
Oh thankyou :)
Can anyone do this question for me, Confused a bit
Q: Calculate the enthalpy change for the reaction of propanoic acid to propanal:
CH3CH2COOH + H2 --> CH3CH2CHO + H2O
Givent he following enthalpies of combustion
Propanoic acid: -1527
Hydrogen: -286
Propanal: -1821
Thanks
Enthalphy change of reaction = reactants - products.
Therefore, (propanoic acid + Hydrogen) - Propanal
(-1527)+(-286) - (-1821)
Enthalphy change of reaction = +8 kjmol-1
Post by: Malak on January 05, 2011, 04:47:45 pm
Enthalphy change of reaction = reactants - products.
Therefore, (propanoic acid + Hydrogen) - Propanal
(-1527)+(-286) - (-1821)
Enthalphy change of reaction = +8 kjmol-1
Oh k thx..
By the way..Can we also use the cycle for this?
Post by: Amelia on January 05, 2011, 04:50:25 pm
Oh k thx..
By the way..Can we also use the cycle for this?
yes, the Hess's Law. Bonds broken - Bonds formed.
Post by: Uchia on January 05, 2011, 05:24:46 pm
Using IR spectroscopy, the progress of the oxidation of a primary alcohol by aqueous
acidified potassium dichromate could be followed by the change in the height of the
peak due to:
A) O–H
B) C–H
C) C–C
D) C=O
The peak due to the hydrogen nuclei in the CH2 group in the high-resolution NMR
spectrum of propanal, CH3CH2CHO, is split into which of the following number of peaks?
A)3
B)4
C)5
D)6
When a water molecule absorbs microwaves:
A there is an increase in O–H bond stretching
B there is an increase in O–H bond bending
C there is an increase in the rotation of the H2O molecule
D an O–H bond breaks
Post by: Uchia on January 05, 2011, 05:25:39 pm
The number of peaks in the low-resolution NMR spectrum of
pentan-3-one, CH3CH2COCH2CH3 is:
A 1
B 2
C 3
D 4
Post by: Deadly_king on January 06, 2011, 06:45:48 am
Also this one
The number of peaks in the low-resolution NMR spectrum of
pentan-3-one, CH3CH2COCH2CH3 is:
A 1
B 2
C 3
D 4
In low resolution NMR, peaks are formed according to the different hydrogen environment the molecule has.
In this case the answer is 2 because pent-3-one has only two H atoms in different environment namely CH3 and CH2.
For more details, click here (http://www.chemguide.co.uk/analysis/nmr/lowres.html).
Post by: Uchia on January 06, 2011, 01:34:42 pm
CH3CH2COOCH3
it is said that CH3 is an environment
CH2 is one
COO nothing
and CH3 is another one
similarly in pentan-3-one CH3CH2COCH2CH3
I think it should be 4 right or wrong
Post by: Uchia on January 06, 2011, 07:56:11 pm
I understood it now
thnxs anyways for your help
Post by: Deadly_king on January 07, 2011, 07:41:44 am
I think your answer is wrong cz according to the link you gave me it is shown that
CH3CH2COOCH3
it is said that CH3 is an environment
CH2 is one
COO nothing
and CH3 is another one
similarly in pentan-3-one CH3CH2COCH2CH3
I think it should be 4 right or wrong
Nan.........the link only gives an example on how you read an NMR spectra.
yeah yeah right sorry my mistake
I understood it now
thnxs anyways for your help
Glad you did :D
Post by: Amelia on January 08, 2011, 10:44:08 am
please help me in those questions
Using IR spectroscopy, the progress of the oxidation of a primary alcohol by aqueous
acidified potassium dichromate could be followed by the change in the height of the
peak due to:
A) O–H
B) C–H
C) C–C
D) C=O
Primary alcohol oxidises and forms, aldehydes and (further oxidation) acids.
Ans is D.
Quote
The peak due to the hydrogen nuclei in the CH2 group in the high-resolution NMR
spectrum of propanal, CH3CH2CHO, is split into which of the following number of peaks?
A)3
B)4
C)5
D)6
Ans is B
- http://chem242.wikispaces.com/Deepak+Singh's+analysis+of+the+H-NMR+of+propanal
Quote
When a water molecule absorbs microwaves:
A there is an increase in O–H bond stretching
B there is an increase in O–H bond bending
C there is an increase in the rotation of the H2O molecule
D an O–H bond breaks
Microwaves contain small amount of energy, the water molecules keep on rotating. ::)
- http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/-324719c1f8
Post by: Malak on January 08, 2011, 01:43:28 pm
Post by: Uchia on January 08, 2011, 01:48:25 pm
Post by: Amelia on January 08, 2011, 03:46:30 pm
What is a trace product?
Trace Element(s) :- A chemical element required in minute quantities by an organism to maintain proper physical functioning.
thanks a lot Amelia you were such a great help I owe you one :)
You are welcome. :)
Post by: Uchia on January 08, 2011, 05:56:07 pm
Post by: Amelia on January 08, 2011, 06:21:06 pm
hey Amelia are you doing chem A2 this jan
I did my As and A2 last june. :P
Post by: Uchia on January 09, 2011, 06:34:56 am
Post by: Amelia on January 09, 2011, 12:44:02 pm
cool I just did AS last june and it was pretty easy
All the best for your A2, then. :)
Post by: Uchia on January 10, 2011, 08:43:18 am
Post by: Malak on January 12, 2011, 01:53:20 pm
Which values of Lattice enthalpy assumes that a model is purely ionic
Theoretical or Experimental(Born-haber) ??
Thx
Post by: Weaam on January 12, 2011, 02:08:05 pm
Just confused with this..Theoretical, i think.
Which values of Lattice enthalpy assumes that a model is purely ionic
Theoretical or Experimental(Born-haber) ??
Thx
Post by: Weaam on January 12, 2011, 02:09:45 pm
Post by: Malak on January 12, 2011, 02:24:13 pm
Theoretical, i think.So Assuming that its purely ionic will result in a More exothermic value?
Post by: Weaam on January 12, 2011, 02:24:58 pm
Post by: Weaam on January 12, 2011, 02:28:16 pm
So Assuming that its purely ionic will result in a More exothermic value?No, actually, the theoritical values are always slightly less exothermic, check the past papers, they always have a question about that with the values of both so u can compare
Post by: Malak on January 12, 2011, 02:39:16 pm
And question 15 in Section B part b)(ii) and (iii) in the same paperr
B(ii) Because of the difference in ionic radius
(iii) to find the concentration in ppm, the formula is C = (Mass of component / Mass of solution) * 1000000
Therefore, first we need to find the mass of calcium M = moles * Mr
Moles is given so Mass = 0.100 * 40 = 4 g
Usign the formula C = (4 / 1000g ) * 1000000
=4000 ppm
Post by: Weaam on January 12, 2011, 02:50:00 pm
B(ii) Because of the difference in ionic radiusThankss
(iii) to find the concentration in ppm, the formula is C = (Mass of component / Mass of solution) * 1000000
Therefore, first we need to find the mass of calcium M = moles * Mr
Moles is given so Mass = 0.100 * 40 = 4 g
Usign the formula C = (4 / 1000g ) * 1000000
=4000 ppm
Post by: Malak on January 12, 2011, 03:02:27 pm
i mean how can u tell wheter its Mean bond enthalpy or bond enthalpy
thx
Post by: Weaam on January 12, 2011, 03:16:45 pm
How can you tell the difference?Bond enthalpy is when only one bond is broken, in this case only when one C-H bond is broken.
i mean how can u tell wheter its Mean bond enthalpy or bond enthalpy
thx
Mean bond enthalpy is when more than one bond is broken and the average is taken. In this case when 4 C-H bonds are broken and their average taken.
Post by: Malak on January 12, 2011, 03:44:31 pm
For me its coming out to be Fluorine :S
Post by: Malak on January 12, 2011, 04:35:41 pm
thx
Post by: xMilishax on January 12, 2011, 05:02:14 pm
Can someone please explain Question 10 in Section A of the June 2010 paper to me ?
It's C because first you find the number of moles of each of the solution by n = c x v then multiply the number of ions into the number of moles (n). A and B have 2 ions so x 2. C and D have 3 ions so x 3. A, B and D have the final answer = 2 but C = 3 so the answer is C. Hope you understand. :)
Post by: Weaam on January 12, 2011, 05:23:40 pm
It's C because first you find the number of moles of each of the solution by n = c x v then multiply the number of ions into the number of moles (n). A and B have 2 ions so x 2. C and D have 3 ions so x 3. A, B and D have the final answer = 2 but C = 3 so the answer is C. Hope you understand. :)I did thankss ;D
Quote
Can anyone help with this QIll help you with that tomorrow, cant think right now, headachee D:
thx
Post by: Weaam on January 12, 2011, 05:25:29 pm
and which one is enthalpy of reactants - enthalpy of products
Thankss
Post by: The Golden Girl =D on January 12, 2011, 08:36:54 pm
Can anyone tell me if ur calculating the enthalpy of combustion and formation which one is, enthalpy of produts - enthalpy of reactants
and which one is enthalpy of reactants - enthalpy of products
Thankss
formation ,going upwards ; FORMATION = products - reactants
Combustion , going downwards ; COMBUSTION = reactants - products
I can't seem to get what Polar and Non-Polar mean :-\ :-X
thanks in advance =]
Post by: Amii on January 12, 2011, 08:42:33 pm
I can't seem to get what Polar and Non-Polar mean :-\ :-X
thanks in advance =]
GG Check this link - might help :)
http://users.stlcc.edu/gkrishnan/polar.html (http://users.stlcc.edu/gkrishnan/polar.html)
Post by: The Golden Girl =D on January 12, 2011, 09:00:09 pm
GG Check this link - might help :)
http://users.stlcc.edu/gkrishnan/polar.html (http://users.stlcc.edu/gkrishnan/polar.html)
thanks =D
Post by: Amii on January 12, 2011, 09:17:52 pm
thanks =DNo problem
Post by: Amelia on January 13, 2011, 02:29:27 pm
Can anyone help with this Q
thx
Well according to the stoichiometric coefficient, there is only one mol of Mg in a molecule of chlorophyll. Therefore, there is
1.20 nanmol-3 of Mg present. Simply multiply the molecular mass of Mg (24.32 g/mol) by this number of moles to get your answer in grams.
Post by: Helium on January 15, 2011, 12:50:27 pm
Name and draw the following compounds,
1.CH3CHCHCH2CH(C2H5)CH3
2,CH3CH2C(CH3)2CH2CH(C3H7)CH2CH3
I can easily draw but the 6 nomenclature rules don't seem to work or
i don't get them good yet, when explaining can you say why, and whats
meant by substituent group,
Post by: Amii on January 15, 2011, 02:14:16 pm
Question plz :DCH3CHCHCH2CH(C2H5)CH3 - For this you are sure that there are two double bonds? Cause then it would be a diene :-\
Name and draw the following compounds,
1.CH3CHCHCH2CH(C2H5)CH3
2,CH3CH2C(CH3)2CH2CH(C3H7)CH2CH3
I can easily draw but the 6 nomenclature rules don't seem to work or
i don't get them good yet, when explaining can you say why, and whats
meant by substituent group,
CH3CH2C(CH3)2CH2CH(C3H7)CH2CH3
3,3-dimethyl-5-propyl heptane
2 methyl groups(removing a hydrogen atom from a molecule of methane, CH4 gives a group of atoms CH3-, called METHYL) on the 3rd carbon thus 3,3-dimethyl
1 propyl group( removing a hydrogen atom from a molecule of propane,C3H8 gives a group of atoms C3H7-, called PROPYL )on the 5th carbon thus 5-propyl
longest parent chain consists of 7 carbons - all having single bonds - hence heptane
Number the carbon atoms from the left side - cause that's how the methyl and propyl get the lowest value
methy and propyl - according to the alphabetical order
A substituent is an atom or group of atoms substituted in place of a hydrogen atom on the parent chain of a hydrocarbon - eg the methyl group or the propyl group
I hope it's correct :-\
Check this link - might help http://www.physchem.co.za/OB12-mat/organic2.htm (http://www.physchem.co.za/OB12-mat/organic2.htm)
Take care :D
Post by: Helium on January 15, 2011, 03:15:50 pm
Post by: Amii on January 15, 2011, 06:06:58 pm
THANK YOU ;DNo problem :D
Post by: Uchia on January 17, 2011, 03:37:56 pm
question 18 part c ii, iii, and iv
in edexcel unit 4 new specimen paper
I've attached the paper to
Post by: Amelia on January 18, 2011, 06:42:59 pm
plz answer the following
question 18 part c ii, iii, and iv
in edexcel unit 4 new specimen paper
I've attached the paper to
The answers are already given below the questions in the specimen paper. :-\
Post by: Uchia on January 18, 2011, 08:23:04 pm
Post by: obstacle26 on January 21, 2011, 11:07:59 pm
Can any one label it on a spectrum to make it clear?
Post by: Amelia on January 22, 2011, 04:17:07 pm
From an Infrared spectrum how to deduce where the intensity of a peak is broad,weak, medium,strong, varibale and sharp?
Can any one label it on a spectrum to make it clear?
see if these help - http://www.knockhardy.org.uk/sci_htm_files/ir2.pdf
http://www.chemguide.co.uk/analysis/ir/interpret.html
Post by: **RoRo** on January 29, 2011, 06:46:54 am
MnO4- + Fe2+ -----> Mn2+ + Fe3+
Post by: elemis on January 29, 2011, 06:54:28 am
How do you balance the following redox equation? :/
MnO4- + Fe2+ -----> Mn2+ + Fe3+
Are you sure the equation is correct ?
Post by: Amelia on January 29, 2011, 09:31:30 am
1. Write the half reactions:
Fe2+(aq) Fe3+(aq) (oxidation)
MnO4-(aq) Mn2+(aq) (reduction)
2. Balance each half reaction:
Fe2+(aq) Fe3+(aq) + e-
MnO4-(aq) + 8H+(aq) + 5e- Mn2+(aq) + 4H2O
3. Combine the half reactions to give the overall reaction:
5Fe2+(aq)-----> 5Fe3+(aq) + 5e- MnO4-(aq) + 8H+(aq) + 5e----> Mn2+(aq) + 4H2O
5Fe2+(aq) + MnO4-(aq) + 8H+(aq) 5Fe3+(aq) + Mn2+(aq) + 4H2O
Post by: **RoRo** on January 29, 2011, 10:37:33 am
I think its something like this :
1. Write the half reactions:
Fe2+(aq) Fe3+(aq) (oxidation)
MnO4-(aq) Mn2+(aq) (reduction)
2. Balance each half reaction:
Fe2+(aq) Fe3+(aq) + e-
MnO4-(aq) + 8H+(aq) + 5e- Mn2+(aq) + 4H2O
3. Combine the half reactions to give the overall reaction:
5Fe2+(aq)-----> 5Fe3+(aq) + 5e- MnO4-(aq) + 8H+(aq) + 5e----> Mn2+(aq) + 4H2O
5Fe2+(aq) + MnO4-(aq) + 8H+(aq) 5Fe3+(aq) + Mn2+(aq) + 4H2O
Thanks Amelia! :)
Post by: The Golden Girl =D on January 29, 2011, 12:20:52 pm
ex:how many Fe are in both sides and balance it and
then the Oxygens ; by adding water molecules.
then the hydrogens ; by adding H + molecules *we're assuming it's in an acidic solution*
and then the electrons ; by adding electrons -gain -> reduction.
It's confusing but u'll get the hang of it with practice =]
Post by: Amelia on January 29, 2011, 02:12:43 pm
Thanks Amelia! :)
You are welcome.
GG's tips are gonna help. ;)
Post by: **RoRo** on January 30, 2011, 12:42:26 pm
secret : look at the atoms
ex:how many Fe are in both sides and balance it and
then the Oxygens ; by adding water molecules.
then the hydrogens ; by adding H + molecules *we're assuming it's in an acidic solution*
and then the electrons ; by adding electrons -gain -> reduction.
It's confusing but u'll get the hang of it with practice =]
Alright, I'll try getting more equations and work on them, thank you!! :)
Post by: The Golden Girl =D on January 30, 2011, 04:02:59 pm
Post by: **RoRo** on February 08, 2011, 08:59:41 pm
Post by: EMO123 on February 09, 2011, 02:38:19 pm
secret : look at the atomsthanx this is also helpfull for my as levels thanxx GG
ex:how many Fe are in both sides and balance it and
then the Oxygens ; by adding water molecules.
then the hydrogens ; by adding H + molecules *we're assuming it's in an acidic solution*
and then the electrons ; by adding electrons -gain -> reduction.
It's confusing but u'll get the hang of it with practice =]
Post by: The Golden Girl =D on February 10, 2011, 01:45:43 pm
Post by: xim7007 on February 12, 2011, 03:16:08 pm
Post by: Amelia on February 13, 2011, 04:36:08 pm
How do you identify different proton environments, when a displayed structure of a compound is given. For example propan-1-ol
Propan-1-ol - CH3-CH2-CH2-OH
There are four different proton environments.
3H's in CH3 environment.
1H in OH environment.
2H's in each CH2
While using the Low NMR spectra.
When studying low-resolution proton NMR there are two things to look out for:
• The number of peaks, which gives the number of different proton environments.
• The area under each peak, which gives an idea of the number of protons (hydrogens) in each environment.
(http://i47.tinypic.com/ve6r2a.jpg)
Post by: xim7007 on February 14, 2011, 03:23:31 pm
Post by: Deadly_king on February 15, 2011, 12:37:14 pm
Thanx a lot Amelia...How do we know whether a particular group of hydrogen is a different proton environment?
You have to take a look at the neighboring carbon atom. The atoms the neighboring atom carries will identify whether the particular hydrogen is the same or different.
Example : CH4CH3Cl
Here we have two different proton environment. First in CH4, the neighboring carbon atom contains one Cl atom and 3 H atoms. Second in CH3Cl, the neighboring carbon atom carries 4 H atoms. The rest Hydrogen atoms are the same.
Have a look at this (http://www.chemguide.co.uk/analysis/nmr/lowres.html). ;)
Post by: EMO123 on February 16, 2011, 05:30:59 am
You have to take a look at the neighboring carbon atom. The atoms the neighboring atom carries will identify whether the particular hydrogen is the same or different.this are amzing notes for me as well so thanxx deadly king
Example : CH4CH3Cl
Here we have two different proton environment. First in CH4, the neighboring carbon atom contains one Cl atom and 3 H atoms. Second in CH3Cl, the neighboring carbon atom carries 4 H atoms. The rest Hydrogen atoms are the same.
Have a look at this (http://www.chemguide.co.uk/analysis/nmr/lowres.html). ;)
Post by: Deadly_king on February 16, 2011, 08:13:22 am
this are amzing notes for me as well so thanxx deadly king
Glad that the notes helped you :D
Post by: EMO123 on February 18, 2011, 03:16:48 pm
Post by: **RoRo** on February 19, 2011, 03:38:28 pm
Post by: EMO123 on February 19, 2011, 04:05:19 pm
and what is dynamic reaction that i also don't know
Post by: SauD~ on February 19, 2011, 04:15:59 pm
If a reaction reaches equilibrium the concentrations of products and concentrations of reactants remain constant.
If a reaction reaches dynamic equilibrium the concentrations of products and concentrations of reactants remain constant but both reactions are still going on, just at the same rate.
If a reaction reaches static equilibrium the concentrations of products and concentrations of reactants remain constant because the reaction has stopped.
http://uk.answers.yahoo.com/question/index?qid=20080604135124AA8ybyj :)
Post by: **RoRo** on February 19, 2011, 05:06:09 pm
An equilibrium can either be a dynamic equilibrium, where the reaction is still going on-but this might not be measureable because eventually the rate of the forward reaction will equal the rate of the backward reaction, or a static equilibrium where the reaction has completely stopped.
If a reaction reaches equilibrium the concentrations of products and concentrations of reactants remain constant.
If a reaction reaches dynamic equilibrium the concentrations of products and concentrations of reactants remain constant but both reactions are still going on, just at the same rate.
If a reaction reaches static equilibrium the concentrations of products and concentrations of reactants remain constant because the reaction has stopped.
http://uk.answers.yahoo.com/question/index?qid=20080604135124AA8ybyj :)
Thank you very much, that was very clear and helpful! :)
Post by: SauD~ on February 19, 2011, 05:17:39 pm
Thank you very much, that was very clear and helpful! :)Welcome :)
Post by: **RoRo** on February 20, 2011, 06:43:19 pm
Post by: SauD~ on February 20, 2011, 07:13:52 pm
Okai, a question, if I have a reaction where there is a gas and a liquid that is present in the reactants side and they react to give me some product, if the pressure is increased, won't this favour the forward reaction and more of the product will be produced, even though both the reactants are not gases, or is it necessary that all the reactants are gases?increasing pressure favors where less gaseous molecules are present.. remember this thing :)
it can be make out if you the reactant has more gas molecules and the product side has less molecules, the reaction will favor backward if increasing the pressure. :)
But if the reactant has less gas molecule compare to product side. increasing pressure will favor forward reaction :)
Post by: **RoRo** on February 20, 2011, 07:26:08 pm
increasing pressure favors where less gaseous molecules are present.. remember this thing :)
it can be make out if you the reactant has more gas molecules and the product side has less molecules, the reaction will favor backward if increasing the pressure. :)
But if the reactant has less gas molecule compare to product side. increasing pressure will favor forward reaction :)
Wait, you just got me confused.
Take this as an example:
N2 + 3H2 <----> 2NH3
There are more gas molecules on the reactants side than the products side, so what would increasing the pressure do and why?
So if the reactants has LESS gas molecules than the products side, increasing the pressure will do what?
Post by: Amii on February 20, 2011, 07:29:20 pm
If more no. of gas molcules on the right hand side - increasing the pressure will shift the equilibrium to the left as less no. of gas molcules.Opposite effect for decrease in pressure
If more no. of gas molcules on the left hand side - increasing the pressure will shift the equilibrium to the right. Opposite effect for decrease in pressure.
If both the sides of the equation have the same no. of gas molcules then position of the equilibrium is not affected by a change in pressure.
Suppose CH4.6H20(s) ----> CH4(g) + 6H2O (l)
<----
Reducing the pressure for this reaction will cause the equilibrium to shift to the left.As 1 gas molceule present on the right hand side of the equation but none on the left hand side.
I hope it helps :-[
Warning
LOL Saud posted before I could :D
Post by: Amii on February 20, 2011, 07:34:24 pm
Wait, you just got me confused.Increasing the pressure will cause the equilibrium to shift to the side with less no. of gas molcules - that is the right hand side for this equation - so more Ammonia formed.
Take this as an example:
N2 + 3H2 <----> 2NH3
There are more gas molecules on the reactants side than the products side, so what would increasing the pressure do and why?
So if the reactants has LESS gas molecules than the products side, increasing the pressure will do what?
Post by: **RoRo** on February 20, 2011, 07:44:47 pm
It will depend on the state of the product.And if the product is a gas - then the no. of molceules of the gas.Basically the no. of molcules of gas in each side of the equation.
If more no. of gas molcules on the right hand side - increasing the pressure will shift the equilibrium to the left as less no. of gas molcules.Opposite effect for decrease in pressure
If more no. of gas molcules on the left hand side - increasing the pressure will shift the equilibrium to the right. Opposite effect for decrease in pressure.
If both the sides of the equation have the same no. of gas molcules then position of the equilibrium is not affected by a change in pressure.
Suppose CH4.6H20(s) ----> CH4(g) + 6H2O (l)
<----
Reducing the pressure for this reaction will cause the equilibrium to shift to the left.As 1 gas molceule present on the right hand side of the equation but none on the left hand side.
I hope it helps :-[
Warning
LOL Saud posted before I could :D
Alright, thanks alot! :)
Post by: Amii on February 20, 2011, 07:47:20 pm
Decrease pressure - Equilibrium shifts to the sdie with more no. of gas molecules.
Examples -
2SO2 (g) + O2(g) ----> 2SO3 (g)
<----
Increasing the pressure will cause the equilibrium to shift to the side with less no. of gas molecules.
Right:Left
3:2
Less no. of gas moleulces on the left - so forward reaction (to the right) is favoured.More SO3 is formed.
H2 (g) +I2 (g) ---> 2HI(g)
<---
Whether you increase or drecrease the pressure the postition of the equilibrium will not be affected since the same no. of gas molecules on both the sides of the equation.
Warning again - But I already typed it so posting it :)
Post by: Amii on February 20, 2011, 07:50:22 pm
Alright, thanks alot! :)No problem :D
Take care
Post by: SauD~ on February 20, 2011, 08:22:06 pm
It will depend on the state of the product.And if the product is a gas - then the no. of molceules of the gas.Basically the no. of molcules of gas in each side of the equation.Thanks annie to be here :D
If more no. of gas molcules on the right hand side - increasing the pressure will shift the equilibrium to the left as less no. of gas molcules.Opposite effect for decrease in pressure
If more no. of gas molcules on the left hand side - increasing the pressure will shift the equilibrium to the right. Opposite effect for decrease in pressure.
If both the sides of the equation have the same no. of gas molcules then position of the equilibrium is not affected by a change in pressure.
Suppose CH4.6H20(s) ----> CH4(g) + 6H2O (l)
<----
Reducing the pressure for this reaction will cause the equilibrium to shift to the left.As 1 gas molceule present on the right hand side of the equation but none on the left hand side.
I hope it helps :-[
Warning
LOL Saud posted before I could :D
The problem is that i am in ig and used my brain from what ever i have studied... sorry man, can't be much help :(
Post by: Amii on February 20, 2011, 08:52:08 pm
increasing pressure favors where less gaseous molecules are present.. remember this thing :)You wrote the opposite thing. ;)
it can be make out if you the reactant has more gas molecules and the product side has less molecules, the reaction will favorbackwardforward if increasing the pressure. :)
But if the reactant has less gas molecule compare to product side. increasing pressure will favorforwardbackward reaction :)
Thanks annie to be here :DAtleast you tried helping :D
The problem is that i am in ig and used my brain from what ever i have studied... sorry man, can't be much help :(
+rep ;D
Post by: SauD~ on February 20, 2011, 08:57:34 pm
You wrote the opposite thing. ;)Oh!! Another silly mistake >:(
Atleast you tried helping :D
+rep ;D
i hate when i do silly mistake, i took products as reactants and vice versa >:( :'( :'(
Post by: Amii on February 20, 2011, 09:04:02 pm
Oh!! Another silly mistake >:(Doesn't matter - you can always correct yourself :D
i hate when i do silly mistake, i took products as reactants and vice versa >:( :'( :'(
Post by: Uchia on March 10, 2011, 11:00:57 am
hello
i got my chem 4 result yesterday i scored perfect hamduila
thanks for ur help
116/120
Post by: Amii on March 10, 2011, 12:19:42 pm
hey AmiiHeeyy
hello
i got my chem 4 result yesterday i scored perfect hamduila
thanks for ur help
116/120
Congratulations ;D
It wasn't me.I just gave you some you sites for mass spectrometer once.You must be talking about Amelia ;)
Take care :)
Post by: Uchia on March 10, 2011, 01:17:00 pm
::)
but still i should thank u 2 cz there was a biq guestion about the mass spectro thingii in the exam
and
Amelia ;D
Post by: Amelia on March 10, 2011, 04:48:31 pm
hey Amii
hello
i got my chem 4 result yesterday i scored perfect hamduila
thanks for ur help
116/120
You did good, mA. :)
lool ur name and her are so close i thought that it is the same person
::)
but still i should thank u 2 cz there was a biq guestion about the mass spectro thingii in the exam
and
Amelia ;D
Ahh.. that's sweet. :)
Post by: ~ Miss Relina ~ on March 11, 2011, 06:29:21 pm
How many no.of atoms present in 1 gram of ice ???and why it have larger no.of atoms i than in 1 gram of daimond???
Post by: Amii on March 11, 2011, 07:06:34 pm
well my question isOkay I am really not sure of this but will just give it a try
How many no.of atoms present in 1 gram of ice ???and why it have larger no.of atoms i than in 1 gram of daimond???
Diamond is made of up carbon, so take the molar mass of this as 12 g mol -1
Number of moles = Mass/Mr
= 1/12
= 0.083 moles
Number of atoms = 0.083* Avagodro's number
= 0.083 X 6.022*10 23
= 4.998 x 10 22 atoms
Ice means H2O
Molar mass = 2+16=18 g mol-1
Number of moles = 1/18=0.056 moles
Number of atoms = 0.056 X 6.022 *10 23
= 3.37 * 10 22 X 3 (Number of atoms in a water molecule )
=1.011 X 10 ^23
4.998 X 10^ 22 < 1.011x 10^ 23
Diamond < Ice
Take care :D
Post by: ~ Miss Relina ~ on March 11, 2011, 08:51:52 pm
Okay I am really not sure of this but will just give it a try
Diamond is made of up carbon, so take the molar mass of this as 12 g mol -1
Number of moles = Mass/Mr
= 1/12
= 0.083 moles
Number of atoms = 0.083* Avagodro's number
= 0.083 X 6.022*10 23
= 4.998 x 10 22 atoms
Ice means H2O
Molar mass = 2+16=18 g mol-1
Number of moles = 1/18=0.056 moles
Number of atoms = 0.056 X 6.022 *10 23
= 3.37 * 10 22 X 3 (Number of atoms in a water molecule )
=1.011 X 10 ^23
4.998 X 10^ 22 < 1.011x 10^ 23
Diamond < Ice
Take care :D
thnkx dear
Post by: Amii on March 11, 2011, 08:56:39 pm
thnkx dearNo probelm :D
Post by: ibuprofen500 on March 13, 2011, 07:24:00 pm
i hope someone can explain for me i tried to read about it alot but i cant seem to understand how the arrows help to predict whether a reaction will occur or no ): ?
here are examples :
Using the anti-clockwise rule:
( image attached down )
The reverse reaction is favored, so MnO2 and HCL will not react.
how did they figure out just by arrows that it will not react D: ???
Post by: Amelia on March 14, 2011, 04:17:13 pm
Hi, I would like to know how to use the anti-clockwise rule to help me predict whether a reaction will occur.
i hope someone can explain for me i tried to read about it alot but i cant seem to understand how the arrows help to predict whether a reaction will occur or no ): ?
here are examples :
Using the anti-clockwise rule:
( image attached down )
The reverse reaction is favored, so MnO2 and HCL will not react.
how did they figure out just by arrows that it will not react D: ???
Good explanation here - http://www.chemistry-react.org/go/Faq/Faq_28302.html
Post by: Blizz_rb93 on March 15, 2011, 04:44:21 pm
1) Dot & Cross Diagrams, i just want to get the basic idea of what were supposed to do here cuz sometimes they get confusing :(
2) Ionic equations, how do we write ionic equations?
Thank you =)
Post by: Amelia on March 15, 2011, 05:35:58 pm
Can anybody help me understand 2 things
1) Dot & Cross Diagrams, i just want to get the basic idea of what were supposed to do here cuz sometimes they get confusing :(
It's simple enough. ;)
Dot and Cross diagrams are used to show the electronic configuratoins of elements and ions. The elements of one element in the compund are shown by dots, those of the second element by crosses.
(http://www.webchem.net/images/bonds/covale5.gif)
Quote
2) Ionic equations, how do we write ionic equations?
Thank you =)
Here - http://wiki.answers.com/Q/How_do_you_write_a_net_ionic_equation
Post by: SoONa on March 15, 2011, 08:01:07 pm
thanks in advance
Post by: The Golden Girl =D on March 16, 2011, 03:04:15 pm
Hey ... so i really need to know what experiments and subjects i need to know for unit 3 ?????
thanks in advance
Check here :
http://answers.yahoo.com/question/index?qid=20100501124330AALLukc
http://knowledgeoman.com/forums/archive/index.php/t-9292.html
http://www.drbateman.net/asa2chem.htm
http://knowledgeoman.com/forums/showthread.php?9292-Edexcel-Chemistry-unit-3B-help-needed!
a Book if you want :
http://www.bookdepository.co.uk/book/9781444108439/Edexcel-ASA-level-Chemistry-Unit-3-and-6
I hope it helps :)
Post by: SoONa on March 16, 2011, 03:23:26 pm
Post by: The Golden Girl =D on March 16, 2011, 05:18:00 pm
Thank UUUUUUUUU it definetly helps ;D i see the light now :P
LOL :D your welcome :D
Post by: Blizz_rb93 on March 16, 2011, 05:46:35 pm
right now i need some help in the moles section, and everything related to it
thank you
Post by: Amelia on March 16, 2011, 06:35:27 pm
can anyone let me know good websites for chemistry??
right now i need some help in the moles section, and everything related to it
thank you
Check these - http://www.chemguide.co.uk/
http://www.docbrown.info/page04/4_73calcs.htm
I hope they help. :)
Post by: EMO123 on March 16, 2011, 07:11:10 pm
the home page
Post by: ~ Miss Relina ~ on March 17, 2011, 11:30:50 pm
Post by: elemis on March 18, 2011, 03:18:18 am
are we supposed to know formation of nitric acid , extraction and electrolysis of aluminium ,electrolysis of brine to form clorine in the new edxecel specification of as-level or not [plz reply to me soon
Download the syllabus : http://www.edexcel.com/migrationdocuments/GCE%20New%20GCE/International-spec-Chemistry.pdf (http://www.edexcel.com/migrationdocuments/GCE%20New%20GCE/International-spec-Chemistry.pdf)
Post by: **RoRo** on March 18, 2011, 02:55:03 pm
& does a shorter bond mean that there's more attraction between the two atoms and that more energy will be required to separate them?
Post by: Amelia on March 18, 2011, 04:13:05 pm
In hybridization, when considering ethene, the C=C has a sigma bond formed by sp3-sp3 overlap and a pi bond formed by sp2-sp2 overlap, does the pi bond bring the two atoms closer to each other and hence the bond length of C=C becomes less than that of C-C?
& does a shorter bond mean that there's more attraction between the two atoms and that more energy will be required to separate them?
A double bond is composed of one single sp-sp bond and a second pi-pi bond, the first bond is already holding the atoms together, the pi-pi bond increases the strength of the bond and so draws the atoms closer together. This also results in the sp-sp bond strengthening as orbital overlap increases.
Greater the attraction between the nuclei and the electrons smaller will be the distance between them and so, yes; the double bond requires more energy to seperate them.
Post by: **RoRo** on March 18, 2011, 06:57:14 pm
A double bond is composed of one single sp-sp bond and a second pi-pi bond, the first bond is already holding the atoms together, the pi-pi bond increases the strength of the bond and so draws the atoms closer together. This also results in the sp-sp bond strengthening as orbital overlap increases.
Greater the attraction between the nuclei and the electrons smaller will be the distance between them and so, yes; the double bond requires more energy to seperate them.
Okay, thank you! :)
May I just confirm one more thing?
The products of incomplete combustion, I recall from IG's that it was carbon monoxide and water, but in my edexcel AS chemistry textbook, it says carbon [soot], carbondioxide and carbonmonoxide, so which one is right?
Post by: The Golden Girl =D on March 18, 2011, 06:59:13 pm
carbon soot is for ANY type of combustion ;)
Based on my knowledge.
Post by: Amelia on March 18, 2011, 07:50:07 pm
Okay, thank you! :)
May I just confirm one more thing?
The products of incomplete combustion, I recall from IG's that it was carbon monoxide and water, but in my edexcel AS chemistry textbook, it says carbon [soot], carbondioxide and carbonmonoxide, so which one is right?
Both of them are right. Incomplete combustion can produce Soot, or Carbon (C). Carbon Dioxide. Carbon Monoxide (our poisonous gas) and water vapour
C2H2 (g) + O2 (g) --> H2O (g) + CO2 (g) + CO (g) + C (s) This is the incomplete combustion of acetylene.
Incomplete combustion -> CO and water as well as carbon soot
carbon soot is for ANY type of combustion ;)
Based on my knowledge.
()
Post by: elemis on March 19, 2011, 03:45:21 am
Incomplete combustion -> CO and water as well as carbon soot
carbon soot is for ANY type of combustion ;)
Based on my knowledge.
However, the primary product is CO NOT CO2. CO2 is formed but in very minute quantities.
Post by: Deadly_king on March 19, 2011, 01:54:38 pm
Okay, thank you! :)
May I just confirm one more thing?
The products of incomplete combustion, I recall from IG's that it was carbon monoxide and water, but in my edexcel AS chemistry textbook, it says carbon [soot], carbondioxide and carbonmonoxide, so which one is right?
All three of them are correct. ;)
You can never say a reaction is altogether incomplete. That's why all three products can be present. Soot(carbon) is present since some of it has not combusted yet..............some have been converted to carbon monoxide only while others have already been converted to carbon dioxide. :D
Post by: ~ Miss Relina ~ on March 21, 2011, 11:19:39 am
Post by: elemis on March 21, 2011, 01:46:12 pm
plz explain why it is not D
The prefix Z is used to denote a CIS molecule.
In this case it is a TRANS Geometric isomer thus, the prefix E is used i.e. E 2-chlorobut-2-ene
Post by: ~ Miss Relina ~ on March 21, 2011, 02:05:10 pm
The prefix Z is used to denote a CIS molecule.well how come ???
In this case it is a TRANS Geometric isomer thus, the prefix E is used i.e. E 2-chlorobut-2-ene
u know here there is chlorine so we could not use the cis-trans model so we must use the E-Z model and if we use it it would be D as clorine has higher priority than ccarbon and methyl group and in ''up'' position while hyrogen due to its lower atomic no. has lower priority to carbon and methyl group so higher priority groups are in ''up'' postion so both higher priority groups are in ''up''position so z-2-chloro bute-2-ene???
are u convinced or not yet??
Post by: Amii on March 21, 2011, 05:45:12 pm
well how come ???You are right.It should be D.Even in my text book this structure has a name Z-2-chlorobut-2-ene.
u know here there is chlorine so we could not use the cis-trans model so we must use the E-Z model and if we use it it would be D as clorine has higher priority than ccarbon and methyl group and in ''up'' position while hyrogen due to its lower atomic no. has lower priority to carbon and methyl group so higher priority groups are in ''up'' postion so both higher priority groups are in ''up''position so z-2-chloro bute-2-ene???
are u convinced or not yet??
The answer C has to be wrong. :-\
Post by: ~ Miss Relina ~ on March 21, 2011, 09:00:33 pm
You are right.It should be D.Even in my text book this structure has a name Z-2-chlorobut-2-ene.oh Thanks dear for ur reply, but which textbook is that i'm really curios about it ;)
The answer C has to be wrong. :-\
and i'll still wait for Ari Ben Canaan reply so that i would like to know his reasons for choosing that answer D. :)
Post by: Amii on March 21, 2011, 10:08:27 pm
oh Thanks dear for ur reply, but which textbook is that i'm really curios about it ;)No problem
and i'll still wait for Ari Ben Canaan reply so that i would like to know his reasons for choosing that answer D. :)
George Facer AS Chemistry
Take care :D
Post by: elemis on March 22, 2011, 02:31:32 pm
well how come ???
u know here there is chlorine so we could not use the cis-trans model so we must use the E-Z model and if we use it it would be D as clorine has higher priority than ccarbon and methyl group and in ''up'' position while hyrogen due to its lower atomic no. has lower priority to carbon and methyl group so higher priority groups are in ''up'' postion so both higher priority groups are in ''up''position so z-2-chloro bute-2-ene???
are u convinced or not yet??
YIKES !! My bad. You're correct.
Post by: ~ Miss Relina ~ on March 22, 2011, 02:33:48 pm
No problemomg that a good book i think i am really feeling totally confused who is right??
George Facer AS Chemistry
Take care :D
Post by: ~ Miss Relina ~ on March 22, 2011, 02:34:31 pm
Post by: Amii on March 22, 2011, 04:42:27 pm
aah I have another question about choosing the titres to get the mean titre what do u depend on to choose ??? and if the burrete uncertainty is +/_ 0.05 so what would be the actual vale between if we have for example 14.85 cm3 my techer told me it would be between (14.75cm3 & 14.95cm3) but my answer was (14.80cm3 &14.90cm3) so help me with that issue plzError for each reading = +/-0.05cm3
Error in the titre = +/- 0.1 cm3 (0.05X2)
14.85 + 0.1 =14.95 cm3
14.85 - 0.1 =14.75 cm3
:D
Post by: ~ Miss Relina ~ on March 23, 2011, 11:37:25 am
Error for each reading = +/-0.05cm3is this is a standard used for any example like that ???
Error in the titre = +/- 0.1 cm3 (0.05X2)
14.85 + 0.1 =14.95 cm3
14.85 - 0.1 =14.75 cm3
:D
Post by: ~ Miss Relina ~ on March 23, 2011, 11:38:17 am
Post by: The Golden Girl =D on March 23, 2011, 11:40:19 am
Post by: ~ Miss Relina ~ on March 23, 2011, 10:46:27 pm
Post by: Blizz_rb93 on March 24, 2011, 10:08:54 am
it says
Will the reactions of 24Mg and 23Mg with oxygen be any different? If so, how? If not, why?
Thank you :)
Post by: Amii on March 24, 2011, 06:14:33 pm
this is from the chemistry as revision guide, its one of the thinking task
it says
Will the reactions of 24Mg and 23Mg with oxygen be any different? If so, how? If not, why?
Thank you :)
They are isotopes - with different number of neutrons but same number of electrons and protons . Same electronic configuration means identical chemical reactions.
Not sure though :-\
Post by: Amii on March 25, 2011, 12:52:23 pm
Volume of gas = moles X molar volume
Units of both the volumes should be the same,both must be either dm3 or cm3.
Molar volume = 24 dm3 mol-1 = 24 000 cm3 dm -1
Number of moles of Hydrogen Sulfie = 500/24000 = 0.02083 moles
H2S : H20
2 : 2
0.0208 : x
x= 0.208 moles of H20
Volume of H20 = 0.0208X 24000= 500 cm3
If you want do the calculations in dm3 then convert the the volumes which are in cm3 to dm3 by dividing it by 1000(1dm3=1000cm3) and take the molar volume as 24 dm3 mol-1.
Take care :D
Post by: Amii on March 25, 2011, 01:17:08 pm
Post by: Blizz_rb93 on March 25, 2011, 01:22:36 pm
Where did the question go? ::)I removed it before you posted the question cause I wanted to ask another question but still thank you for your answer!! I didn't notice you were posting the answer so when I figured it out on my own I removed it thats why.
Post by: Amii on March 25, 2011, 01:33:32 pm
I removed it before you posted the question cause I wanted to ask another question but still thank you for your answer!! I didn't notice you were posting the answer so when I figured it out on my own I removed it thats why.Oh okay.No problem :D
Post by: ~ Miss Relina ~ on March 25, 2011, 01:42:06 pm
Post by: Amii on March 25, 2011, 02:03:52 pm
does HCl contain permanent dipole-dipole between its molecules ???Yes.HCl is a polar molecule,hence it will have permanent dipole-dipole as well as instantaneous induced dipole-induced dipole intermolecular forces between its molecules.
http://www.chemguide.co.uk/atoms/bonding/vdw.html (http://www.chemguide.co.uk/atoms/bonding/vdw.html) This might help :)
Take care :D
Post by: elemis on March 25, 2011, 02:28:09 pm
does HCl contain permanent dipole-dipole between its molecules ???
Although it has permanent dipole-dipole forces between molecules the DOMINANT intermolecular force is Hydrogen bonding.
Post by: Amii on March 25, 2011, 03:29:26 pm
Although it has permanent dipole-dipole forces between molecules the DOMINANT intermolecular force is Hydrogen bonding.There can not be hydrogen bonding between HCl molecules.Hydrogen bonding can only occur between an electropositive hydrogen atom and an electronegative oxygen,nitrogen or fluorine atom.
Chlorine atoms are too large to form hydrogen bonds.
Post by: The Golden Girl =D on March 25, 2011, 03:32:19 pm
Post by: Blizz_rb93 on March 25, 2011, 06:47:22 pm
2NH3 (aq) + H2SO4 (aq) --> (NH4)SO4 (aq)
Calculate the theoretical maximum yield that can be obtained by reacting 25.0 cm3 of 2.0mol dm-3 ammonia solution with an excess of sulfuric acid
Post by: Amii on March 25, 2011, 07:32:06 pm
=2 X (25/1000) [1dm3=1000cm3)
=0.05 moles of ammonia
NH3 : (NH4)2SO4
2 : 1
0.05 : x
x = 0.05/2 = 0.025 moles of ammonium sulfate
Molar mass of (NH4)2SO4 = 132.1 g mol-1
Mass = 132.1 X 0.025
=3.3025 g
Post by: Blizz_rb93 on March 25, 2011, 08:17:27 pm
Really appreciate it! :D
+rep :D
Post by: Amii on March 26, 2011, 06:33:52 am
Thank you!!! =)No problem :D
Really appreciate it! :D
+rep :D
Post by: Blizz_rb93 on March 26, 2011, 01:41:58 pm
b) If the yield of the electrolysis plant is 90%, what mass of the oxide must be used to produce 1 tonne of aluminium?
how do we find out in (a) the percentages of each element in the compound??
Post by: elemis on March 26, 2011, 01:51:38 pm
a) Aluminium is extraced by electrolysis of Al2O3. What is the maximum mass of the metal that could be obtained from 1 tonne of the oxide?
b) If the yield of the electrolysis plant is 90%, what mass of the oxide must be used to produce 1 tonne of aluminium?
how do we find out in (a) the percentages of each element in the compound??
2Al2O3 ----> 4Al + 3O2
1 tonne of bauxite = 9.80 * 10-3 moles
Hence, 1 tonne of bauxite gives 0.0196 moles of Al metal i.e. 0.529 tonnes of Aluminum.
Post by: elemis on March 26, 2011, 01:57:38 pm
1/x = 0.9
x = 1.11 tonnes of Al.
Now use the molar ratios to find the mass of bauxite. Make sure to convert 1.11 tonnes of Al to moles when using the ratio !
Post by: Blizz_rb93 on March 26, 2011, 02:06:44 pm
Post by: elemis on March 26, 2011, 02:19:37 pm
how did you find out the moles of bauxite?? :S I dont understand
First, I wrote the equation. Then I balanced it.
We are told we want 1 tonne of the metal.
Thus, moles = mass/molar mass
moles = 1/molar mass of bauxite
moles = 9.80 * 10-3 moles
Post by: Blizz_rb93 on March 26, 2011, 02:33:08 pm
i figured out i was making a mistake in the calculations :p
for the molar mass, instead of putting 27 for the Al, i used 23 xD mixed it up with sodium for some reason :p
anyways thank you!! :D
Post by: **RoRo** on April 01, 2011, 06:03:19 pm
If we're asked to give all the possible products of the following reaction:
CH3CH=CH2 ----Br2 [on top of the arrow] and NaCl [at the bottom of the arrow]---->
What would the answer be? According to my teacher's explanation it should be like this: CH3CH(Br)CH2(Br) and CH3CH(Cl)CH2(Br) but what I wrote in my book in the class was this: CH3CH(Br)CH2(Br) and CH3CH(Br)CH2(Cl), so I wanted to confirm which one is right?
Thanks in advance! :)
Post by: elemis on April 01, 2011, 06:09:44 pm
I have a question in Organic Chemistry - addition reactions of alkenes.
If we're asked to give all the possible products of the following reaction:
CH3CH=CH2 ----Br2 [on top of the arrow] and NaCl [at the bottom of the arrow]---->
What would the answer be? According to my teacher's explanation it should be like this: CH3CH(Br)CH2(Br) and CH3CH(Cl)CH2(Br) but what I wrote in my book in the class was this: CH3CH(Br)CH2(Br) and CH3CH(Br)CH2(Cl), so I wanted to confirm which one is right?
Thanks in advance! :)
You are both correct.
Post by: **RoRo** on April 01, 2011, 06:56:46 pm
You are both correct.
How come?
See, that's what I understood, correct me if I'm wrong! :)
In CH3CH=CH2, the alkyl group is present on the LHS so it electrons are pushed to the RHS due to the Induction effect, so a carbocation is formed at the LHS and so Br+ which is more reactive than Na+ will attach to the slightly negatively charged carbon atom i.e. the one of the RHS and now what's left is the Br- and the Cl-, so they'll have to attach to the carbocation which is positively charged since they are negatively charged, right? & not on the RHS where the carbon atom is negatively charged.
& also, another question:
What was the original alkene before it got oxidised in the presence of hot acidic KMnO4 and produced CO2 + CH3COCH2CH3 + CH3COCH3 + CH3COOH + H2O?
Post by: The Golden Girl =D on April 02, 2011, 10:12:22 am
About ethanoic acid ,I'm not sure.
Water and sodium is the Most vigorous reaction here Since Na is in group 1 and all metals in group 1 react vigorously with water.
I hope I helped :)
Post by: **RoRo** on April 02, 2011, 04:27:42 pm
I know that ethanol is an inert solvent so it would be the reaction which is taking place with Most ease.
About ethanoic acid ,I'm not sure.
Water and sodium is the Most vigorous reaction here Since Na is in group 1 and all metals in group 1 react vigorously with water.
I hope I helped :)
Actually the answer according to my teacher was that it's easier with the acid, then with water then with alcohol, she had even told us the reasoning, but I haven't noted it down clearly! :/
Post by: **RoRo** on April 03, 2011, 10:31:20 am
Post by: The Golden Girl =D on April 03, 2011, 03:25:14 pm
& my 4th questions is: Do we need to learn the wavenumbers for the different bonds in the different functional groups in IR mass spectroscope?
Based on my teacher you have to know some essential ones in case they're not given ;)
Post by: Vampire-Love4ever on April 04, 2011, 07:17:15 pm
PLEASE HELP!!!!!!!!!!
Post by: **RoRo** on April 05, 2011, 10:25:20 am
Based on my teacher you have to know some essential ones in case they're not given ;)
Like?
Post by: The Golden Girl =D on April 05, 2011, 12:47:01 pm
Like?
I'm sorry I think I wrote that while daydreaming... My teacher says that they'll be given you don't have to memorize * they're A LOT , I tried to memorize but I easily forgot them :-\ * ...
P.S. No you don't need to ;)
Post by: **RoRo** on April 05, 2011, 02:16:29 pm
I'm sorry I think I wrote that while daydreaming... My teacher says that they'll be given you don't have to memorize * they're A LOT , I tried to memorize but I easily forgot them :-\ * ...
P.S. No you don't need to ;)
hahaha :D It's okay! :)
Post by: ~ Miss Relina ~ on April 06, 2011, 02:31:22 pm
Post by: Amii on April 06, 2011, 02:50:16 pm
Check this link please - It might help
Take care :D
Post by: Blizz_rb93 on April 06, 2011, 03:13:03 pm
is there anything that could help me when i want to write down the equation for a reaction in which the enthalpy change is the standard enthalpy change of combustion
like for example,
C2H6 (g) ; C2H6 (g) + 7/2 O2 (g) --> 2CO2 (g) + 3H2O (l)
like how would we come up with the products?? i know this might be a stupid question or something lol but im studying chemistry AS all alone without any teachers since our teacher last year didn't cover the material for us so yeah =/
anyways i'd appreciate any help!! thank you =)
Post by: The Golden Girl =D on April 06, 2011, 03:25:59 pm
I have this question regarding the standard enthalpy change of combustion
is there anything that could help me when i want to write down the equation for a reaction in which the enthalpy change is the standard enthalpy change of combustion
like for example,
C2H6 (g) ; C2H6 (g) + 7/2 O2 (g) --> 2CO2 (g) + 3H2O (l)
like how would we come up with the products?? i know this might be a stupid question or something lol but im studying chemistry AS all alone without any teachers since our teacher last year didn't cover the material for us so yeah =/
anyways i'd appreciate any help!! thank you =)
I don't get your question :-X
Post by: Blizz_rb93 on April 06, 2011, 03:31:35 pm
CH3OH (l) and they want us to write an equation for the reaction in which the enthalpy change is the standard enthalpy change of combustion
What i wanna know is how do we write the equation? how do we know what the products in the reaction are? I know that CH3OH will react with O2 as it is a combustion reaction so yeah =p
Post by: The Golden Girl =D on April 06, 2011, 03:35:28 pm
Like ok they give us
CH3OH (l) and they want us to write an equation for the reaction in which the enthalpy change is the standard enthalpy change of combustion
What i wanna know is how do we write the equation? how do we know what the products in the reaction are? I know that CH3OH will react with O2 as it is a combustion reaction so yeah =p
I think you want me to tell ou how to know what the product is ?
in that case in ALL combustion reactions the products are CO2 and H2O ....that's a MUST .... I suggest you give us examples of reactions in which you were not able to know what the products are cuz that'll it make it easy for us to help :)
Post by: Blizz_rb93 on April 06, 2011, 03:43:36 pm
Post by: The Golden Girl =D on April 06, 2011, 05:24:59 pm
Post by: Amii on April 06, 2011, 05:44:16 pm
Post by: Blizz_rb93 on April 07, 2011, 05:04:17 pm
H2SO4 (l) + 2KCl (s) -> 2HCL (g) + K2SO4 (s)
Given the information:
H2SO4 (l) + 2KOH (s) -> K2SO4 (s) + 2H2O (l) ; Enthalpy change under standard conditions = -342kJ
HCl (g) + KOH (s) -> KCl (s) + H2O (l) ; Enthalpy change under std. conditions = -204 kJ
calculate the standard enthalpy change for the formation of hydrogen chlodirde from potassium chloride and concentrated sulfuric acid.
Post by: elemis on April 07, 2011, 05:39:14 pm
I want to see if you attempted this problem.
Post by: Blizz_rb93 on April 08, 2011, 02:51:45 pm
H2SO4 (l) + 2KCl (s) -> 2HCl (g) + K2SO4 (s)
Given that : H2SO4 (l) + 2KOH (s) -> K2SO4 (s) + 2H2O (l) ; enthalpy change = -342 kJ
and HCl (g) + KOH (s) -> KCl (s) + H2O (l) ; enthalpy change = -204 kJ
for the 2nd equation;
we put the products on the reactants side and the reactants on teh products sign
=> KCl (s) + H2O (l) -> HCl (g) + KOH (s) and multiply each element by 2
=> 2KCl (s) + H2O (l) -> 2HCl (g) + 2KOH (s) ; so the enthalpy change right now is 204x2
the negative sign turns to positive as we reversed the equation
so the enthalpy change of reactoin wud be = -342 + (2x204) = 66kJ
i know that we wud have to multiply the 2nd reaction so that some parts of it wud be cancelled but im really confused=/ i just wanna know what are the STEPS we are required to know and how do we do these steps
Thank you
Post by: Blizz_rb93 on April 08, 2011, 03:40:19 pm
Post by: Blizz_rb93 on April 08, 2011, 06:53:53 pm
a) C2H4 (g) + H2 (g) --> C2H6 (g)
The enthalpy change of this reaction can be found by experiment to be -136 kJ/mol. Calculate the enthalpy change using the mean bond enthalpies given in book.
C-C = 347 / C-H = 413 / C=C = 612 / H-H = 436
now here's my answer to this
1 x (C=C) + 4 x (C-H) + 1 x (H-H) -> (612) + (4 x 413) + (436) = 2700
now for the products side -> 6 x (C-H) + 1 x (C-C) = 2825
2700 - 2825 = -125 kJ/mol ; exothermic reaction
so is that right? i just wanna doublecheck here
now for b)
The values will be different, why is this??
I was assuming it could be due to some experimental errors or heat loss ? is that right? either way what would your answer be?
Thank you! =)
Post by: elemis on April 09, 2011, 08:55:20 am
1)
a) C2H4 (g) + H2 (g) --> C2H6 (g)
The enthalpy change of this reaction can be found by experiment to be -136 kJ/mol. Calculate the enthalpy change using the mean bond enthalpies given in book.
C-C = 347 / C-H = 413 / C=C = 612 / H-H = 436
now here's my answer to this
1 x (C=C) + 4 x (C-H) + 1 x (H-H) -> (612) + (4 x 413) + (436) = 2700
now for the products side -> 6 x (C-H) + 1 x (C-C) = 2825
2700 - 2825 = -125 kJ/mol ; exothermic reaction
so is that right? i just wanna doublecheck here
now for b)
The values will be different, why is this??
I was assuming it could be due to some experimental errors or heat loss ? is that right? either way what would your answer be?
Thank you! =)
Yeah, your method is correct and so is your calculation.
However, for the b part you are wrong. The data booklet quotes MEAN bond enthalpies. That is, they have found the average bond eenrgy for C-H bond.
Thus, the actual value of the C-H bond in ethene or ethane might be differ from the MEAN bond energy.
This why there is a difference.
Post by: Blizz_rb93 on April 09, 2011, 09:45:41 am
+rep
Post by: Blizz_rb93 on April 10, 2011, 07:37:39 pm
a) CH3(CH2)2Cl
b) CH3C(CH3)2CH(CH3)CH3
:S i really dont know how to write it down
when the (CH2)2 does that mean that theres two CH2 branches ??
and can someone show me the answers of both so i can double check my work?
Post by: Shazizzzle on April 10, 2011, 10:02:00 pm
1. Name and write out the full structural formulae for the following compounds :Yes, the (CH2)2 means there are two CH2.
a) CH3(CH2)2Cl
b) CH3C(CH3)2CH(CH3)CH3
:S i really dont know how to write it down
when the (CH2)2 does that mean that theres two CH2 branches ??
and can someone show me the answers of both so i can double check my work?
See the image attached. I've written both the structural formula, as well as the displayed one, for better understanding.
Post by: Blizz_rb93 on April 11, 2011, 03:46:09 pm
Yes, the (CH2)2 means there are two CH2.Thank you =)
See the image attached. I've written both the structural formula, as well as the displayed one, for better understanding.
Post by: Shazizzzle on April 11, 2011, 05:37:43 pm
I really need the answer to Q4 b) (iii) and (iv)on page 253 please, thanks. :)
Post by: Aadeez || Zafar on April 11, 2011, 06:30:17 pm
1. Name and write out the full structural formulae for the following compounds :
a) CH3(CH2)2Cl
b) CH3C(CH3)2CH(CH3)CH3
:S i really dont know how to write it down
when the (CH2)2 does that mean that theres two CH2 branches ??
and can someone show me the answers of both so i can double check my work?
(CH2) means R---CH2--CH2----R
FOR EXAMPLE : -CH3(CH2)5CHClCH3
WOULD MEAN
CH3----CH2----CH2----CH2----CH2----CH2--CHCl--CH3
naming - 2-chloro-octane
Post by: Aadeez || Zafar on April 11, 2011, 06:32:02 pm
Thank you =)if still any problem
then watch videos of khanadcademey.org (ORGANIC CHEMISTRY PLAYLIST)
u know it perfectly
Post by: EMO123 on April 12, 2011, 08:32:13 am
if still any problemkhan academy has got many more videos also so watch it all of chemistry also
then watch videos of khanadcademey.org (ORGANIC CHEMISTRY PLAYLIST)
u know it perfectly
Post by: Blizz_rb93 on April 12, 2011, 02:23:02 pm
Post by: Master_Key on April 12, 2011, 02:25:41 pm
Explain why the different fractions of crude oil are collected at different temperatures?
The chains of hydrocarbon are of different lengths so they have different boiling points and thus are separated at different temperatures.
Post by: ~ Miss Relina ~ on April 12, 2011, 02:25:53 pm
Explain why the different fractions of crude oil are collected at different temperatures?
due to different boiling points for each fraction so differnt volatility so fractions are collected faster than other due to weaker :)forces
Post by: Shazizzzle on April 12, 2011, 08:42:05 pm
Explain why the different fractions of crude oil are collected at different temperatures?
The boiling points of hydrocarbons depend on the intermolecular forces between the hydrocarbon molecules. They have simple van der waals forces between them.
As the hydrocarbons get larger, their Mr, size, and the total number of electrons increase, and therefore the van der waals forces between them get stronger, and so more energy is needed to 9vercome those stronger forces and hence the increasing boiling point. :)
Simply, more electrons, stronger intermolecular forces, higher boiling and melting points.
Post by: moalna on April 13, 2011, 09:32:15 am
i have a question
why do we have to add the sulphuric acid slowly when preparing the bromoalkane from alcohol?
I think thats because the reaction is exothermic and it is done to prevent over heating. If you add slowly, most of the heat generated will be lost to the surrounding and the mixture container will cool down a little bit before you add the next drop of sulphuric acid. If you add it quickly, the effect of the heat generated will be too much.
Post by: ~ Miss Relina ~ on April 13, 2011, 01:11:45 pm
Post by: The Golden Girl =D on April 13, 2011, 01:13:44 pm
how to decide whether the last answer to any question would be whether 2/3/4 s.f.?
My teacher tells me write it in 3 s.f. to be on the safe side :)
Notice sometimes in the Questions they ask for 2 s.f. or 3s.f. ,in that case you write it down in the form they asked ;)
Post by: Master_Key on April 13, 2011, 02:37:17 pm
how to decide whether the last answer to any question would be whether 2/3/4 s.f.?
Read the first page of your exam paper. It specifies to write to any s.f.
In CIE GCE AS/A Level - Maths - 9709.
Give non-exact numerical answers correct to 3 significant figures, or 1 decimal place in the case of angles in
degrees, unless a different level of accuracy is specified in the question.
Post by: red_911 on April 13, 2011, 05:34:27 pm
like shouldnt it be +3+ -2*3 = -3 ???
Post by: elemis on April 13, 2011, 05:45:55 pm
its a silly question but i dont understand how valency of nitrate (NO3) is -1
like shouldnt it be +3+ -2*3 = -3 ???
Nitrogen can have variable valencies. In this case it is 5.
Hence, 5-6=-1
Post by: **RoRo** on April 13, 2011, 06:25:22 pm
Can someone please confirm for me which one is the right one?
Version #1:
Carboxylic Acids > Sulphonic Acid > Acid Anhydride > Esters > Acyl halide> Amide > Aldehyde > Ketones > Nitriles > Alcohols > Amino > Ethers > Alkenes > Alkynes > Substituents
Version #2:
Carboxylic Acids > Sulphonic Acids > Acid Anhydride > Esters > Acyl Halides > Amides > Nitriles > Aldehydes > Ketones > Alcohols > Amines > Alkyne > Alkene
Version #3:
The one I'm finding online here: http://www.chem.ucalgary.ca/courses/351/orgnom/functional/func.html
-----------------------------------------------------------
Question 2: How do you name this compound?
CH3CH(SO3H)=CH2COOH
Is it 3-Sulphobutanoic acid OR 3-Sulphobutan-2-oic acid?
-----------------------------------------------------------
Question 3: If we have a compound like this: NH2-CH2-CH2-CH2-CH2-NH2 does it make a difference if we name it 1,4-Butanediamine OR Butane-1,4-diamine?
Post by: Blizz_rb93 on April 14, 2011, 05:29:21 am
Post by: elemis on April 14, 2011, 05:50:21 am
How the presence of a double bond affects the physical and chemical properties of the alkenes?
Chemically they tend to react via an electrophilic mechanism.
Physical properties.... look it up in your textbook.
Post by: Blizz_rb93 on April 14, 2011, 10:14:28 am
Post by: elemis on April 14, 2011, 10:30:49 am
How does the reaction of the alkenes with the halogens differ from the reaction of the alkanes with the halogens?
This rather elemetary stuff, open your textbook and read.
Post by: Aadeez || Zafar on April 14, 2011, 10:39:46 am
How does the reaction of the alkenes with the halogens differ from the reaction of the alkanes with the halogens?in alkanes+halogen, UV light should be present and u get mono-halogenoalkane and hydrogen halide ( or another longer alkane, if u study in DETAIL!) as byproduct, it is free-radical addition reaction
but in alkenes+halogen , u get di-halogenoalkane with no by product, it is neucliophilic addition reaction
SIMPLE
Post by: Vampire-Love4ever on April 14, 2011, 05:17:55 pm
Anyone having the answers to the EXAMZONE part of the questions in this textbook?
http://www.amazon.co.uk/Edexcel-Level-Science-Chemistry-Students/dp/1408206056/ref=pd_sim_b_7
Please!!! I hope someone does!!!
Post by: NidZ- Hero on April 16, 2011, 08:15:31 pm
?
Post by: NotAbod on April 16, 2011, 08:46:07 pm
Post by: EMO123 on April 17, 2011, 09:20:19 am
K(s) + O2 ? KO2(s) how does this reaction happen i mean wat r de steps2K(s)+O2-->2KO(s)
?
Post by: elemis on April 17, 2011, 09:36:06 am
2K(s)+O2-->2KO(s)
Your equation is incorrect.
@Nidzz Potassium, being an alkali metal, is very reactive with the oxygen in the air.
Hence,
4K(s)+O2(g)-->2K2O(s)
Post by: EMO123 on April 17, 2011, 12:49:20 pm
Your equation is incorrect.thanx ari
@Nidzz Potassium, being an alkali metal, is very reactive with the oxygen in the air.
Hence,
4K(s)+O2(g)-->2K2O(s)
Post by: red_911 on April 19, 2011, 06:03:43 pm
Post by: Amelia on April 19, 2011, 06:30:52 pm
water has which types of intermolecular forces ?? n which has higher boiling point HF or h2O ? explain with reason plzz ???
Please refrain from double posting. Your question has been answered in the CIE chemistry thread.
Post by: red_911 on April 19, 2011, 06:46:09 pm
it doesnt come under double posting in purpose. since i have a chemistry test tomorrow i wanted the answer urgently but no one was giving it here so posted it on the other page.
Please refrain from double posting. You question has been answered in the CIE chemistry thread.
Post by: ~ Miss Relina ~ on April 19, 2011, 07:52:45 pm
1. draw the double bond in terms of orbital overlap
2.why the strongest intermolecular forces in hydrogen halides in liquid form like HCl is van der waals npt permanenet dipole-dipole
i thought of this because HCl is dipolar or does the liqiud means something else
3.why the config... of copper atomis 1s*2 2s*2 2p*6 3s*2 3p*6 3d*10 4s*1
istead of 1s*2 2s*2 2p*6 3s*2 3p*6 3d*9 4s*2
Post by: The Golden Girl =D on April 20, 2011, 01:46:24 pm
my doubts :
1. draw the double bond in terms of orbital overlap
2.why the strongest intermolecular forces in hydrogen halides in liquid form like HCl is van der waals npt permanenet dipole-dipole
i thought of this because HCl is dipolar or does the liqiud means something else
3.why the config... of copper atomis 1s*2 2s*2 2p*6 3s*2 3p*6 3d*10 4s*1
istead of 1s*2 2s*2 2p*6 3s*2 3p*6 3d*9 4s*2
3. Because it is more stable in this case to have 10 electrons in the d-sub shell and only one electron in the 4s . not sure though but it's mainly cuz it's more stable.
Post by: elemis on April 20, 2011, 02:40:33 pm
it doesnt come under double posting in purpose. since i have a chemistry test tomorrow i wanted the answer urgently but no one was giving it here so posted it on the other page.
I dont care. Do not double post again.
Post by: Malak on April 20, 2011, 05:43:48 pm
Can anyone help me with the applications of nano-tubes?
I just need some brief uses of it.
Thx
Post by: The Golden Girl =D on April 20, 2011, 06:14:49 pm
water has which types of intermolecular forces ?? n which has higher boiling point HF or h2O ? explain with reason plzz ???
1.Hydrogen bonding since the O and H are bonded directly to each other.
2.the one with stronger bonding for sure but which one is it I'm not sure.
Post by: Amelia on April 20, 2011, 06:40:06 pm
Hey
Can anyone help me with the applications of nano-tubes?
I just need some brief uses of it.
Thx
Here (http://www.understandingnano.com/nanotubes-carbon.html)
Hope it helps. ;)
Post by: Malak on April 20, 2011, 10:03:59 pm
I am confused about something related to Dispersion forces and permanent dipoles..In the chemistry guide by NAS and even on a website for chemistry i have read that Permanent dipoles are weaker than dispersion forces.
The order is given as : Hydrogen bonding > dispersion (london forces) > permanent-dipole
But it other books the same order is given differently...It says that permanent dipoles have greater strength than dispersion forces..
I am not sure how I should treat it for Edexel exams??
Can anyone help with it??
Post by: Assi1993 on April 20, 2011, 11:30:29 pm
this is a question from january 2011 chem unit 5!
2 Which of these four amino acids could NOTTT rotate the plane of plane-polarised light?
A H2NCH(CH3)COOH
B H2NCH(CH2COOH)COOH
C H2NCH2COOH
D H2NCH(CH2SH)COOH
answer is C
I know that chiral carbon causes the rotation
but im confused about how do we know that which 1 has chiral centre and which doesnt :(
waiting for reply!-_-
Post by: HUSH1994 on April 21, 2011, 05:20:31 pm
Post by: EMO123 on April 21, 2011, 05:45:31 pm
hello all!
this is a question from january 2011 chem unit 5!
2 Which of these four amino acids could NOTTT rotate the plane of plane-polarised light?
A H2NCH(CH3)COOH
B H2NCH(CH2COOH)COOH
C H2NCH2COOH
D H2NCH(CH2SH)COOH
answer is C
I know that chiral carbon causes the rotation
but im confused about how do we know that which 1 has chiral centre and which doesnt :(
waiting for reply!-_-
ya it is C
draw all the structures
so which structure as both pie and sigma bong does not rotate
Post by: Assi1993 on April 21, 2011, 09:14:22 pm
Post by: Mike Benn on April 22, 2011, 03:43:06 pm
Post by: EMO123 on April 22, 2011, 04:13:09 pm
hey there....plz can anyone tell me what's the definition for Effective Nuclear Charge...( it should be exact pls . as me got my Unit 2 Exam this May )there are three answers i got it think and see which one would you prefer to understand.
1st answer-Effective nuclear charge is the portion of the nuclear charge that is experienced by the highest energy level electrons.
2nd answer-ENC is the charge felt by the valence electrons after you have found the number of shielding electrons that surround the nucleus.
3rd answer-Also known as the kernel charge, ENC is the net positive charge experienced by an electron in a multi-electron atom.
Post by: Mike Benn on April 22, 2011, 04:18:05 pm
Post by: EMO123 on April 22, 2011, 04:19:47 pm
Thankxx Dude..all 3 are worth memorising..:Pit's k anytime
Post by: Aadeez || Zafar on April 24, 2011, 06:15:54 am
hello all!chiral cntres are the carbon atom attached to four different atom/groups
this is a question from january 2011 chem unit 5!
2 Which of these four amino acids could NOTTT rotate the plane of plane-polarised light?
A H2NCH(CH3)COOH
B H2NCH(CH2COOH)COOH
C H2NCH2COOH
D H2NCH(CH2SH)COOH
answer is C
I know that chiral carbon causes the rotation
but im confused about how do we know that which 1 has chiral centre and which doesnt :(
waiting for reply!-_-
see this for more help
http://www.khanacademy.org/v/introduction-to-chirality?p=Organic%20Chemistry
http://www.khanacademy.org/v/chiral-examples-1?p=Organic%20Chemistry
http://www.khanacademy.org/v/chiral-examples-2?p=Organic%20Chemistry
Post by: EMO123 on April 24, 2011, 06:19:41 am
chiral cntres are the carbon atom attached to four different atom/groupsgot good videos bhiku Mr. Must :)
see this for more help
http://www.khanacademy.org/v/introduction-to-chirality?p=Organic%20Chemistry
http://www.khanacademy.org/v/chiral-examples-1?p=Organic%20Chemistry
http://www.khanacademy.org/v/chiral-examples-2?p=Organic%20Chemistry
Post by: Assi1993 on April 24, 2011, 02:30:32 pm
chiral cntres are the carbon atom attached to four different atom/groups
see this for more help
http://www.khanacademy.org/v/introduction-to-chirality?p=Organic%20Chemistry
http://www.khanacademy.org/v/chiral-examples-1?p=Organic%20Chemistry
http://www.khanacademy.org/v/chiral-examples-2?p=Organic%20Chemistry
thankYou so much!!+ rep:) God bless
Post by: Aadeez || Zafar on April 24, 2011, 05:15:30 pm
thankYou so much!!+ rep:) God blessthanks man got this aftr long time
Post by: Mike Benn on April 25, 2011, 10:52:07 am
Much Appreciated if someone sends it ..
Post by: red_911 on April 25, 2011, 03:04:56 pm
n if 2 bond n 2 lone pairs ?
Post by: Amelia on April 25, 2011, 04:09:53 pm
if there are 2 bond pairs n one lone pair what is the angle ?
You mean, three bond pairs and one lone pair...? It's 107.3°.
Quote
n if 2 bond n 2 lone pairs ?
104.4°
You will find a list of molecules, their shapes and angles Here (http://www.chem.ufl.edu/~myers/chm2045/shapes.htm)
Post by: red_911 on April 25, 2011, 05:14:28 pm
You mean, three bond pairs and one lone pair...? It's 107.3°.
104.4°
You will find a list of molecules, their shapes and angles Here (http://www.chem.ufl.edu/~myers/chm2045/shapes.htm)
thnkuu ameliaa :D :D
Post by: red_911 on April 25, 2011, 09:32:03 pm
Post by: Malak on April 26, 2011, 12:27:33 pm
when we talk of alcohols eg ethanol we say that it has london forces and hydrogen bonds but why not permanent di-pole forces as oxygen attached to carbon is more electronegative ?
Well..alcohols do have permanent dipole-dipole interactions other than hydrogen bonding and london forces...but i guess london forces are more significant thats why dipole-dipole isnt mentioned..
Someone else might answer better sorry
Post by: ~ Miss Relina ~ on April 26, 2011, 12:51:03 pm
my doubts :
1. draw the double bond in terms of orbital overlap
2.why the strongest intermolecular forces in hydrogen halides in liquid form like HCl is van der waals npt permanenet dipole-dipole
i thought of this because HCl is dipolar or does the liqiud means something else
plz guys answer me exams are near
Post by: Malak on April 26, 2011, 01:25:39 pm
Can anyone explain why?
I know we dont use sulfuric acid as it will oxidise the iodide or bromide ions but what about the Metal halide?
Thx
Post by: elemis on April 26, 2011, 03:26:40 pm
Carry out the preparation of an halogenoalkane from an alcohol and explain why a metal halide and concentrated sulphuric acid should not be used when making a bromoalkane or an iodoalkane
Can anyone explain why?
I know we dont use sulfuric acid as it will oxidise the iodide or bromide ions but what about the Metal halide?
Thx
Lets say you want to make 1-Chloroethane
You would react NaCl and H2SO4 to get NaHSO4 and HCl fumes. The HCl reacts with ethene to form the deisred product.
Now if you were to repeat the process using NaI and H2SO4 would you get a HI ?? No, you wouldnt. The primary product would be Iodine vapour and not HI.
Hence, the H2SO4 is a very very strong oxidising agent that oxidises the metal halide to its halide molecule.
Where is this question from ?
Post by: red_911 on April 26, 2011, 03:40:37 pm
Well..alcohols do have permanent dipole-dipole interactions other than hydrogen bonding and london forces...but i guess london forces are more significant thats why dipole-dipole isnt mentioned..
Someone else might answer better sorry
thanks for ur answer ;D
Post by: Malak on April 26, 2011, 03:52:27 pm
Lets say you want to make 1-Chloroethane
You would react NaCl and H2SO4 to get NaHSO4 and HCl fumes. The HCl reacts with ethene to form the deisred product.
Now if you were to repeat the process using NaI and H2SO4 would you get a HI ?? No, you wouldnt. The primary product would be Iodine vapour and not HI.
Hence, the H2SO4 is a very very strong oxidising agent that oxidises the metal halide to its halide molecule.
Where is this question from ?
Thx for your reply..
And this is not a question, its a point from the specification :)
Post by: ~ Miss Relina ~ on April 26, 2011, 11:25:21 pm
Post by: elemis on April 27, 2011, 05:09:50 am
plz need an answer soon
Hint : the longest carbon chain contains 5 carbons.
Post by: Aadeez || Zafar on April 27, 2011, 01:50:03 pm
plz need an answer soon
Post by: EMO123 on April 27, 2011, 03:33:51 pm
Post by: ~ Miss Relina ~ on April 27, 2011, 08:26:25 pm
Hint : the longest carbon chain contains 5 carbons.Thanks
Post by: ~ Miss Relina ~ on April 27, 2011, 08:28:04 pm
Thanks does this rule applies for all namings of such things
plz if u can help me with the rules of naming organic structures post anythigappreciating any effort
Post by: The Golden Girl =D on April 28, 2011, 02:04:26 pm
Thanks does this rule applies for all namings of such things
plz if u can help me with the rules of naming organic structures post anythigappreciating any effort
Indeed it does.
Here:
the last part here :
http://intro.chem.okstate.edu/1014/Lecture/Organic.html
http://www.chymist.com/organic%20nomeclature.pdf
I hope I helped :)
Post by: Aadeez || Zafar on April 28, 2011, 02:08:54 pm
Thanks does this rule applies for all namings of such thingssee this
plz if u can help me with the rules of naming organic structures post anythigappreciating any effort
http://www.khanacademy.org/v/naming-alkanes-with-alkyl-groups?p=Organic%20Chemistry
and some few video of example see the list of videos at
http://www.khanacademy.org/#organic-chemistry
are very helpful
Post by: ~ Miss Relina ~ on April 28, 2011, 11:30:56 pm
Indeed it does.yes u 've done Thanks
Here:
the last part here :
http://intro.chem.okstate.edu/1014/Lecture/Organic.html
http://www.chymist.com/organic%20nomeclature.pdf
I hope I helped :)
Post by: ~ Miss Relina ~ on April 28, 2011, 11:31:35 pm
see thisThanks alot
http://www.khanacademy.org/v/naming-alkanes-with-alkyl-groups?p=Organic%20Chemistry
and some few video of example see the list of videos at
http://www.khanacademy.org/#organic-chemistry
are very helpful
Post by: ~ Miss Relina ~ on April 29, 2011, 11:59:51 am
Post by: red_911 on April 29, 2011, 12:26:31 pm
i need help with the shapes of the organic compound like e.g i dodnt know how to differentiate whether a compound to be trigona; pyramidal or trigonal pyramidal or trigonal planar or bent linear ??? plz any help with that issue
i think this will help you
http://www.youtube.com/watch?v=i3FCHVlSZc4
Post by: red_911 on April 29, 2011, 12:29:09 pm
A 35.5
B 36
C 71
D 72
the ans is D .. but can anyone explain me how ?m ??? ??? :-\
Post by: ~ Miss Relina ~ on April 29, 2011, 02:13:53 pm
Question : chlorine has two isotopes with the relative isotopic mass 35 and 37. Four m/z values are given below, Which will occur in a mass spectrum of chlorine gas, CL2 from an ion with a single positive charge ?because cl2 is diatomic so u would have a combination of 1-35+35=70 2-35+37=72 3-37+37=74
A 35.5
B 36
C 71
D 72
the ans is D .. but can anyone explain me how ?m ??? ??? :-\
and for D it equals 35+37 for the cl2+ ion hope u understood
Post by: ~ Miss Relina ~ on April 29, 2011, 02:29:34 pm
a;so on Jan OLD EXAMS question 2 (d) plz
Post by: NidZ- Hero on April 29, 2011, 05:23:28 pm
Post by: Aadeez || Zafar on April 29, 2011, 07:13:08 pm
Post by: ~ Miss Relina ~ on April 29, 2011, 07:28:28 pm
see thisis this required inas-level syllabus :-\
Post by: NidZ- Hero on April 29, 2011, 08:55:00 pm
:-\
Post by: ~ Miss Relina ~ on April 29, 2011, 09:52:41 pm
any help appreciated
http://www.xtremepapers.me/Edexcel/Advanced%20Level/Chemistry/2009%20Jan/6CH01-01-que-20090109.pdf
why ch3coch3 best solvent for alcohol(cyclohexanol) than water???
need answers for these sssssssssssooooon :-[ :(
Post by: EMO123 on April 30, 2011, 03:31:20 am
if You have got data booklet see in it
Post by: EMO123 on April 30, 2011, 04:45:53 am
isomers are representation of molecular formula in different structural form
C5 H12
can have 2 isomers and a straight chain
1. 2,methyl butane
2 2 2 dimethyl propane
3. straight chain
you can draw structures to understand.
answer is B
Post by: elemis on April 30, 2011, 05:33:31 am
Ok how do you name this ?
:-\
Is it the first one ?
Post by: NidZ- Hero on April 30, 2011, 05:39:35 am
Is it the first one ?no all de three are de name for the same compound.. but i wonder how do you get dat especailly de second one
Post by: EMO123 on April 30, 2011, 08:44:40 am
Post by: The Golden Girl =D on April 30, 2011, 09:21:46 am
please guys in this exam question 6 and 14 explain why u chose each and tell me the difference
any help appreciated
http://www.xtremepapers.me/Edexcel/Advanced%20Level/Chemistry/2009%20Jan/6CH01-01-que-20090109.pdf
why ch3coch3 best solvent for alcohol(cyclohexanol) than water???
need answers for these sssssssssssooooon :-[ :(
ethanol is an inert solvent it won't interfere in the reaction it will only allow them to mix that's it, where as water acts as a neucleophile and it converts cyclohexanol into cyclohexene.
Correct me if I'm wrong.
Post by: ~ Miss Relina ~ on April 30, 2011, 02:37:13 pm
ethanol is an inert solvent it won't interfere in the reaction it will only allow them to mix that's it, where as water acts as a neucleophile and it converts cyclohexanol into cyclohexene.
Correct me if I'm wrong.
well i'm not sure but does alcohol gives alkene with water ???
well i think alcohol when dehyrated and water removed it gives alkene ???
Post by: Aadeez || Zafar on April 30, 2011, 04:36:57 pm
well i'm not sure but does alcohol gives alkene with water ???
well i think alcohol when dehyrated and water removed it gives alkene ???
ALCOHOL ----> ALKENES
condition : - hot pumice (Porous ceramic surface) and Al2O3
Post by: NidZ- Hero on May 01, 2011, 05:36:50 am
Post by: elemis on May 01, 2011, 05:49:12 am
Hey wats de difference between an ion n a radical ? is radical just a normal atom
An ion is a charged species that has either lost or gained electron(s) such that it either has a deficiency or excess of electrons.
A radical is just an ordinary atom/group of atoms with an unpaired electron.
Post by: NidZ- Hero on May 01, 2011, 06:45:47 am
but hey my doubts r never ending
So yeah in this propagation step in clorination of methane
Cl*+Ch4----->CH3Cl+H*
Cl*+Ch4----->HCL+Ch3*
So why is de second reaction more likely
Post by: elemis on May 01, 2011, 06:51:37 am
thanx Ari Ben
but hey my doubts r never ending
So yeah in this propagation step in clorination of methane
Cl*+Ch4----->CH3Cl+H*
Cl*+Ch4----->HCL+Ch3*
So why is de second reaction more likely
The first reaction is slightly endothermic compared to the second one which is exotehrmic. Exothermic reactions result in more stable product hence the second one is more likely.
Post by: NidZ- Hero on May 01, 2011, 06:56:50 am
The first reaction is slightly endothermic compared to the second one which is exotehrmic. Exothermic reactions result in more stable product hence the second one is more likely.a stupid question isint dat exothermic reaction have extra energy so de are unstable in order to gt rid of de energy the react......
Post by: elemis on May 01, 2011, 11:52:01 am
a stupid question isint dat exothermic reaction have extra energy so de are unstable in order to gt rid of de energy the react......
I'm not sure I follow. In an exothermic reaction the PRODUCTS are at a lower energy level and hence more stable then the REACTANTS.
Post by: NidZ- Hero on May 01, 2011, 07:39:34 pm
Is it Purple -----> colourless
OR
purple solution first becomes dark green and then produces a dark brown precipitate.
in my boook its de first one
Post by: Deadly_king on May 01, 2011, 07:42:30 pm
whats the colour change when you add cold potassium permanganate in an alkaline solutionn\ to alkene ?
Is it Purple -----> colourless
OR
purple solution first becomes dark green and then produces a dark brown precipitate.
in my boook its de first one
It's the first one itself ;)
When alkaline KMnO4 is added to an alkene, it causes oxidation of the alkene while itslef gets reduced.
This is why the colour change from purple to colourless represnts reduction of KMnO4.
i wonder where did you get dark green and dark brown ppt :P
Post by: NidZ- Hero on May 02, 2011, 01:03:54 am
Post by: elemis on May 02, 2011, 08:45:20 am
Can Some one help me wid 2009 Unit 1 21 C (iv)
Could you post a link ?
Post by: NidZ- Hero on May 02, 2011, 11:02:29 am
Could you post a link ?http://www.freeexampapers.com/past_papers.php?l=Past_Papers%2FA+Level%2FChemistry%2FEdexcel%2F2009+Jun/
Post by: NidZ- Hero on May 02, 2011, 11:15:18 am
and do we have these kind of isomers to name
Post by: elemis on May 02, 2011, 11:45:29 am
http://www.freeexampapers.com/past_papers.php?l=Past_Papers%2FA+Level%2FChemistry%2FEdexcel%2F2009+Jun/
Doing it now.
Post by: elemis on May 02, 2011, 11:51:52 am
Thus, the hydrogen will add across each double bond.
Construct an equation :
C10H16 + H2 ------> X
NOTE : X is the product that we are trying to determine the structural formula of.
1.36 grams of the Mycrene reacted. 1.36/136 = 0.01 moles
0.72 dm3 of Hydrogen reacted. 0.72/24 = 0.03 moles
Notice that the ration of Mycrene to Hydrogen is 1:3
Therefore for every one mole of Mycrene 3 moles of hydrogen MOLECULES are required.
Balancing the equation :
C10H16 + 3H2 ------> X
Now you have proven that 6 hydrogen ATOMS are added just draw the formula !
Post by: Darkstar3000 on May 02, 2011, 11:54:49 am
a) What was the pH when 24.95 cm^3 of 1.00 mol dm^-3 NaOh (aq) had been added to 25 cm^3 of 1.00 mol dm^-3 HCL(aq) ? ANS : 3
How do I calculate this ? I tried calculation and what I did was -log 2 and subtracted the answer from 14 but it makes no difference. Can you please explain this with as much detail as possible because I'm a bit shakey on this
Thank you
Post by: NidZ- Hero on May 02, 2011, 12:26:08 pm
Firstly, you have to understand we are basically reacting an alkene with Hydrogen to produce a product that has NO double bonds.Thanks alot buddy but i was askin How to draw its kinda a different
Thus, the hydrogen will add across each double bond.
Construct an equation :
C10H16 + H2 ------> X
NOTE : X is the product that we are trying to determine the structural formula of.
1.36 grams of the Mycrene reacted. 1.36/136 = 0.01 moles
0.72 dm3 of Hydrogen reacted. 0.72/24 = 0.03 moles
Notice that the ration of Mycrene to Hydrogen is 1:3
Therefore for every one mole of Mycrene 3 moles of hydrogen MOLECULES are required.
Balancing the equation :
C10H16 + 3H2 ------> X
Now you have proven that 6 hydrogen ATOMS are added just draw the formula !
Post by: elemis on May 02, 2011, 02:54:16 pm
Thanks alot buddy but i was askin How to draw its kinda a different
Just add hydrogens across each double bond.... what's so difficult ?
Post by: ~ Miss Relina ~ on May 02, 2011, 03:19:14 pm
Thanks alot buddy but i was askin How to draw its kinda a differenthere
Post by: ~ Miss Relina ~ on May 02, 2011, 09:30:19 pm
2.how to prepare a saturated solution accurately ???
3.explain the mean bond enthalpy and distinguissh between ti and the bond enthalpy ???
Thanks in advance
Post by: Vampire-Love4ever on May 02, 2011, 11:34:43 pm
The answer which I wrote is from the marking scheme and its for two marks but only 1 point is given-which I dont understand. :/
Post by: Vampire-Love4ever on May 02, 2011, 11:38:52 pm
Post by: Vampire-Love4ever on May 02, 2011, 11:49:11 pm
In the marking scheme, they havent mentioned anything about the flask being sealed which will lead to pressure build up.
So, if I mention this point in the exam- will it be wrong?
This from June 2011 Unit6b Q4biii
Post by: NidZ- Hero on May 03, 2011, 05:03:54 am
the image attached is used to reflux organic compound and we must find two mistakes in the diagram.Alrite i just Know that water inlet arrangement is wrong water enter from down and leave from top of condenser
In the marking scheme, they havent mentioned anything about the flask being sealed which will lead to pressure build up.
So, if I mention this point in the exam- will it be wrong?
This from June 2011 Unit6b Q4biii
Post by: NidZ- Hero on May 03, 2011, 06:12:57 am
Post by: SkyPilotage on May 03, 2011, 10:14:40 am
write the formula of compound iron(iii) nitrate(v) ?Its Fe(NO3)3 --->also called as ferric nitrate.
The 3 for the iron and the 5 is for the nitrogen in the nitrate...
Post by: elemis on May 03, 2011, 10:27:26 am
write the formula of compound iron(iii) nitrate(v) ?
The valency of Nitrate is not 5.
Post by: SkyPilotage on May 03, 2011, 10:29:05 am
The valency of Nitrate is not 5.Acutally the 5 is for the Nitrogen so its NO3 where N is +5 and O is -6 so its NO3-
There is also nitrate (iii) where N is +3 and O is -4 so its NO2-..
Post by: elemis on May 03, 2011, 10:39:12 am
Acutally the 5 is for the Nitrogen so its NO3 where N is +5 and O is -6 so its NO3-
There is also nitrate (iii) where N is +3 and O is -4 so its NO2-..
Yeah, I know that, but by putting the 5 in brackets right next to the nitrate Nidzzz is implying she thinks the valency of the nitrate ion is -5.
Post by: red_911 on May 03, 2011, 11:21:48 am
unit 2 January 2010 question 16.
in the mark scheme they have told the answer for magnesium nitrate decomposing at higher temperature than calcium nitrate ??? ???
correct me if i am wrong :-X :-X
Post by: Darkstar3000 on May 03, 2011, 12:54:37 pm
a) What was the pH when 24.95 cm^3 of 1.00 mol dm^-3 NaOh (aq) had been added to 25 cm^3 of 1.00 mol dm^-3 HCL(aq) ? ANS : 3
How do I calculate this ? I tried calculation and what I did was -log 2 and subtracted the answer from 14 but it makes no difference. Can you please explain this with as much detail as possible because I'm a bit shakey on this
Thank you
Post by: **RoRo** on May 03, 2011, 01:23:33 pm
1. 50cm3 if a solution of citric acid, Mr=192, containing 19.2 g dm-3 reacted with 50cm3 of a solution of sodium hydroxide containing 12 g dm-3. Citric acid can be represented by the formula HxA, where x represents the number of hydrogen atoms in a molecule. Use the data above to calculate the number of moles of sodium hydroxide that react with one mole of citric acid and hence find the find the value of x.
I found the number of moles to be 3 moles, but how do you know that x=3?
2. When 20cm3 of of ammonia gas is passed over a catalyst with excess oxygen, 20cm3 of nitrogen monoxide (NO) and 30cm3 of water vapour are produced. Use this data to write out the equation for the reaction.
Honestly, I did it by just simple balancing - how do you use the data to determine the equation?
The answer is 4NH3 + 5O2 -----> 4NO + 6H2O
3. When 8.4g of sodium hydrogen carbonate are heated 5.30g of solid residue and 1200 cm3 of carbon dioxide are produced and 0.900g of water are evolved. Show that this data is consistent with the following equation.
2NaHCO3 -----> Na2CO3 + CO2 + H2O
How do you prove that?
4. Sulphur dioxide can be removed from the waste gases of a power station by passing it through a slurry of calcium hydroxide. The equation for this reaction is:
SO2(g) + Ca(OH)2(aq) -----> CaSO3(aq) + H2O(l)
What mass of calcium hydroxide would be needed to deal with 1000dm3 of sulphur dioxide?
I'm getting the answer as 3087.5g, but the answer is supposed to be 324.3 [I'm not sure though, because I copied it down from someone] so can someone please confirm?
5. Chlorine reacts with sodium hydroxide as follows:
Cl2(g) + 6NaOH(aq) -----> 5NaCl(aq) + NaClO3(aq) + 3H2O(l)
What mass of sodium chloride and what mass of sodium(V)chlorate would be produced from 240 cm3 of chlorine gas?
The mass of NaClO3 is 1.065, but for the mass of NaCl, I'm getting it as 2.925g when also in the paper, I copied it as 2.94g, so which one is right and if it's 2.94, how do you arrive to such an answer?
6. When nitrogen reacts with hydrogen in the Haber process only 17% of the nitrogen is converted to ammonia. What volume of nitrogen and what volume of hydrogen would be needed to produce one tonne of ammonia? (1 tonne = 1 x 106 g)
The answer is supposed to be 4.15x106 dm3 of N2 and 12.5x106 dm3 of H2 & I don't know how to arrive to either of the answers!
7. Nitric acid is produced by the following series of reactions:
4NH3 + 5O2 ----> 4NO + 3H2O
4NO + O2 ----> 4NO2
4NO2 + O2 + 2H2O ----> 4HNO3
What mass of nitric acid would be produced from 17 tonnes of ammonia and what volume of oxygen would be needed in the reaction?
I got the mass right, it's 63 tonnes, but for the volume I'm getting it as 3.05x107dm3 when it's supposed to be 4.8x107dm3!
8. 25cm3 of a solution of an acid HxA containing 0.1 mol dm-3 of the acid in each 1000cm3 of solution reacts with 75cm3 of a solution of 0.1 mol dm-3 NaOH. What is the value of x?
The answer is x=3, I solved this question till I reached to the part where 1 mole of HxA reacts with 3 moles of NaOH, but I don't know how do you decide that x=3?
Phewww, that's it! I'm very sorry for the length of my post!
Post by: elemis on May 03, 2011, 04:02:34 pm
Write out the ionic equation :
XH+ + OH- ----> H2O
Since the formula of the acid is HxA this means it can dissociate and give X Hydrogen ions to neutralise the sodium hydroxide.
Hence, I wrote an in front of the H+
Next, calculate the no. of moles of Hyrdogen ions and Hydroxide ions.
Moles of hydrogen ions = moles of acid. Moles of hydroxide ions = moles of NaOH
You have to convert the grams/dm3 to mol/dm3 :
19.2/192 = 0.1 mol/dm3 <---- just divide by the molar mass
12/(23+17) = 0.3 mol/dm3
No. of moles = concentration (calculated above) *volume (in decimetre cube)
You should get 0.015 moles for OH- and 5*10^-3 moles for H+
Insert into the equation and determine the stochiometric ratio :
0.015/(5*10^-3) = 3/1
What this means is that 3 moles of Hydroxide ions are neutralised by ONE mole of the acid.
So the acid must dissociate to give 3 moles of HYDROGEN ions.
Hence, x = 3
Question 2
Write the unbalanced equation :
NH3 + O2 ----> NO + H2O
Calculate the no. of moles of each chemical :
20/24000 = 1/1200 moles of Ammonia and Nitrogen Monoxide
30/24000 = 1/800 moles of Water.
Determine the ratio:
moles of Ammonia : moles of Water = 2:3
Insert this into the equation :
2NH3 + O2 ----> NO + 3H2O
moles of ammonia : moles of NO = 1:1 = 2 : 2
Insert :
2NH3 + O2 ----> 2NO + 3H2O
Balance for oxygen :
2NH3 +
Post by: NidZ- Hero on May 03, 2011, 04:45:32 pm
Yeah, I know that, but by putting the 5 in brackets right next to the nitrate Nidzzz is implying she thinks the valency of the nitrate ion is -5.YEAhj i Gt the Point De valency of Nitrogen is -5 Not nitrate
Post by: SkyPilotage on May 03, 2011, 04:56:21 pm
YEAhj i Gt the Point De valency of Nitrogen is -5 Not nitrate+5 :D
Post by: NidZ- Hero on May 05, 2011, 05:45:26 am
:o
Post by: elemis on May 05, 2011, 06:39:05 am
How is it possible for chlorine to The maximum oxidation state of +7?
:o
Reacting hot NaOH and Chlroine gas will cause disproportionation with the Cl attaining an oxidation state of +7 and -1 simultaneously (though in different products).
Post by: **RoRo** on May 05, 2011, 08:53:32 am
Question 1
Write out the ionic equation :
XH+ + OH- ----> H2O
Since the formula of the acid is HxA this means it can dissociate and give X Hydrogen ions to neutralise the sodium hydroxide.
Hence, I wrote an in front of the H+
Next, calculate the no. of moles of Hyrdogen ions and Hydroxide ions.
Moles of hydrogen ions = moles of acid. Moles of hydroxide ions = moles of NaOH
You have to convert the grams/dm3 to mol/dm3 :
19.2/192 = 0.1 mol/dm3 <---- just divide by the molar mass
12/(23+17) = 0.3 mol/dm3
No. of moles = concentration (calculated above) *volume (in decimetre cube)
You should get 0.015 moles for OH- and 5*10^-3 moles for H+
Insert into the equation and determine the stochiometric ratio :
0.015/(5*10^-3) = 3/1
What this means is that 3 moles of Hydroxide ions are neutralised by ONE mole of the acid.
So the acid must dissociate to give 3 moles of HYDROGEN ions.
Hence, x = 3
Question 2
Write the unbalanced equation :
NH3 + O2 ----> NO + H2O
Calculate the no. of moles of each chemical :
20/24000 = 1/1200 moles of Ammonia and Nitrogen Monoxide
30/24000 = 1/800 moles of Water.
Determine the ratio:
moles of Ammonia : moles of Water = 2:3
Insert this into the equation :
2NH3 + O2 ----> NO + 3H2O
moles of ammonia : moles of NO = 1:1 = 2 : 2
Insert :
2NH3 + O2 ----> 2NO + 3H2O
Balance for oxygen :
2NH3 +O2 ----> 2NO + 3H2O
Thank you very much for your help, I really appreciate it! :)
Post by: **RoRo** on May 05, 2011, 08:55:50 am
What's the explanation for the fact that the more branched the molecules in the fractions of crude oil are, the more useful the fuel is? Is it the fact that they have a lower boiling point because they'd have less intermolecular forces between the molecules as a result of the smaller surface area?
Post by: Master_Key on May 05, 2011, 12:23:04 pm
Another question guys, added to my previous set of questions! :P
What's the explanation for the fact that the more branched the molecules in the fractions of crude oil are, the more useful the fuel is? Is it the fact that they have a lower boiling point because they'd have less intermolecular forces between the molecules as a result of the smaller surface area?
I think shorter chain fuels are more useful. The branch can then be explained that when cracking these branched chain alkanes/alkenes they give useful product. The latter is correct. Your concept of intermolecular force is correct.
Gasoline(4-8 Carbon atoms).
Post by: **RoRo** on May 05, 2011, 12:41:26 pm
I think shorter chain fuels are more useful. The branch can then be explained that when cracking these branched chain alkanes/alkenes they give useful product. The latter is correct. Your concept of intermolecular force is correct.
Gasoline(4-8 Carbon atoms).
I'm sorry, I didn't get your point!
Shorter chains are more useful, as in they're more in demand, yes, I agree - that wasn't related to my question though!
"The branch can then be explained that when cracking these branched chain alkanes/alkenes they give useful product." - What do you mean by this sentence?
The question compares more the difference between a straight-chain molecule and a branched molecule in terms of their efficiency as fuels.
Thanks for trying though, if you can help elaborate any further on your point, that would be great! xD
Post by: Master_Key on May 05, 2011, 12:53:48 pm
I'm sorry, I didn't get your point!
Shorter chains are more useful, as in they're more in demand, yes, I agree - that wasn't related to my question though!
"The branch can then be explained that when cracking these branched chain alkanes/alkenes they give useful product." - What do you mean by this sentence?
The question compares more the difference between a straight-chain molecule and a branched molecule in terms of their efficiency as fuels.
Thanks for trying though, if you can help elaborate any further on your point, that would be great! xD
Okay then dont consider length of fuels. Branched chain fuels have lower intermolecular forces as you said and if used directly then they are liquids or gases. Enthalpy change of combustion will differ. When they are cracked (heating over hot pumice(Al2O3)) to produce shorter chain alkanes then too they are more efficient and produce suitable alkanes.
Post by: EMO123 on May 05, 2011, 04:09:45 pm
Okay then dont consider length of fuels. Branched chain fuels have lower intermolecular forces as you said and if used directly then they are liquids or gases. Enthalpy change of combustion will differ. When they are cracked (heating over hot pumice(Al2O3)) to produce shorter chain alkanes then too they are more efficient and produce suitable alkanes.thanx man for me also it is damm worthy
Post by: ~ Miss Relina ~ on May 05, 2011, 05:48:16 pm
well 1.what is the benedict's solution used for ???hello there anyone
2.how to prepare a saturated solution accurately ???
3.explain the mean bond enthalpy and distinguissh between ti and the bond enthalpy ???
Thanks in advance
Post by: ~ Miss Relina ~ on May 05, 2011, 05:53:03 pm
the image attached is used to reflux organic compound and we must find two mistakes in the diagram.is it June 2011 ???
In the marking scheme, they havent mentioned anything about the flask being sealed which will lead to pressure build up.
So, if I mention this point in the exam- will it be wrong?
This from June 2011 Unit6b Q4biii
post the whole question plz
Post by: ~ Miss Relina ~ on May 05, 2011, 06:00:44 pm
the image attached is used to reflux organic compound and we must find two mistakes in the diagram.
In the marking scheme, they havent mentioned anything about the flask being sealed which will lead to pressure build up.
So, if I mention this point in the exam- will it be wrong?
This from June 2011 Unit6b Q4biii
well ithink it should not be sealed because its heating under reflux
Post by: Vampire-Love4ever on May 05, 2011, 10:37:27 pm
well ithink it should not be sealed because its heating under reflux
Thats what I thought too but the marking scheme doesnt mention it! :/
Post by: NidZ- Hero on May 06, 2011, 12:51:38 am
Thats what I thought too but the marking scheme doesnt mention it! :/R3ad this http://www.rod.beavon.clara.net/reflux.htm
Post by: NidZ- Hero on May 06, 2011, 01:30:12 am
Post by: elemis on May 06, 2011, 04:37:29 am
Can some tell me the obeservation of the reaction when halide reacts with conc H2SO4
Depends on the halide ion in the reagent. If its a chloride you would see white fumes of Hydrogen Chloride.
If its Bromide you would see the brown vapour of Bromine and fumes of HBr.
An Iodide would react to give the stinking smell of Hydrogen Sulphide and you would see the purple vapour of I2.
Post by: red_911 on May 06, 2011, 12:47:59 pm
Post by: EMO123 on May 06, 2011, 12:53:58 pm
when do we use starch as an indicator n what is sodium thiosulfate ? ??? ??? ???on adding Iodine to the starch it changes the color to black this shows starch is present in that
and what is sodium thiosulfate is given in the site bellow
http://en.wikipedia.org/wiki/Sodium_thiosulfate
Post by: **RoRo** on May 06, 2011, 03:00:15 pm
Quote
3. When 8.4g of sodium hydrogen carbonate are heated 5.30g of solid residue and 1200 cm3 of carbon dioxide are produced and 0.900g of water are evolved. Show that this data is consistent with the following equation.
2NaHCO3 -----> Na2CO3 + CO2 + H2O
How do you prove that?
4. Sulphur dioxide can be removed from the waste gases of a power station by passing it through a slurry of calcium hydroxide. The equation for this reaction is:
SO2(g) + Ca(OH)2(aq) -----> CaSO3(aq) + H2O(l)
What mass of calcium hydroxide would be needed to deal with 1000dm3 of sulphur dioxide?
I'm getting the answer as 3087.5g, but the answer is supposed to be 324.3 [I'm not sure though, because I copied it down from someone] so can someone please confirm?
5. Chlorine reacts with sodium hydroxide as follows:
Cl2(g) + 6NaOH(aq) -----> 5NaCl(aq) + NaClO3(aq) + 3H2O(l)
What mass of sodium chloride and what mass of sodium(V)chlorate would be produced from 240 cm3 of chlorine gas?
The mass of NaClO3 is 1.065, but for the mass of NaCl, I'm getting it as 2.925g when also in the paper, I copied it as 2.94g, so which one is right and if it's 2.94, how do you arrive to such an answer?
6. When nitrogen reacts with hydrogen in the Haber process only 17% of the nitrogen is converted to ammonia. What volume of nitrogen and what volume of hydrogen would be needed to produce one tonne of ammonia? (1 tonne = 1 x 106 g)
The answer is supposed to be 4.15x106 dm3 of N2 and 12.5x106 dm3 of H2 & I don't know how to arrive to either of the answers!
7. Nitric acid is produced by the following series of reactions:
4NH3 + 5O2 ----> 4NO + 3H2O
4NO + O2 ----> 4NO2
4NO2 + O2 + 2H2O ----> 4HNO3
What mass of nitric acid would be produced from 17 tonnes of ammonia and what volume of oxygen would be needed in the reaction?
I got the mass right, it's 63 tonnes, but for the volume I'm getting it as 3.05x107dm3 when it's supposed to be 4.8x107dm3!
8. 25cm3 of a solution of an acid HxA containing 0.1 mol dm-3 of the acid in each 1000cm3 of solution reacts with 75cm3 of a solution of 0.1 mol dm-3 NaOH. What is the value of x?
The answer is x=3, I solved this question till I reached to the part where 1 mole of HxA reacts with 3 moles of NaOH, but I don't know how do you decide that x=3?
& now another question:
When 4.0g of ammonium nitrate (NH4NO3) dissolves in 100cm3 of water, the temperature falls by 3.0oC. Calculate the enthalpy change per mole when NH4NO3 dissolves in water under these conditions,
First I find the amount of NH4NO3 used and that's 4/80=0.05 mol
Then I calculate the energy absorbed = m x c x T
Shouldn't m be 104 because it's 100cm3 of water = 100g and 4 g of NH4NO3 so 104g?
My textbook says it should be 100g, why so?
& then I know the rest of the procedure.
Thank you! :)
Post by: elemis on May 06, 2011, 03:26:51 pm
& now another question:
When 4.0g of ammonium nitrate (NH4NO3) dissolves in 100cm3 of water, the temperature falls by 3.0oC. Calculate the enthalpy change per mole when NH4NO3 dissolves in water under these conditions,
First I find the amount of NH4NO3 used and that's 4/80=0.05 mol
Then I calculate the energy absorbed = m x c x T
Shouldn't m be 104 because it's 100cm3 of water = 100g and 4 g of NH4NO3 so 104g?
My textbook says it should be 100g, why so?
& then I know the rest of the procedure.
Thank you! :)
You ignore the mass of Ammonium Nitrate since you are measure the temperature change of the water.... not the Ammonium Nitrate.
Post by: elemis on May 06, 2011, 03:41:47 pm
Calculate the no. of moles of each quantity as per the data. Check to see if they are consistent with the molar ratio of all the chemicals in the equation.
Question 4
Your answer seems to be correct.
Question 5
Your answer for the mass of NaCl is correct.
Question 6
N2 + 3 H2 ---> 2 NH3
(1*10^6)/(14+3) = 58823.5 moles of Ammonia.
In a reaction where ALL the Nitrogen reacts this would equate to a need for 29411.8 moles of Nitrogen.
BUT, only 17% of the Nitrogen we put in reacts. Therefore, 83% goes to waste.
We consider the 29411.8 moles of Nitrogen to represent the amount that REACTS i.e. the 17%.
Hence, 0.17*x = 29411.8
Solve for x and you will get the answer you have listed. Use the molar ratio to find the required volume of Hydrogen.
Question 7
I seem to be getting the same answer as you.
Question 8
The very first question was something along these lines. Apply yourself and think about it. If you cant figure it out I'll help.
Post by: **RoRo** on May 06, 2011, 04:55:31 pm
Question 6
N2 + 3 H2 ---> 2 NH3
(1*10^6)/(14+3) = 58823.5 moles of Ammonia.
In a reaction where ALL the Nitrogen reacts this would equate to a need for 29411.8 moles of Nitrogen.
BUT, only 17% of the Nitrogen we put in reacts. Therefore, 83% goes to waste.
We consider the 29411.8 moles of Nitrogen to represent the amount that REACTS i.e. the 17%.
Hence, 0.17*x = 29411.8
Solve for x and you will get the answer you have listed. Use the molar ratio to find the required volume of Hydrogen.
Well, when I solve for x, I get x = 173010.5882 which is the answer that I got earlier, but it's not the same as the answer given, thanks for that, I guess this answer is the right one then, I'll try to meet my teacher soon and confirm with her.
Question 8
The very first question was something along these lines. Apply yourself and think about it. If you cant figure it out I'll help.
I got that, thank you! :)
Just one more question here,
Quote
When 4.0g of ammonium nitrate (NH4NO3) dissolves in 100cm3 of water, the temperature falls by 3.0oC. Calculate the enthalpy change per mole when NH4NO3 dissolves in water under these conditions,
First I find the amount of NH4NO3 used and that's 4/80=0.05 mol
Then I calculate the energy absorbed = m x c x T
Shouldn't m be 104 because it's 100cm3 of water = 100g and 4 g of NH4NO3 so 104g?
My textbook says it should be 100g, why so?
& then I know the rest of the procedure.
Post by: ~ Miss Relina ~ on May 06, 2011, 08:34:56 pm
well 1.what is the benedict's solution used for ???
2.how to prepare a saturated solution accurately ???
3.explain the mean bond enthalpy and distinguissh between ti and the bond enthalpy ???
Thanks in advance
Post by: The Golden Girl =D on May 06, 2011, 08:39:29 pm
well 1.what is the benedict's solution used for ???
2.how to prepare a saturated solution accurately ???
3.explain the mean bond enthalpy and distinguissh between ti and the bond enthalpy ???
Thanks in advance
1.test for aldehyde and ketone ..... it gives a red ppt for aldehyde and no ppt for ketone :)
2. Add solute till no more dissolves.
3.don't remember unit 1 -.-
Post by: **RoRo** on May 06, 2011, 08:45:55 pm
Bond enthalpies are precise values for one kind of bond in different compounds. (e.g. for the C-Cl bond in CH3Cl).
Mean bond enthalpies are average values for one kind of bond in different compounds. (e.g. an average value for the C-Cl bond in all compounds)
Post by: ~ Miss Relina ~ on May 06, 2011, 09:45:48 pm
1.test for aldehyde and ketone ..... it gives a red ppt for aldehyde and no ppt for ketone :)Thanks
2. Add solute till no more dissolves.
3.don't remember unit 1 -.-
Post by: ~ Miss Relina ~ on May 06, 2011, 09:46:01 pm
Bond enthalpy of a particular bond is the energy required to break one mole of the bonds in a substance in the gaseous state.Thanks :)
Bond enthalpies are precise values for one kind of bond in different compounds. (e.g. for the C-Cl bond in CH3Cl).
Mean bond enthalpies are average values for one kind of bond in different compounds. (e.g. an average value for the C-Cl bond in all compounds)
Post by: **RoRo** on May 06, 2011, 11:25:30 pm
Thanks :)
You're welcome! :)
Post by: **RoRo** on May 06, 2011, 11:28:16 pm
Explain the following statements about oil refining in terms of intermolecular forces.
a) It is possible to separate the hydrocarbons in crude oil into fractions by distillation. [3 marks]
b) Cracking turns a mixture of liquids from crude oil into a mixture of gases. [2 marks]
c) Isomerisation turns straight chain alkanes into alkanes with lower boiling temperatures. [2 marks]
Thank you! :)
Post by: elemis on May 07, 2011, 05:58:54 am
Well, when I solve for x, I get x = 173010.5882 which is the answer that I got earlier, but it's not the same as the answer given, thanks for that, I guess this answer is the right one then, I'll try to meet my teacher soon and confirm with her.
I got that, thank you! :)
Just one more question here,
Yes, that is the no. of moles of the gas. Now convert to volume.
I've answered it on the previous page.
Post by: **RoRo** on May 07, 2011, 08:03:04 am
Yes, that is the no. of moles of the gas. Now convert to volume.
I've answered it on the previous page.
Ahaaa, I got it, thanks a lot and sorry for all the trouble! :)
Post by: elemis on May 07, 2011, 08:16:27 am
Another question:
Explain the following statements about oil refining in terms of intermolecular forces.
a) It is possible to separate the hydrocarbons in crude oil into fractions by distillation. [3 marks]
b) Cracking turns a mixture of liquids from crude oil into a mixture of gases. [2 marks]
c) Isomerisation turns straight chain alkanes into alkanes with lower boiling temperatures. [2 marks]
Thank you! :)
a) By fractional distillation - yes.
b) Not necessarily. Cracking a long chain alkane may just give you a long change alkene (which is likely to be liquid) and hydrogen, for example.
c) Branched hydrocarbons have weaker van der waals forces of attraction hence lower boiling points.
Post by: **RoRo** on May 07, 2011, 08:19:44 pm
a) By fractional distillation - yes.
b) Not necessarily. Cracking a long chain alkane may just give you a long change alkene (which is likely to be liquid) and hydrogen, for example.
c) Branched hydrocarbons have weaker van der waals forces of attraction hence lower boiling points.
mmm, what points should be mentioned for part a) to gain the 3 marks?
b) The question says explain the statement in terms of IMF, so how would you answer that?
&&&&
another question, do we need to study the procedure, the equations and the calculations method for the iodine-thiosulfate titrations like
-Finding the purity of potassium Iodate (V)
-Finding the % of Copper in Brass
-Finding the concentration of domestic bleach
Post by: Master_Key on May 08, 2011, 08:39:58 am
mmm, what points should be mentioned for part a) to gain the 3 marks?
b) The question says explain the statement in terms of IMF, so how would you answer that?
&&&&
another question, do we need to study the procedure, the equations and the calculations method for the iodine-thiosulfate titrations like
-Finding the purity of potassium Iodate (V)
-Finding the % of Copper in Brass
-Finding the concentration of domestic bleach
I think in iodine-thiosulfate titration you need to calculate the molarity of one of the reactants.
S2O82- = 2I-
1:1 Ratio.
1 Mole : 1 Mole
n=cv.
Post by: Mike Benn on May 08, 2011, 06:48:18 pm
Post by: SkyPilotage on May 08, 2011, 07:30:31 pm
Hey guys..can anyone tell me that How Instantaneous Dipole is produced..?...like how it rises up..?due to the electrons moving around in 3-dimensions..it induces charges on other particles or molecules but its very weak compared to permanent dipoles..
Post by: Mike Benn on May 08, 2011, 07:37:48 pm
due to the electrons moving around in 3-dimensions..it induces charges on other particles or molecules but its very weak compared to permanent dipoles..Thank you very much
Post by: ~ Miss Relina ~ on May 09, 2011, 04:45:18 pm
Post by: Amelia on May 09, 2011, 05:11:53 pm
in both attachrmnt plz notice Q 6b in JAn 2009 and Q 5 in JAn 2010 and tell me diiference why in 2009 it was mean bond enthalpy and why in 2010 it was equation A
In ppr. 2010, Q5 - the question is to find bond enthalphy for C-H (one carbon bonded with one hydrogen).
In ppr. 2009, Q6 - it states the mean bond enthalphy for CH4, (Carbon bonded with four hydrogens)
Post by: ~ Miss Relina ~ on May 09, 2011, 05:15:27 pm
In ppr. 2010, Q5 - the question is to find bond enthalphy for C-H (one carbon bonded with one hydrogen).but in Q5 it said mean bond enthalpy so should it be just one bond and why it is not C
In ppr. 2009, Q6 - it states the mean bond enthalphy for CH4, (Carbon bonded with four hydrogens)
Post by: Amelia on May 09, 2011, 05:25:39 pm
but in Q5 it said mean bond enthalpy so should it be just one bond and why it is not C
It said only C-H bond. It would have been 'C' if the question said - find mean bond enthalphy for 'CH4' molecule.
Post by: ~ Miss Relina ~ on May 09, 2011, 11:00:44 pm
It said only C-H bond. It would have been 'C' if the question said - find mean bond enthalphy for 'CH4' molecule.Thanks plz here Q 10
Post by: Amii on May 10, 2011, 12:07:00 am
Thanks plz here Q 10-First convert the volume from cm3 to dm3.
-Then find the number of moles.
-Then multiply the number of moles with Avagadro constant
-Then multiply the answer with the total number of ions present
a) 10 cm3 = 0.01 dm3
No. of moles = C X V = 0.1 X 0.01 = 0.001 moles
=0.001 X 6.022 x10^23
=6.022X10^20
6.022X10^20 X 2 (Total number of ions present)
=1.204X10^21
b) 20 cm3 = 0.02 dm3
No. of moles = C X V = 0.05 X 0.02 = 0.001 moles
=0.001 X 6.022 x10^23
=6.022X10^20
6.022X10^20 X 2 (Total number of ions present)
=1.204X10^21
c) 20cm3= 0.02 dm3
No. of moles = C X V = 0.05 X 0.02 = 0.001 moles
=0.001 X 6.022 x10^23
=6.022X10^20
6.022X10^20 X 3 (Total number of ions present)
=1.8066 X10^21
d) 13.33 cm3 = 0.01333 moles
No. of moles = C X V = 0.05 X 0.01333 = 6.665X10^-4 moles
= 6.665X10^-4 X 6.022 X10^23
=4.013663 x 10^ 20
4.013663 x 10^ 20 x 3(Total number of ions present)
=1.204 X 10^21
Take care :D
Post by: ~ Miss Relina ~ on May 10, 2011, 08:33:14 am
-First convert the volume from cm3 to dm3.that is what i misse up :o
-Then find the number of moles.
-Then multiply the number of moles with Avagadro constant
-Then multiply the answer with the total number of ions present
a) 10 cm3 = 0.01 dm3
No. of moles = C X V = 0.1 X 0.01 = 0.001 moles
=0.001 X 6.022 x10^23
=6.022X10^20
6.022X10^20 X 2 (Total number of ions present)
=1.204X10^21
b) 20 cm3 = 0.02 dm3
No. of moles = C X V = 0.05 X 0.02 = 0.001 moles
=0.001 X 6.022 x10^23
=6.022X10^20
6.022X10^20 X 2 (Total number of ions present)
=1.204X10^21
c) 20cm3= 0.02 dm3
No. of moles = C X V = 0.05 X 0.02 = 0.001 moles
=0.001 X 6.022 x10^23
=6.022X10^20
6.022X10^20 X 3 (Total number of ions present)
=1.8066 X10^21
d) 13.33 cm3 = 0.01333 moles
No. of moles = C X V = 0.05 X 0.01333 = 6.665X10^-4 moles
= 6.665X10^-4 X 6.022 X10^23
=4.013663 x 10^ 20
4.013663 x 10^ 20 x 3(Total number of ions present)
=1.204 X 10^21
Take care :D
Thanks alot :)
Post by: red_911 on May 10, 2011, 02:56:00 pm
Post by: Assi1993 on May 10, 2011, 09:11:06 pm
Post by: The Golden Girl =D on May 11, 2011, 06:57:13 am
what are the general reasons in chemistry paper 3b of why the reation does not produce a 100% yield ?
I guess these are the general ones;
loss in transfer.
Some remained in the beaker/flask/funnel.
in case they're organic reagents then it's because they're volatile.
Post by: **RoRo** on May 11, 2011, 08:52:41 am
Is it methoxypropaneamine OR Aminomethoxypropane?
Post by: Master_Key on May 11, 2011, 08:54:21 am
What's the name of this compound, CH3CH2CH2OCH2NH2?Name of functional group is placed last.
Is it methoxypropaneamine OR Aminomethoxypropane?
Like propanenitrile.
Post by: EMO123 on May 11, 2011, 08:59:39 am
What's the name of this compound, CH3CH2CH2OCH2NH2?i think it is Methoxypopaneamine :-\
Is it methoxypropaneamine OR Aminomethoxypropane?
Post by: **RoRo** on May 11, 2011, 09:18:09 am
i think it is Methoxypopaneamine :-\
OR Methoxyaminopropane?
Post by: mdwael on May 11, 2011, 04:32:25 pm
sodium to argon (Na to Ar).
Post by: **RoRo** on May 11, 2011, 04:40:29 pm
Explain why the first ionization energies generally increase across the period
sodium to argon (Na to Ar).
As you go across a period,
1. The charge on the nucleus increases, the number of protons in the nucleus increases, so the nucleus becomes more positively charged, so the electrons are attracted more strongly to the nucleus, so more energy would be required to remove an electron and hence the first ionization energy is greater.
2. Due to the increase in the nuclear charge and the stronger attraction, the electrons are closer to the nucleus and hence they are attracted more strongly than the ones further away, so more energy would be required to remove an electron and hence the first ionization energy is greater.
Post by: Aadeez || Zafar on May 11, 2011, 05:19:57 pm
Explain why the first ionization energies generally increase across the period
sodium to argon (Na to Ar).
see this really helpfull
http://www.khanacademy.org/v/periodic-table-trends--ionization-energy?p=Chemistry
Post by: mdwael on May 11, 2011, 05:58:20 pm
magnesium
Post by: Amelia on May 11, 2011, 06:12:31 pm
Explain why the first ionization energy of aluminium is less than that of
magnesium
Compare their electronic configurations
Magnesium : 1s2 2s2 2p6 3s2
Aluminium: 1s2 2s2 2p6 3s2 3p1
The outer electron in aluminium is in a p sub-level. This is higher in energy than the outer electron in magnesium, which is in an s sub-level, so less energy is needed to remove it.
Post by: Aadeez || Zafar on May 11, 2011, 07:35:03 pm
Compare their electronic configurationsya she is absoleutly right
Magnesium : 1s2 2s2 2p6 3s2
Aluminium: 1s2 2s2 2p6 3s2 3p1
The outer electron in aluminium is in a p sub-level. This is higher in energy than the outer electron in magnesium, which is in an s sub-level, so less energy is needed to remove it.
Post by: guMnam on May 13, 2011, 10:30:37 am
Post by: The Golden Girl =D on May 13, 2011, 12:10:40 pm
why graphite conducts electricity in only one direction while other metals conduct it in all directions ??
I believe it's because it has London forces between the layers and covalent bonding within the layer.
Not sure of the details which is why I didn't mention them.
Post by: guMnam on May 13, 2011, 12:20:26 pm
Post by: Malak on May 13, 2011, 07:34:38 pm
metalic bonding within the layer :S... macro molecule . stong covalent bonds between carbon atom,.. each atom is bonded wid 3 other carbon atoms..tht means 1 e is free.. tht allows the conduction.... the point is.. y only one direction ???
The conductivity in graphite is direction dependent
When talking about In plane (parallel): There is one delocalized electron per carbon within a layer therefore electrons can move easily along layers
They wont conduct electricity in Perpendicular plane: There is an energy gap between the layers ( like one layer which is above and the other below it) which is too large for electron transfer.
So it is in one direction only that is along layers
Post by: Malak on May 14, 2011, 02:19:56 pm
How to balance ionic equations using oxidation number
And specifically i have a problem with this one
IO4- + I- + H+ --> I2 + H2O
Thx
Post by: The Golden Girl =D on May 14, 2011, 02:41:24 pm
Can anyone explain me briefly
How to balance ionic equations using oxidation number
And specifically i have a problem with this one
IO4- + I- + H+ --> I2 + H2O
Thx
I hope this helps ;
http://www.chemguide.co.uk/inorganic/redox/equations.html
http://www.sparknotes.com/testprep/books/sat2/chemistry/chapter6section3.rhtml
http://www.chemistry.co.nz/chemequa.htm
http://blip.tv/file/3305442
GG :)
Post by: Amelia on May 14, 2011, 04:54:17 pm
And specifically i have a problem with this oneHere (http://in.answers.yahoo.com/question/index?qid=20100518013119AArEiwH)
IO4- + I- + H+ --> I2 + H2O
Thx
. :)
Post by: Malak on May 14, 2011, 06:22:04 pm
Can anyone state general errors and precautions for acid base titration
thx
Post by: EMO123 on May 15, 2011, 07:02:55 am
^^ Thx bothhttp://www.khanacademy.org/v/acid-base-titration?p=Chemistry
Can anyone state general errors and precautions for acid base titration
thx
hope it helps(May be)
Post by: Malak on May 15, 2011, 01:14:04 pm
My vertical line was at 3 min not at 3.5 as the ms says..
Its Q2 from may 2009 3b
Thx
Post by: ~ Miss Relina ~ on May 15, 2011, 01:50:13 pm
How do you draw the line on the graph?as u added the i think reactant zinc or what ever at 3.5 so u should extend the line from there to get the x temp reached :D
My vertical line was at 3 min not at 3.5 as the ms says..
Its Q2 from may 2009 3b
Thx
Post by: Malak on May 15, 2011, 01:58:32 pm
as u added the i think reactant zinc or what ever at 3.5 so u should extend the line from there to get the x temp reached :DOh thx...Ugh i should read the question carefully :D
Post by: Assi1993 on May 15, 2011, 03:54:38 pm
>whats the relation of Gibbs free energy with the solubility and spontanity of the reaction?
>in the attachment, the answer of activation energy is supposed 2 be -78kJmol^-1 but idk how its calculated!
Post by: Assi1993 on May 15, 2011, 03:57:59 pm
Post by: EMO123 on May 16, 2011, 09:23:50 am
i have a few doubts...i think it is done by hess law
>whats the relation of Gibbs free energy with the solubility and spontanity of the reaction?
>in the attachment, the answer of activation energy is supposed 2 be -78kJmol^-1 but idk how its calculated!
hope it may be right
Post by: Malak on May 16, 2011, 01:17:11 pm
http://www.xtremepapers.me/Edexcel/Advanced%20Level/Chemistry/2007%20Jan/6243_02_que_00070118.pdf (http://www.xtremepapers.me/Edexcel/Advanced%20Level/Chemistry/2007%20Jan/6243_02_que_00070118.pdf)
Thx
Post by: Aadeez || Zafar on May 16, 2011, 08:54:20 pm
Q7 from Jan 07srry i m ot familiar with this type of question
http://www.xtremepapers.me/Edexcel/Advanced%20Level/Chemistry/2007%20Jan/6243_02_que_00070118.pdf (http://www.xtremepapers.me/Edexcel/Advanced%20Level/Chemistry/2007%20Jan/6243_02_que_00070118.pdf)
Thx
Post by: The Golden Girl =D on May 16, 2011, 09:03:20 pm
P.S. sorry ,Can't help.
Post by: Malak on May 17, 2011, 06:05:14 pm
Why is the answer B?
I thought that since cyclohexanol will have OH bond therefore it would dissovle in water ? :S
Thx
Post by: The Golden Girl =D on May 17, 2011, 08:21:40 pm
Post by: Malak on May 17, 2011, 08:53:09 pm
Attached now...
Post by: elemis on May 18, 2011, 04:43:32 am
Oh Sorry...
Attached now...
Although, cyclohexane does have hydrogen bonds it would NOT be a very polar compound due to the massive carbon ring it contains.
Hence, it wouldnt be able to break the Hydrogen bonds between water.
Effectively, propanone is the best answer.
Post by: SkyPilotage on May 18, 2011, 09:43:08 am
Although, cyclohexane does have hydrogen bonds it would NOT be a very polar compound due to the massive carbon ring it contains.So cyclohexane is less soluble in butanone for example? cz it has more Van-der-waals so its harder to break right?
Hence, it wouldnt be able to break the Hydrogen bonds between water.
Effectively, propanone is the best answer.
Post by: NightHawkerr on May 18, 2011, 08:01:34 pm
Thanks, you guys are the best :D
Post by: Malak on May 18, 2011, 08:10:41 pm
Hi ya'll. Im doing AS Chem, and i was wondering if you guys could help me out.. What should I be studying for Unit 3 Alt. to Practical? Are there like specific experiments I should concentrate more on? & the syllabus has changed since 2008 right, that means I should only study past papers from 2009 and 2010?
Thanks, you guys are the best :D
I suggest that you should check the specification which mentions the experiments you should know and study according to that.
Also memorise some common test, like for gases and organic test in the syllabus, colour changes etc.
And do learn the techniques for titration it always comes up
And some basic calculations like moles and stuff from IG
Post by: The Golden Girl =D on May 19, 2011, 07:39:23 am
Post by: Uchia on May 19, 2011, 07:51:54 am
chromotography is for the A2 only not the AS
Post by: ksitna on May 19, 2011, 02:35:59 pm
Post by: elemis on May 19, 2011, 02:37:58 pm
can you please tell me where i can find the chemistry specification?
http://www.edexcel.com/migrationdocuments/GCE%20New%20GCE/International-spec-Chemistry.pdf (http://www.edexcel.com/migrationdocuments/GCE%20New%20GCE/International-spec-Chemistry.pdf)
Post by: Uchia on May 19, 2011, 03:01:32 pm
download it from here
http://www.edexcel.com/quals/gce/gce08/chemistry/Pages/default.aspx
Post by: ksitna on May 19, 2011, 03:04:44 pm
so much!
Post by: NidZ- Hero on May 20, 2011, 06:06:17 am
Post by: guMnam on May 20, 2011, 07:25:22 am
Post by: The Golden Girl =D on May 20, 2011, 07:32:27 am
Hey guys why does only tertiary doesnt react while secondary n primary does wid acidified postassium dichromate
you mean tertiary Alcohol ... well it's because the carbon that's bonded to the OH group is bonded to THREE other carbons where as in the secondary alcohol the carbon bonded to the OH group is only bonded to TWO carbons and a HYDROGEN ..... Remember one of the definitions of Oxidation is loss of hydrogen and since the tertiary is NOT bonded to ANY HYDROGENS that is why the tertiary is NEVER going to get oxidized ;)
I hope you got it :)
Post by: Uchia on May 20, 2011, 09:36:02 am
Post by: 7d on May 20, 2011, 01:22:57 pm
Post 'em all here!!!!
I do Edexcel AS chemistry!
well
im studying chem and i was wondering if anyone cn give me some advice on how to study organic chemistry and unit3
the problem with unit 3 is the detailed questions following the experiments
is there any site where i cn find experiments and their details and unit3 revision in general ?!
i already have the cgp revision guide...
also
in the syllabus it says :
explain why a metal halide and concentrated sulphuric acid should not be used when making a bromoalkane or an iodoalkane
treatment of haloalkanes iwth water containing dissolved silver nitrate ??
demonstrate an understanding of why it is helpful to classify reagents
help/?? i dont understand these topics any help will be appreciated
thank you so much :)
Post by: elemis on May 20, 2011, 01:28:48 pm
You'd be left with very little Hydrogen Bromide or Hydrogen Iodide which is required to form a bromoalkane or iodoalkane.
Silver Nitrate reacts with a chloroalkane to form a white ppt., a bromoalkane to forma a cream ppt. and a iodoalkane to form a yellow ppt.
Post by: guMnam on May 20, 2011, 03:45:04 pm
just a lil confusion... wats the difernce in a free radical and a -ve ion ??
Post by: The Golden Girl =D on May 20, 2011, 03:49:34 pm
err...
just a lil confusion... wats the difernce in a free radical and a -ve ion ??
free radical is a specie that has an unpaired electron where as -ve ion is an atom that has one less electron
I hope I helped :)
Post by: NightHawkerr on May 20, 2011, 03:50:19 pm
well
im studying chem and i was wondering if anyone cn give me some advice on how to study organic chemistry and unit3
the problem with unit 3 is the detailed questions following the experiments
is there any site where i cn find experiments and their details and unit3 revision in general ?!
i already have the cgp revision guide...
also
in the syllabus it says :
explain why a metal halide and concentrated sulphuric acid should not be used when making a bromoalkane or an iodoalkane
treatment of haloalkanes iwth water containing dissolved silver nitrate ??
demonstrate an understanding of why it is helpful to classify reagents
help/?? i dont understand these topics any help will be appreciated
thank you so much :)
Can you please post the syllabus link here..? Thankyou.. :)
Post by: guMnam on May 20, 2011, 03:55:37 pm
free radical is a specie that has an unpaired electron where as -ve ion is an atom that has one less electronone more electron *
I hope I helped :)
see the problem is tht they both have one more elctron than normal .. the way i see it ... in an ion the electron is in the orbitals... and in free radical its not :S
for eg.
cl- and .cl
Post by: Malak on May 20, 2011, 04:13:52 pm
one more electron *
see the problem is tht they both have one more elctron than normal .. the way i see it ... in an ion the electron is in the orbitals... and in free radical its not :S
for eg.
cl- and .cl
They both dont have one more electron thn normal..
A negative ion is the one which has Gained one electron but
a free radical is just a specie with an unpaired electron for e.g all the halogens, they all have one unpaired electron..its not about losing or gaining electron here..
Post by: guMnam on May 20, 2011, 05:12:33 pm
They both dont have one more electron thn normal.... wen something gains an electron tht means tht it has one more electron (than its ground state) ??-.-
A negative ion is the one which has Gained one electron but
a free radical is just a specie with an unpaired electron for e.g all the halogens, they all have one unpaired electron..its not about losing or gaining electron here..
so all molecules like Li, H ,Na , K(who have one unpaired e-)are also free radicals ?
Post by: ~ Miss Relina ~ on May 21, 2011, 07:10:49 am
Post by: elemis on May 21, 2011, 07:12:33 am
Unit 2 Jan 2011 need Q:15 pplw
Attach the file.
Post by: **RoRo** on May 21, 2011, 09:06:16 am
Thanks a lot! :)
Post by: EMO123 on May 21, 2011, 09:17:42 am
When they ask us to draw the ionic structure of NaCl, we need to do that in 3D, right? How do you draw it? Can someone please upload a photo, or link me with one?may be like this it also works
Thanks a lot! :)
(http://www.hull.ac.uk/chemistry/intro_inorganic/images/nacl.jpg)
Post by: **RoRo** on May 21, 2011, 09:21:39 am
may be like this it also works
(http://www.hull.ac.uk/chemistry/intro_inorganic/images/nacl.jpg)
That'd take ages for me to draw, thanks! :)
Post by: EMO123 on May 21, 2011, 09:37:02 am
That'd take ages for me to draw, thanks! :)oh that was easy and
glad to help
Post by: The Golden Girl =D on May 21, 2011, 11:53:27 am
https://studentforums.biz/revison-notes/useful-websites/45/
GG :D
Post by: Malak on May 21, 2011, 12:10:43 pm
I've just uploaded something for the coming Unit 3 exam , check it over here ;Thx :D
https://studentforums.biz/revison-notes/useful-websites/45/
GG :D
Adding on one more
http://chem-ilp.net/ (http://chem-ilp.net/)
Great website for practical techniques
Post by: Malak on May 21, 2011, 12:47:49 pm
Why is the temperature change double? There are same no. moles in both :s
Thx
Post by: NightHawkerr on May 21, 2011, 02:41:45 pm
Does anyone have the link to AS chem Unit 3B Jan 2011? I cant seem to find it anywhere.. ;/
merci ^^
Post by: ~ Miss Relina ~ on May 21, 2011, 03:22:46 pm
Unit 2 Jan 2011 need Q:15 pplw
Post by: ~ Miss Relina ~ on May 21, 2011, 03:23:15 pm
Thanks GG for the notes :Dhere
Does anyone have the link to AS chem Unit 3B Jan 2011? I cant seem to find it anywhere.. ;/
merci ^^
Post by: Malak on May 21, 2011, 03:34:49 pm
Sorry..whats pplw?
:S
Q15 which part?
Post by: NightHawkerr on May 21, 2011, 06:11:19 pm
& What's the difference between Mean bond enthalpy and just standard bond enthalpy? Thanks alot!
Post by: ~ Miss Relina ~ on May 21, 2011, 06:37:17 pm
Sorry..whats pplw?pplw was a mis typing
:S
Q15 which part?
Q 15 part b
Post by: Malak on May 21, 2011, 06:37:36 pm
In some past papers I've seen that if we have to find the enthalpy change, they do delta H of reactants - delta H of products, when Ive studied that to find delta H its delta H of prod - delta H of reactants.. When is this not the case? I dont remember what past paper it is actually from, but help would be appreciated. :)
& What's the difference between Mean bond enthalpy and just standard bond enthalpy? Thanks alot!
Its Products - reactants when you are finding it for Enthalpy of Formation
And for Enthalpy of combustion its reactants - products
Mean bond enthalpy is the Average value for that bond whereas the other one is particularly for that bond in that compound
For eg C-H bond in methane is different from in ethanol but mean value of C-H bond is used assuming they are all the same
Hope u get it?
Post by: NightHawkerr on May 21, 2011, 06:44:38 pm
Its Products - reactants when you are finding it for Enthalpy of Formation
And for Enthalpy of combustion its reactants - products
Mean bond enthalpy is the Average value for that bond whereas the other one is particularly for that bond in that compound
For eg C-H bond in methane is different from in ethanol but mean value of C-H bond is used assuming they are all the same
Hope u get it?
Hmm I get it thanks alot :D
And for the Hess's Law, it's reactant-products?
Post by: Malak on May 21, 2011, 06:45:47 pm
pplw was a mis typing
Q 15 part b
b (i) - appropriate readings are the ones which are concordant so, (11.40 + 11.20)/2 = 11.30
b-ii no. of moles is simply n = cv, so 0.300 * 11.3 = 0.00339 mol
iii- the ratio is 1 --> 1 so same no. of moles of HCl are used i.e 0.00339
iv- in 10 cm3 moles are 0.00339 so in 100 there will be 0.0339 (just * 10)
M not sure if you need the rest of parts as well?
Post by: The Golden Girl =D on May 21, 2011, 08:01:14 pm
2010 Jan Question 3d (v) and (vi)
Why is the temperature change double? There are same no. moles in both :s
Thx
ang3l , was this doubt cleared out ?
if not send me a PM ,and I'll answer you tomorrow inshAllah :)
@NightHawkerr : You're Welcome :)
Post by: ~ Miss Relina ~ on May 21, 2011, 09:00:46 pm
2010 Jan Question 3d (v) and (vi)ya i had same doubt too
Why is the temperature change double? There are same no. moles in both :s
Thx
Post by: ~ Miss Relina ~ on May 21, 2011, 09:03:05 pm
b (i) - appropriate readings are the ones which are concordant so, (11.40 + 11.20)/2 = 11.30well what i understood for iii is that they said left is that means remainig or whT soory for annoying u but this was my doubt Thanks
b-ii no. of moles is simply n = cv, so 0.300 * 11.3 = 0.00339 mol
iii- the ratio is 1 --> 1 so same no. of moles of HCl are used i.e 0.00339
iv- in 10 cm3 moles are 0.00339 so in 100 there will be 0.0339 (just * 10)
M not sure if you need the rest of parts as well?
Post by: studz on May 21, 2011, 09:31:30 pm
i wanna know what are the key things to remember and where can i get papers for practicing
we did not do unit 6 at school :(
Post by: Blizz_rb93 on May 21, 2011, 09:57:28 pm
2NH3 (aq) + H2SO4 (aq) -> (NH4)SO4 (aq)
a) Calculate the theoretical maximum yield that can be obtained by reacting 25.0 cm3 of 2.0mol dm-3 ammonia solution with an excess of sulfuric acid.
b) If the actual mass obtained was 3.12g, calculate the percentage yield and suggest reasons why the yield is less than 100%
can anyone help me with this asap please and id just like to know what are the exact methods of solving a question regarding this topic
Thank you :)
Post by: Malak on May 21, 2011, 10:16:14 pm
A student prepared a sample of the fertilizer ammonium sulfate by adding ammonia solution to sulfuric acid :
2NH3 (aq) + H2SO4 (aq) -> (NH4)SO4 (aq)
a) Calculate the theoretical maximum yield that can be obtained by reacting 25.0 cm3 of 2.0mol dm-3 ammonia solution with an excess of sulfuric acid.
b) If the actual mass obtained was 3.12g, calculate the percentage yield and suggest reasons why the yield is less than 100%
can anyone help me with this asap please and id just like to know what are the exact methods of solving a question regarding this topic
Thank you :)
No. of moles of ammonia : 25/1000 * 2.0 = 0.05 mol
eq. (should be (NH4)2SO4) shows that 2 moles of NH3 form 1 mole of the product
So 0.025 moles of product are formed
molar mass of ammonium sulfate = 132.1
therefore mass formed will be 132.1 * 0.025 = 3.3025
(b) % yield = actual mass / maximum possible
so %yield = (3.12 / 3.3025) * 100
= 94.5 %
And reasons could be :
Reactants are impure
Product left behind on apparatus
Human error
I just did the calculations, if u have any doubt then ask:)
Post by: Malak on May 21, 2011, 11:37:24 pm
20 cm3 of sulfuric acid, concentration 0.25 mol dm–3, was neutralized in a titration with barium hydroxide, concentration 0.50 mol dm–3. The equation for the reaction is
Ba(OH)2(aq) + H2SO4(aq) ? BaSO4(s) + 2H2O(l)
During the titration, the barium hydroxide was added until it was present in excess.
The electrical conductivity of the titration mixture
A increased steadily.
B decreased steadily.
C increased and then decreased.
D decreased and then increased.
its 2010 Jan Q10 unit 2
Post by: The Golden Girl =D on May 22, 2011, 05:49:41 am
2010 Jan Question 3d (v) and (vi)
Why is the temperature change double? There are same no. moles in both :s
Thx
in (v)
Q = m*c*delta T
115 = 25 *4.18 * delta T
so delta T = 11.0
in (iv) delta T = 5.5 => that's given to you at the beginning.
(v) 11.0 , because the same amount of energy present in Half the volume.
(vi) in this one measure the % error for each ;
for (iii) [0.1 * 2]/(5.5) * 100 = 3.64% (two readings hence multiplied by two)
in (vi) = [ 0.2/11 ]* 100 = 1.82%
1.82% in (vi) is LESS THAN 3.64% in (iii)
Answer ; (v) will have LESS error because delta T is TWICE bigger.
I hope you got it girls :)
Post by: The Golden Girl =D on May 22, 2011, 05:56:31 am
Anyone doing chemistry unit 6?? its on the 7th of june right
i wanna know what are the key things to remember and where can i get papers for practicing
we did not do unit 6 at school :(
Check this ;
https://studentforums.biz/pastpapers/edexcel-unit-6b-(6ch08)-practicals/ (https://studentforums.biz/pastpapers/edexcel-unit-6b-(6ch08)-practicals/)
Post by: guMnam on May 22, 2011, 09:31:13 am
Post by: Malak on May 22, 2011, 11:06:14 am
june 2009 unit 1... q 5... how do fing the moles of so4^2- ??
No. of ions = moles * Avogadro's constant * no. of those ions in formula
so moles = 17.1/324 = 0.05
now 0.05 * 6.02^23 * 3 (there are 3 molecules of SO4)
= 9.3 ^ 22
D is the answer
Post by: Blizz_rb93 on May 22, 2011, 11:47:23 am
Post by: Malak on May 22, 2011, 11:52:07 am
How much energy is produced when 25cm3 of 1.0 mol dm-3 sulfuric acid is neutralized by 75cm3 of 1.0mol dm-3 NaOH given a temperature rise of 12.1 degrees Celcius?
Energy = mass * Heat capacity * temperature change
100 * 4.12 * 12.1 = 4985.2 J
The heat capacity is given in question, its usually 4.12 or 4.18 not sure so i used 4.12
mass is 100 g as 25 + 75 = 100
Post by: guMnam on May 22, 2011, 01:30:56 pm
No. of ions = moles * Avogadro's constant * no. of those ions in formulaoooh.. i forgt to multipy wid three.. Thanks :)
so moles = 17.1/324 = 0.05
now 0.05 * 6.02^23 * 3 (there are 3 molecules of SO4)
= 9.3 ^ 22
D is the answer
Post by: Blizz_rb93 on May 22, 2011, 01:31:29 pm
i have another question
1 a) How much energy is transferred when 3.0 g MgSO4 (s) is dissolved in 45g water to give a temperature rise of 11.3 degrees Celcius?
b) How much energy is transferred per mole of MgSO4 (s)
Post by: Malak on May 22, 2011, 01:40:35 pm
thank you
i have another question
1 a) How much energy is transferred when 3.0 g MgSO4 (s) is dissolved in 45g water to give a temperature rise of 11.3 degrees Celcius?
b) How much energy is transferred per mole of MgSO4 (s)
(a) Its the same idea
Energy = mass * Heat capacity * temperature change
45 * 4.12 (or whatever is given) * 11.3 = 2095.02 J
(b) no. of moles of MgSO4 = m/mr
So = 3/120.4 = 0.0249
Energy per mole = energy/ moles
so 2095.02 / 0.0249 = 84137 J
u can divide by 1000 if u need the energy in KJ
If u have problem with such questions check out these notes might help u
https://studentforums.biz/revison-notes/q80boy%27s-chemistry-notes-%28edexcel%29/ (https://studentforums.biz/revison-notes/q80boy%27s-chemistry-notes-%28edexcel%29/)
(Energetics part)
Post by: guMnam on May 22, 2011, 01:40:52 pm
thank youa) =45*11.3*4.18 =2125.53 j (2.13 kj)
i have another question
1 a) How much energy is transferred when 3.0 g MgSO4 (s) is dissolved in 45g water to give a temperature rise of 11.3 degrees Celcius?
b) How much energy is transferred per mole of MgSO4 (s)
b)
=3/120.4
=0.0249 mol
=2.13/0.0249
=85.5 kj mol-1
Post by: guMnam on May 22, 2011, 01:41:47 pm
Post by: Malak on May 22, 2011, 01:42:26 pm
lol :P
Haha :D
Post by: NightHawkerr on May 22, 2011, 03:32:43 pm
Post by: elemis on May 22, 2011, 03:33:32 pm
Can someone explain to me the E-Z isomer stuff coming for tomorrow's exam?
http://www.chemguide.co.uk/basicorg/isomerism/geometric.html#top (http://www.chemguide.co.uk/basicorg/isomerism/geometric.html#top)
Keep scrolling down.
Post by: EMO123 on May 22, 2011, 03:35:07 pm
http://www.chemguide.co.uk/basicorg/isomerism/geometric.html#top (http://www.chemguide.co.uk/basicorg/isomerism/geometric.html#top)thanxx ari worthy site
Keep scrolling down.
Post by: Malak on May 22, 2011, 03:44:01 pm
Thx
Post by: The Golden Girl =D on May 22, 2011, 03:53:22 pm
Outline an experiment to demonstrate that catalyst is not used up in a reaction? (practical details not needed)
Thx
weigh the catalyst using top loading balance
filter it back from the mixture after the reaction is complete
wash it with distilled water
dry it and then re-wiegh it
the Mass remains same (unchanged)
GG :)
Post by: NidZ- Hero on May 22, 2011, 04:59:46 pm
(a) A hot aqueous solution of silver nitrate is added to each halogenoalkane. Both
halogenoalkanes react to form a yellow precipitate.
(ii) The isomers have relative molecular mass 169.9. Deduce the molecular formula
of the isomers.
Ok how do we deduce it
Post by: elemis on May 22, 2011, 05:03:46 pm
The question is about two isomeric halogenoalkanes, P and Q.
(a) A hot aqueous solution of silver nitrate is added to each halogenoalkane. Both
halogenoalkanes react to form a yellow precipitate.
(ii) The isomers have relative molecular mass 169.9. Deduce the molecular formula
of the isomers.
Ok how do we deduce it
Is it C3H7I ??
Post by: Malak on May 22, 2011, 05:04:04 pm
The question is about two isomeric halogenoalkanes, P and Q.
(a) A hot aqueous solution of silver nitrate is added to each halogenoalkane. Both
halogenoalkanes react to form a yellow precipitate.
(ii) The isomers have relative molecular mass 169.9. Deduce the molecular formula
of the isomers.
Ok how do we deduce it
It forms yellow ppt so its clear that it is iodide
Now tha rest has to be carbon and hydrgoen so 169.9 - 126.9 = 43
so u have to check how many carbon + Hydrogen can make up 43
three carbons make up 36 + 7 for hydrogen so that make up 43
Post by: Malak on May 22, 2011, 05:05:31 pm
Is it C3H8I ??
not 8 H since if u have 8 H there is no room for I to add
Post by: The Golden Girl =D on May 22, 2011, 05:07:46 pm
The question is about two isomeric halogenoalkanes, P and Q.
(a) A hot aqueous solution of silver nitrate is added to each halogenoalkane. Both
halogenoalkanes react to form a yellow precipitate.
(ii) The isomers have relative molecular mass 169.9. Deduce the molecular formula
of the isomers.
Ok how do we deduce it
R - I = 169.9
and you continue as ang3l mentioned ;)
Post by: Malak on May 22, 2011, 05:09:30 pm
R - I = 169.9lol..:P
and you continue as ang3l mentioned ;)
Ready for 2morrow ?:D
Post by: The Golden Girl =D on May 22, 2011, 05:10:46 pm
lol..:P
Ready for 2morrow ?:D
Yup , Good Luck ;)
Post by: NidZ- Hero on May 22, 2011, 05:20:42 pm
THANKS EVERYONE
Post by: Malak on May 22, 2011, 05:50:49 pm
Do we just say that to allow for cooling
Or is that too vague?
Post by: The Golden Girl =D on May 22, 2011, 06:51:14 pm
Why series of readings are taken for temperature in enthalpy change experiment?
Do we just say that to allow for cooling
Or is that too vague?
you can say to allow for cooling or to compensate for heat loss.
Post by: ~ Miss Relina ~ on May 22, 2011, 07:05:46 pm
needed by syllabus and i donno anthig abt it
Post by: Malak on May 22, 2011, 07:24:17 pm
solubility of simple molecules in different solvents experimentsYou basically just have to know that Polar molecules will dissolve in polar solvents and Non-polar in non-polar solvents.
needed by syllabus and i donno anthig abt it
Like Iodine will dissolve in hydrocarbon solvent but will be partially or insoluble in water
Post by: guMnam on May 22, 2011, 07:46:44 pm
and do we have to learn uses of diferent polymers???
Post by: NightHawkerr on May 22, 2011, 08:05:54 pm
Post by: Malak on May 22, 2011, 08:29:10 pm
If the temperature increases what happens to the peaks( and the broadness) in the infrared spectroscopy? I had this question in my mock exam today, didn't know how to answer it. ;/Is this for A2?
Because I haven't read or seen anything like temperature and IR :S
Post by: NightHawkerr on May 22, 2011, 08:44:45 pm
Is this for A2?
Because I haven't read or seen anything like temperature and IR :S
I dont know, I just saw this in my AS Chem Mock exam today and i got a little worried since I didnt do a question related to IR Spectroscopy for Unit1/Unit3b, Maybe it's comin; for Unit 2 ???
Post by: Malak on May 22, 2011, 09:02:52 pm
I dont know, I just saw this in my AS Chem Mock exam today and i got a little worried since I didnt do a question related to IR Spectroscopy for Unit1/Unit3b, Maybe it's comin; for Unit 2 ???IR is in unit 2 and i have studied it but haven't seen anything regarding temperature affecting peaks or something
Post by: NightHawkerr on May 22, 2011, 09:16:39 pm
IR is in unit 2 and i have studied it but haven't seen anything regarding temperature affecting peaks or something
Okie good, i hope it doesn't come! Thanks. :)
Good luck for your chem Unit 1 and 3 tomorrow!
Post by: Malak on May 22, 2011, 09:20:36 pm
Okie good, i hope it doesn't come! Thanks. :)Thanks :) Good Luck to u too
Good luck for your chem Unit 1 and 3 tomorrow!
By the way i only have 3b :D
Post by: NidZ- Hero on May 22, 2011, 10:27:22 pm
(a) Compound X is a white crystalline solid that dissolves easily in water to form a
clear, colourless solution. X contains one cation and one anion. Complete the table
below.
(5)
Test Observation Inference
(i) Warm solid X with dilute
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A gas was evolved which
turned damp red litmus
paper blue.
Ammonia is formed so
the ammonium ion is
present.
(ii) Add aqueous barium
chloride to a solution of X.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
X contains either
sulfite (sulfate(IV))
or
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
or
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
(iii) Add dilute hydrochloric
acid to the result of
test (ii).
A gas was evolved which
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sulfite (sulfate(IV))
confirmed.
Post by: The Golden Girl =D on May 23, 2011, 06:18:11 am
(a) Compound X is a white crystalline solid that dissolves easily in water to form a
clear, colourless solution. X contains one cation and one anion. Complete the table
below.
(5)
Test Observation Inference
(i) Warm solid X with dilute
. . . . . .Sodium hydroxide solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A gas was evolved which
turned damp red litmus
paper blue.
Ammonia is formed so
the ammonium ion is
present.
(ii) Add aqueous barium
chloride to a solution of X.
. . . . . . . . . . . . . . whit ppt . . . . . . .
X contains either
sulfite (sulfate(IV))
or
. . . . . . . . . . . . . . .Sulphate (6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
or
. . . . . . . . . . . . . . . . . . .Carbonate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
(iii) Add dilute hydrochloric
acid to the result of
test (ii).
A gas was evolved which
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . that turned potassium dichromate from orange to green . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sulfite (sulfate(IV))
confirmed.
Good Luck Everyone :)
Post by: NightHawkerr on May 23, 2011, 10:18:09 am
Thanks :) Good Luck to u too
By the way i only have 3b :D
Ahh luckyyy,I just got over with my 3b, Unit 1 is in 2 hours :-[
Post by: guMnam on May 23, 2011, 04:40:53 pm
Post by: Malak on May 23, 2011, 04:43:00 pm
i hope every one had a nice exam :)mine was good :)
Now have to prepare for unit 3
Post by: guMnam on May 23, 2011, 04:44:51 pm
Post by: Malak on May 23, 2011, 04:45:39 pm
unit 3 :S ^Sorry i meant unit 2 lol..:P
Post by: guMnam on May 23, 2011, 04:50:23 pm
Sorry i meant unit 2 lol..:Phaha.. chem has really messed up ur head :P
lol.. i have to do bio 6 then 2 and then think abt chem unit 2 .. -.- :-\
Post by: Malak on May 23, 2011, 04:53:55 pm
haha.. chem has really messed up ur head :PLol..i guess so :P
lol.. i have to do bio 6 then 2 and then think abt chem unit 2 .. -.- :-\
Oh Good luck..! I have math c2 and them chem 2 so yeah :P but still better situation then urs ::)
Post by: guMnam on May 23, 2011, 04:57:44 pm
Lol..i guess so :Pu sig reminds me of a member named hope =\ *memories*
Oh Good luck..! I have math c2 and them chem 2 so yeah :P but still better situation then urs ::)
Post by: The Golden Girl =D on May 23, 2011, 05:13:32 pm
Post by: Malak on May 23, 2011, 05:16:19 pm
Do u guys mind if I ask, where is that member as in she/he left the forum or what?
Post by: The Golden Girl =D on May 23, 2011, 05:20:15 pm
aw..:)
Do u guys mind if I ask, where is that member as in she/he left the forum or what?
She left but she says she might come back for a while in August.
Here ; https://studentforums.biz/profile/lolo93/
Post by: Malak on May 23, 2011, 05:26:40 pm
She left but she says she might come back for a while in August.
Here ; https://studentforums.biz/profile/lolo93/
Aw..Hopefully since u guys miss her too much :) I think we have one thing in common *Hope* lol..
How was ur exam today?
Eh..am I somehow violating the purpose (chemistry doubts) of this thread ::)..?
Post by: Malak on May 23, 2011, 05:31:38 pm
If a balance accurate to two decimal places was used to record the mass of ethanol collected, what would be the percentage error due to the balance readings if the total mass of ethanol collected was 20.10 g?
Shouldn't it be 0.02%
In ms they multiplied 0.05 by 2, why is that so? u aren't taking 2 readings :S
Post by: The Golden Girl =D on May 23, 2011, 05:34:01 pm
Okay..Back to doubts :D
If a balance accurate to two decimal places was used to record the mass of ethanol collected, what would be the percentage error due to the balance readings if the total mass of ethanol collected was 20.10 g?
Shouldn't it be 0.02%
In ms they multiplied 0.05 by 2, why is that so? u aren't taking 2 readings :S
you are taking TWO readings , mass of ethanol the before burning and mass of ethanol after burning ;)
Post by: Malak on May 23, 2011, 05:36:18 pm
and one more
20 cm3 of sulfuric acid, concentration 0.25 mol dm–3, was neutralized in a titration with barium hydroxide, concentration 0.50 mol dm–3. The equation for the reaction is
Ba(OH)2(aq) + H2SO4(aq) ? BaSO4(s) + 2H2O(l)
(b) During the titration, the barium hydroxide was added until it was present in excess. The electrical conductivity of the titration mixture
A increased steadily.
B decreased steadily.
C increased and then decreased.
D decreased and then increased.
Post by: The Golden Girl =D on May 23, 2011, 05:37:47 pm
^ Oh Thx
and one more
20 cm3 of sulfuric acid, concentration 0.25 mol dm–3, was neutralized in a titration with barium hydroxide, concentration 0.50 mol dm–3. The equation for the reaction is
Ba(OH)2(aq) + H2SO4(aq) ? BaSO4(s) + 2H2O(l)
(b) During the titration, the barium hydroxide was added until it was present in excess. The electrical conductivity of the titration mixture
A increased steadily.
B decreased steadily.
C increased and then decreased.
D decreased and then increased.
I don't remember Questions so tell me which paper is that and what Question :)
Post by: Malak on May 23, 2011, 05:39:38 pm
I don't remember Questions so tell me which paper is that and what Question :)Its Q10 from 2010 Jan
Post by: The Golden Girl =D on May 23, 2011, 05:47:07 pm
Its Q10 from 2010 Jan
It's D ,Because
This is a neutralization reaction and ususally neautralization reactions have LOWEST conductivity which is why it decreases but then the barium hydroxide and sulfuric acid react there are ions present and hence electric conductivity increases.
Ihmm 'll confirm the answer and then get back to you
Post by: The Golden Girl =D on May 23, 2011, 06:34:59 pm
It's D ,Because
This is a neutralization reaction and ususally neautralization reactions have LOWEST conductivity which is why it decreases but then the barium hydroxide and sulfuric acid react there are ions present and hence electric conductivity increases.
Ihmm 'll confirm the answer and then get back to you
I'm sorry for taking too long , I had to call my friend for this.
Hmm it's an follows as Nobody said ;
Look, initially, you've got H2SO4(aq) giving 3 ions
now, when you add barium hydroxide, it will form a precipitate and take out all the sulphate ions in the form of BaSO4(s) and further neutralise the hydrogen ions which fill form 2H2O(l).
oaky? so, at that time, the conductivity decreases.
Now, when all the sulfuric acid is neutralized... barium ions and hydroxide ions will be generated when Ba(OH)2(aq) reacts.
which will lead to an increase in the conductivity.
My friend's/teacher's explanation ;
as bRIUM HYDROXIDE IS added it's ions eat up the acid ions. hence no ions , cuz all ions cancel each other , electrical conductivity falls to 0 ..On more addition of bariium hydroxide , OH- increases , i.e.e the -ve charge increases , hence electrical conductivity increases .
GG :)
Post by: Malak on May 23, 2011, 06:38:26 pm
Thankyou very much :)
Post by: The Golden Girl =D on May 23, 2011, 07:08:22 pm
Post by: ~ Miss Relina ~ on May 23, 2011, 08:57:05 pm
Post by: NightHawkerr on May 23, 2011, 10:06:41 pm
>:( :( :'( unit 1
I know. :(
Post by: guMnam on May 23, 2011, 10:24:48 pm
Thanks i had the same doubt .. but i got the corerect ans AND A rong explanation :P
I'm sorry for taking too long , I had to call my friend for this.
Hmm it's an follows as Nobody said ;
Look, initially, you've got H2SO4(aq) giving 3 ions
now, when you add barium hydroxide, it will form a precipitate and take out all the sulphate ions in the form of BaSO4(s) and further neutralise the hydrogen ions which fill form 2H2O(l).
oaky? so, at that time, the conductivity decreases.
Now, when all the sulfuric acid is neutralized... barium ions and hydroxide ions will be generated when Ba(OH)2(aq) reacts.
which will lead to an increase in the conductivity.
My friend's/teacher's explanation ;
as bRIUM HYDROXIDE IS added it's ions eat up the acid ions. hence no ions , cuz all ions cancel each other , electrical conductivity falls to 0 ..On more addition of bariium hydroxide , OH- increases , i.e.e the -ve charge increases , hence electrical conductivity increases .
GG :)
Post by: The Golden Girl =D on May 24, 2011, 06:42:13 am
Post by: **RoRo** on May 24, 2011, 07:21:34 am
Post by: The Golden Girl =D on May 24, 2011, 07:27:53 am
Good Luck ;)
Post by: **RoRo** on May 24, 2011, 08:17:38 am
Only the Organic chapter and have a general Idea of the graphs for the exo and endo rxns.
Good Luck ;)
Expected so [organic]!
Thank you & good luck to you too! :)
Post by: The Golden Girl =D on May 24, 2011, 08:18:30 am
Post by: Blizz_rb93 on May 24, 2011, 11:36:25 am
and
Suggest why chlorine-based insecticides last a long time in the soil?
if anyone knows where i can get the teachers book for the edexcel AS chemistry, that would be very helpful
Thank you :)
Post by: Master_Key on May 24, 2011, 02:17:08 pm
Give 2 reasons why chlorinated hydrocarbons are not used today in fire extinguishers?Chlorinated HC cause damage to ozone layer. They are stable so reach ozone layer quickly.
and
Suggest why chlorine-based insecticides last a long time in the soil?
if anyone knows where i can get the teachers book for the edexcel AS chemistry, that would be very helpful
Thank you :)
Chlorine radical are formed in fire.
Post by: NidZ- Hero on May 25, 2011, 07:05:55 am
Post by: EMO123 on May 25, 2011, 07:29:55 am
Whats the difference between Nuclear charge and effective nuclear charge?http://answers.yahoo.com/question/index?qid=20101004142249AAzpUkI
hope it helped
Post by: NidZ- Hero on May 25, 2011, 07:36:45 am
http://answers.yahoo.com/question/index?qid=20101004142249AAzpUkI
hope it helped
I read this before... but know i understood
well its lke this
a fluorine atom has an electronic structure of 1s2 2s2 2px2 2py2 2pz1. It has 9 protons in the nucleus.
The incoming electron enters the 2-level, and is screened from the nucleus by the two 1s2 electrons. It therefore feels a net attraction from the nucleus of 7+ (9 protons less the 2 screening electrons).
By contrast, chlorine has the electronic structure 1s2 2s2 2p6 3s2 3px2 3py2 3pz1. It has 17 protons in the nucleus.
But again the incoming electron feels a net attraction from the nucleus of 7+ (17 protons less the 10 screening electrons in the first and second levels).
Nucleur charge = proton number
Effective nuclear charge = Nucleur charge- no.of screening electrons
is that rght ?
Post by: EMO123 on May 25, 2011, 07:50:39 am
I read this before... but know i understoodya it is right
well its lke this
a fluorine atom has an electronic structure of 1s2 2s2 2px2 2py2 2pz1. It has 9 protons in the nucleus.
The incoming electron enters the 2-level, and is screened from the nucleus by the two 1s2 electrons. It therefore feels a net attraction from the nucleus of 7+ (9 protons less the 2 screening electrons).
By contrast, chlorine has the electronic structure 1s2 2s2 2p6 3s2 3px2 3py2 3pz1. It has 17 protons in the nucleus.
But again the incoming electron feels a net attraction from the nucleus of 7+ (17 protons less the 10 screening electrons in the first and second levels).
Nucleur charge = proton number
Effective nuclear charge = Nucleur charge- no.of screening electrons
is that rght ?
Post by: Master_Key on May 25, 2011, 08:20:05 am
I read this before... but know i understoodIts shielding electrons.
well its lke this
a fluorine atom has an electronic structure of 1s2 2s2 2px2 2py2 2pz1. It has 9 protons in the nucleus.
The incoming electron enters the 2-level, and is screened from the nucleus by the two 1s2 electrons. It therefore feels a net attraction from the nucleus of 7+ (9 protons less the 2 screening electrons).
By contrast, chlorine has the electronic structure 1s2 2s2 2p6 3s2 3px2 3py2 3pz1. It has 17 protons in the nucleus.
But again the incoming electron feels a net attraction from the nucleus of 7+ (17 protons less the 10 screening electrons in the first and second levels).
Nucleur charge = proton number
Effective nuclear charge = Nucleur charge- no.of screening electrons
is that rght ?
Chlorine has same E.N.C. The electrons are held far and thus the ionisation energies and properties like that are less when compared to Fluorine. For attraction you need to consider both.
Effective nuclear charge and distance from nucleus.
Post by: **RoRo** on May 25, 2011, 11:28:24 am
& when the branching in alkanes increases, the melting point increases or decreases and why?
Thank you :)
Post by: Malak on May 25, 2011, 12:29:54 pm
Question, are we supposed to know the ionic equations for the common oxidizing/reducing agents like Manganate (VII), Dichromate (VI), Hydrogen peroxide, concentrated sulphuric acid, potassium iodide, etc?I dont think u need to memories those equations, but then u should know how to write ionic equations generally in case it comes up.
& when the branching in alkanes increases, the melting point increases or decreases and why?
Thank you :)
When branching increases the melting point decreases because the atoms are less packed together and therefore the intermolecular forces are weaker
Post by: **RoRo** on May 25, 2011, 01:42:04 pm
I dont think u need to memories those equations, but then u should know how to write ionic equations generally in case it comes up.
When branching increases the melting point decreases because the atoms are less packed together and therefore the intermolecular forces are weaker
Great! Thank you very much! ;D
Post by: NidZ- Hero on May 25, 2011, 02:47:58 pm
Is it that the amount of hydration energy released compensates for the amount of energy required for the lattice energy when the compound break :S
Post by: Malak on May 25, 2011, 03:11:42 pm
The solubity of a compoud depends on whatYes, both should balance each other out, this why ionic substances dissolve in water 'cause the energy is balanced out
Is it that the amount of hydration energy released compensates for the amount of energy required for the lattice energy when the compound break :S
Post by: NidZ- Hero on May 25, 2011, 03:16:18 pm
Yes, both should balance each other out, this why ionic substances dissolve in water 'cause the energy is balanced outAnd one web sorce said that they r polar so dissolve in polar solvents lke water n ethanol
Post by: Malak on May 25, 2011, 03:23:00 pm
And one web sorce said that they r polar so dissolve in polar solvents lke water n ethanol
Generally:
Polar dissolves in polar
Non-polar dissolves in non polar :D
Post by: NidZ- Hero on May 25, 2011, 03:39:24 pm
In my Edxcel book its says : the larger the negative ion and large its charge
Why does charge has to be large
Post by: Malak on May 25, 2011, 04:36:42 pm
hey one more thng why does small cation is good in polarizing and large anion get polarizedIf a cation is small i.e. it has small radius then its has a greater charge density.
In my Edxcel book its says : the larger the negative ion and large its charge
Why does charge has to be large
For cations: Small radius + high charge = greater charge density
For anions: The larger it is (large radius) the more easily it gets polarised
m not sure why ur book mentions charge for anion 'cause in my book it says that for anion it solely depends on the radius.
But what i can guess ur book means is --> if the charge is higher (more negative), the anion is more polarisable as more negative charge means more electrons are added to it and so the radius gets larger
Post by: NidZ- Hero on May 25, 2011, 05:00:42 pm
If a cation is small i.e. it has small radius then its has a greater charge density.Same even i gt gt confused abut the charge on the anion
For cations: Small radius + high charge = greater charge density
For anions: The larger it is (large radius) the more easily it gets polarised
m not sure why ur book mentions charge for anion 'cause in my book it says that for anion it solely depends on the radius.
But what i can guess ur book means is --> if the charge is higher (more negative), the anion is more polarisable as more negative charge means more electrons are added to it and so the radius gets larger
Post by: NidZ- Hero on May 25, 2011, 05:07:20 pm
how does hydroxide ions make the solution basic or alkali? ???
Post by: The Golden Girl =D on May 25, 2011, 05:12:15 pm
Generally:
Polar dissolves in polar
Non-polar dissolves in non polar :D
Acetone is the only solvent that dissolves in both ;)
Post by: Amelia on May 25, 2011, 05:40:21 pm
Thanks Angel :D
how does hydroxide ions make the solution basic or alkali? ???
A solution is a base or alkali if it contains and releases the hydroxide ions (OH-). ;)
Post by: sharleen07 on May 25, 2011, 08:00:27 pm
Post by: The Golden Girl =D on May 25, 2011, 08:17:58 pm
any suggestions about what to study for the chemistry A2 practicals (edexcel)??
Check this :
https://studentforums.biz/pastpapers/edexcel-unit-6b-(6ch08)-practicals/
GG :)
Post by: Malak on May 26, 2011, 01:50:39 pm
Post by: **RoRo** on May 26, 2011, 03:23:11 pm
What is the explanation of graphite being malleable?
The intermolecular force of attraction between the layers of atoms, the Van der Walls force of attraction is a relatively weak force that can be easily broken and therefore the individual layers can slide over each other making graphite malleable.
Post by: NidZ- Hero on May 26, 2011, 03:25:16 pm
Post by: elemis on May 26, 2011, 03:32:35 pm
why do we use acidifed potassium dichromate to oxidise ethanol?
The Hydrogen ions from the acid aid the change of oxidation state of the Chromium which in turn enables oxidation.
Post by: NidZ- Hero on May 26, 2011, 03:42:07 pm
The Hydrogen ions from the acid aid the change of oxidation state of the Chromium which in turn enables oxidation.rgght the hydrogen ion in the acid react with the metal ion( POTASSIUM )in potassium dichromate n den Chromium ions are formed
Post by: NidZ- Hero on May 26, 2011, 04:06:46 pm
For tollens reagents or the Benedict solution ?
Post by: Malak on May 26, 2011, 04:35:14 pm
we dont have to write half equation to show the colour changes in test for aldehyde and ketonesNah i dont think so...Just know the colour change
For tollens reagents or the Benedict solution ?
Post by: Malak on May 26, 2011, 04:46:09 pm
Post by: ~ Miss Relina ~ on May 26, 2011, 06:08:33 pm
Nah i dont think so...Just know the colour changecan u say the color change 8)
Post by: Aadeez || Zafar on May 26, 2011, 06:10:49 pm
can u say the color change 8)tollens reagant reacts with aldehyde to give silver mirrosing and benedicts reagant react with aldehyde to give red ppt. while ketones do not react with tollens nor with benedicts
Post by: NidZ- Hero on May 26, 2011, 06:21:28 pm
Post by: NidZ- Hero on May 26, 2011, 06:24:56 pm
For which organic molecules do we need to know the shapes and angles??
WOOT according to my memory you should know the shape Not the angles of organic ONLY
Post by: The Golden Girl =D on May 26, 2011, 07:12:27 pm
Neucleophile
Electrophile
Free radical
Thanks :)
Post by: NidZ- Hero on May 26, 2011, 07:19:53 pm
I need Definition for ;
Neucleophile
Electrophile
Free radical
Thanks :)
Neucleophile :are ions or molecules with a lone pair of electrons that attack positive ions or positive centers in the molecule
Electrophiles :are reactive ions and molecules which attack negative ions or the negative centers in the molecules
Free radicals :are highly reactive single atoms, or a group of atoms with unpaired electrons
Post by: The Golden Girl =D on May 26, 2011, 07:29:34 pm
Post by: NidZ- Hero on May 26, 2011, 09:00:59 pm
Don't neucelophiles form dative covalent bonds too ?
No it doesnt
Post by: EMO123 on May 27, 2011, 04:19:58 am
thanxx dear +rep
Neucleophile :are ions or molecules with a lone pair of electrons that attack positive ions or positive centers in the molecule
Electrophiles :are reactive ions and molecules which attack negative ions or the negative centers in the molecules
Free radicals :are highly reactive single atoms, or a group of atoms with unpaired electrons
Post by: Malak on May 27, 2011, 09:39:35 am
(http://www.layoutlocator.com/graphics/dldimg/4d6cb9edb49bf503fc575f65062d6aa1_ac6aaa149266191e93099a75f3b5f4b7.gif)
Post by: NidZ- Hero on May 27, 2011, 10:17:11 am
Hope it all goes well
Inshaallah
Post by: NidZ- Hero on May 27, 2011, 10:17:41 am
Good luck everyone today :D
(http://www.layoutlocator.com/graphics/dldimg/4d6cb9edb49bf503fc575f65062d6aa1_ac6aaa149266191e93099a75f3b5f4b7.gif)
Angel Chill its goonna be cool :0
Post by: Malak on May 27, 2011, 10:23:51 am
Angel Chill its goonna be cool :0Lol..Yeah
That was just a goodluck wish ;)
Post by: angelofhope on May 28, 2011, 11:24:04 am
No it doesnt
really? umm.. isnt water a nucleophile? it forms dative covalent bonds where the transition metal complexes are formed right? im not sure ???
Post by: elemis on May 28, 2011, 11:31:15 am
really? umm.. isnt water a nucleophile? it forms dative covalent bonds where the transition metal complexes are formed right? im not sure ???
Yes, you are correct. Nucleophiles do, at times, form dative covalent bonds with other reactants.
Post by: NidZ- Hero on May 28, 2011, 12:06:30 pm
Post by: Ghayth on May 28, 2011, 12:55:16 pm
State and explain wether the following reaction can occur.
3Fe2+ ----> Fe + 2Fe3+
Given :
Fe3+ + e- ---> Fe2+ +0.77v
Fe2+ + 2e- ----> Fe -0.44v
Can someone please help ? My teacher seemed to flip the signs on some of the E values and I can't seem to figure out why.
Thanks :)
Post by: shwe on May 28, 2011, 04:21:48 pm
If you add two E values, it would give you the "positive" values. As you may know, the reaction is feasible if the E value is positive.
And you don't have to multiply each E values or change the sign since E is not affected with coefficient of equation.
I hope it helps.
Post by: Ghayth on May 28, 2011, 04:26:44 pm
E of cell= -0.44-0.77= - 1.21V , rxn is not feasible.
I'm confused :-\
Post by: shwe on May 28, 2011, 04:39:09 pm
ya, the sign should be reverse, making it negative, since the question is from Fe2+ to 3+ but the equation is from Fe3+ to 2+ .
tht's not feasible.
sorry mate, for not reading the question well enough.
Post by: Ghayth on May 28, 2011, 04:39:50 pm
Post by: angelofhope on June 01, 2011, 06:34:23 am
what do u observe when a piece of copper metal is added to Cr3+(aq) solution? explain ur answer by using the electrode potentials given below.
Cr3+(aq) + 3e- -------> Cr(s) E cell value = -0.77 V
Cu2+ + 2e- -------> Cu(s) Ecell value = +0.34 V
Thanks =D
Post by: wakemeup on June 02, 2011, 11:17:25 am
hey.. can anyone help me with this question?
what do u observe when a piece of copper metal is added to Cr3+(aq) solution? explain ur answer by using the electrode potentials given below.
Cr3+(aq) + 3e- -------> Cr(s) E cell value = -0.77 V
Cu2+ + 2e- -------> Cu(s) Ecell value = +0.34 V
Thanks =D
I'm not 100% sure but I think that nothing should happen. Chromium has the tendency to lose electrons according to the E cell value and the solution already has Cr3+ ions in it. Copper ions have the tendency to gain electrons as shown by the standard potential and there are no Cu2+ ions in the solid copper metal. Therefore there is no initiative for either element to lose or gain electrons and no reaction should take place.
Again, I'm not completely sure if what I'm saying is right so it would be great if someone could confirm or correct my answer.
Post by: angelofhope on June 02, 2011, 07:26:38 pm
Post by: Vampire-Love4ever on June 03, 2011, 09:13:46 am
Why does addition of water make the reaction between Ammonium chloride and Sodium nitrate (lll) become spontaneous?
Post by: wakemeup on June 03, 2011, 09:52:29 am
A2:
Why does addition of water make the reaction between Ammonium chloride and Sodium nitrate (lll) become spontaneous?
First we have to ask ourselves that what does spontaneous mean? It means the tendency of the reaction 'to go'. In other words, an increase in entropy and therefore, the number of ways of distributing energy. When we introduce a liquid such as water between 2 solids, the disorder and randomness of the energy distributed when the reaction takes place also increases. So when the reaction does happen, energy can be more easily distributed among the products and therefore, the reaction is spontaneous.
Post by: Vampire-Love4ever on June 03, 2011, 10:02:31 am
Thank you! :D
First we have to ask ourselves that what does spontaneous mean? It means the tendency of the reaction 'to go'. In other words, an increase in entropy and therefore, the number of ways of distributing energy. When we introduce a liquid such as water between 2 solids, the disorder and randomness of the energy distributed when the reaction takes place also increases. So when the reaction does happen, energy can be more easily distributed among the products and therefore, the reaction is spontaneous.
My brain doesn't seem to working a.t.m. :P
Post by: sharleen07 on June 03, 2011, 07:16:47 pm
I have another question..what is the peak area ratio for 2-methylpropanal?
Post by: Romeesa-Chan on June 04, 2011, 09:11:18 am
Could some one please explain it?
Post by: Romeesa-Chan on June 04, 2011, 11:08:20 am
Please explain how to do that question.
Post by: wakemeup on June 04, 2011, 12:18:39 pm
Unit 6B, Sample Paper, Q3f.
Could some one please explain it?
As the solution is diluted more than 250 cm3, the amount of Fe2+ ions in each portion of 25cm3 decreases which means that the volume of Potassium manganate required for each titration is less as well.
Unit 6B, Jan 2011, Q1d.
Please explain how to do that question.
We know that the potassium ions are present and that Chromium ions are present as well. We know that the only anion is the sulphate ion so the only possibility is that both cations form a salt with the anion and therefore K2SO4.Cr2(SO4)3 is the answer.
Post by: Romeesa-Chan on June 04, 2011, 12:44:23 pm
As the solution is diluted more than 250 cm3, the amount of Fe2+ ions in each portion of 25cm3 decreases which means that the volume of Potassium manganate required for each titration is less as well.
We know that the potassium ions are present and that Chromium ions are present as well. We know that the only anion is the sulphate ion so the only possibility is that both cations form a salt with the anion and therefore K2SO4.Cr2(SO4)3 is the answer.
But, how do we make the formula of the complex? :-\
Post by: wakemeup on June 04, 2011, 12:56:01 pm
But, how do we make the formula of the complex? :-\
That's a rather simple technique. When two ions combine, charges are interchanged into the number of the atoms present . Like in this question, Potassium ion has a +1 charge, so there is one sulphate. The sulphate ion has a -2 charge, so there are 2 Potassiums in the formula. Similarly, Chromium ion has a +3 charge, so there are 3 sulphates and 2 Chromiums in the formula.
Hope that helps
Post by: Romeesa-Chan on June 04, 2011, 01:00:41 pm
That's a rather simple technique. When two ions combine, charges are interchanged into the number of the atoms present . Like in this question, Potassium ion has a +1 charge, so there is one sulphate. The sulphate ion has a -2 charge, so there are 2 Potassiums in the formula. Similarly, Chromium ion has a +3 charge, so there are 3 sulphates and 2 Chromiums in the formula.
Hope that helps
THANKS ALOT! Your explanation was great! Thanks sooooo much!!!!!!!!!!!!!
Post by: wakemeup on June 04, 2011, 01:13:57 pm
Post by: Romeesa-Chan on June 04, 2011, 03:59:41 pm
Please explain it. =)
Post by: elemis on June 04, 2011, 04:03:47 pm
Jan 2011, Q 2 a ii & iii
Please explain it. =)
Could you link the paper or attach it , please.
Post by: Romeesa-Chan on June 04, 2011, 04:08:57 pm
Could you link the paper or attach it , please.
Post by: Romeesa-Chan on June 04, 2011, 07:31:13 pm
Post by: guMnam on June 05, 2011, 10:05:55 pm
Post by: Malak on June 05, 2011, 10:08:30 pm
Post by: Romeesa-Chan on June 05, 2011, 10:08:57 pm
wat is a disproportionation reaction ???
Oxidation-reduction reaction in which the same element is both oxidized and reduced.
Post by: studz on June 06, 2011, 05:41:29 pm
i'd really +rep that person! lol
also could anyone tell me what all do we need to study for unit 6 precisely? thanks
Post by: High-R on June 06, 2011, 07:02:43 pm
is a good site might help!
unit6- just practice the pastpapers and review exercises in the text books!
:D
Post by: Amelia on June 06, 2011, 07:03:38 pm
could anyone summarize and post reactions of benzene phenol diazonium and azo dye??? ??? ??? :-\
i'd really +rep that person! lol
also could anyone tell me what all do we need to study for unit 6 precisely? thanks
Reactions of Diazonium Salts (http://www.chemguide.co.uk/organicprops/aniline/propsdiazo.html), Benzene (http://www.chemguide.co.uk/mechanisms/elsubmenu.html) and Phenol (http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch24reactionphenols.html)
Post by: studz on June 06, 2011, 07:46:34 pm
Reactions of Diazonium Salts (http://www.chemguide.co.uk/organicprops/aniline/propsdiazo.html), Benzene (http://www.chemguide.co.uk/mechanisms/elsubmenu.html) and Phenol (http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch24reactionphenols.html)
u sure about this ??? ??? because i am having a hard time studying unit 5's organic chem for unit 6
! its so hard! :-\ :'(
i thought its all about simple identification tests for carbonyl groups and all..the basic stuff :/
Post by: Amelia on June 06, 2011, 07:55:30 pm
u sure about this ??? ??? because i am having a hard time studying unit 5's organic chem for unit 6
! its so hard! :-\ :'(
i thought its all about simple identification tests for carbonyl groups and all..the basic stuff :/
Unit 6 as in Practicals? I thought different. Well, then you dont have to read those. Just revise your practice papers. ;)
I haven't done Edexcel so I wont be of much help in the practical part. :(
Post by: studz on June 06, 2011, 08:06:03 pm
oh ok u do CIE..well np :)
Post by: Amelia on June 06, 2011, 08:08:46 pm
its alternative to practical actually..argh i have no idea :-\ ???
oh ok u do CIE..well np :)
You are just nervous. It's not a good thing, you know ::) :P Just relax and revise whatever you have done already in Unit 6. That's all.
Used to do* ;)
Post by: Assi1993 on June 06, 2011, 08:15:09 pm
Post by: studz on June 06, 2011, 08:16:52 pm
besides we only have 3 papers to practice so thats why
oh great we have a senior here :P
yes assi that is what i am doing..organic reactions are so yuk! :P
Post by: ibuprofen500 on June 06, 2011, 08:47:07 pm
Post by: Romeesa-Chan on June 06, 2011, 08:52:56 pm
lol yeah i am kinda nervous because there is alot to do maybe
besides we only have 3 papers to practice so thats why
oh great we have a senior here :P
yes assi that is what i am doing..organic reactions are so yuk! :P
Ditto. The last chapter in the textbook is just EW.
Post by: Malak on June 06, 2011, 08:55:34 pm
does anyone have notes on preparation of aspirin or paracetamol ? which ever it is in the courseI dont know much about the A2 syllabus as I am doing AS, but I found this, Dont know how much it is relevant..
File is attached
Post by: studz on June 06, 2011, 08:56:10 pm
Ditto. The last chapter in the textbook is just EW.
ikr! the worst chapter ever :P
Post by: Romeesa-Chan on June 06, 2011, 08:59:22 pm
ikr! the worst chapter ever :P
Not looking forward to tomorrow's exam.
=.=
Post by: ibuprofen500 on June 06, 2011, 08:59:48 pm
Post by: Malak on June 06, 2011, 09:02:50 pm
I have that, but its aspirin and the reagents used are totally other than those in my books ( which also mostly say about paracetamol) ... i wonder why is there so many variation and which one are we suppose to do?I suggest check the specification, and learn the one which the book mentions..
Post by: studz on June 06, 2011, 09:11:16 pm
Not looking forward to tomorrow's exam.
=.=
seriously!! just wanna escape somehow! and not fail too lol! wish there was a way out like that *-)
Post by: Romeesa-Chan on June 06, 2011, 09:25:29 pm
seriously!! just wanna escape somehow! and not fail too lol! wish there was a way out like that *-)
Haha. Lol. Let's keep wishing. For now. . . just revise everything and do your best tomorrow!
All the best! ;)
Post by: studz on June 06, 2011, 10:05:47 pm
Haha. Lol. Let's keep wishing. For now. . . just revise everything and do your best tomorrow!
All the best! ;)
yeah..sigh!
all the very best to u too ::)
Post by: Assi1993 on June 06, 2011, 10:13:50 pm
anyway...
good luck guys...........
Post by: Romeesa-Chan on June 06, 2011, 10:16:17 pm
i feel tensed..they should have given a gap between phy 6 n chem 6...
anyway...
good luck guys...........
I know, right?
I already feel drained thanks to Physics. =/
I will be a living dead body tomorrow. :P [if that makes any sense] :P
Ahhh. . . there are so many tests to remember! :|
Good luck! ;)
Post by: studz on June 06, 2011, 10:30:54 pm
i feel tensed..they should have given a gap between phy 6 n chem 6...
anyway...
good luck guys...........
yeah they should have but anyway forget it now
i had more high (impossible) hopes such as escaping the paper without the fear of failing :P
i already have a pretty messed up schedule up ahead :-\
ill finish in late june! >:(
Post by: Malak on June 06, 2011, 11:39:47 pm
M sure all the suffering will be worth it in the end :)
Post by: Romeesa-Chan on June 06, 2011, 11:42:01 pm
Question: for the flame test, do we dip the nichrome wire into dilute or concentrated HCl?
Post by: Assi1993 on June 07, 2011, 12:03:18 am
Post by: Malak on June 07, 2011, 12:04:58 am
I guess, those taking Edexcel Physics for A2 finishes last. ^^Concentrated
Question: for the flame test, do we dip the nichrome wire into dilute or concentrated HCl?
Post by: Romeesa-Chan on June 07, 2011, 12:30:14 am
Concentrated
Thank you! God bless. =]
Post by: Assi1993 on June 07, 2011, 03:41:46 am
Post by: NotAbod on June 07, 2011, 03:46:22 am
Good Luck.
Post by: Assi1993 on June 09, 2011, 12:15:42 am
Okay, First off, revise everything! and solve if you still have enough time, but if only 3-8 hours are left, then keep revising, and don't waste your time in solving. what you can't memorise, write it, till you learn it. ;D :)
Good Luck.
:) thanks ..i will not forget this peice of advice ;)
Post by: Romeesa-Chan on June 12, 2011, 02:59:51 pm
Q10 and Q12b
http://www.edexcel.com/migrationdocuments/GCE%20New%20GCE/sam-gce-chemistry.pdf
Post by: Romeesa-Chan on June 12, 2011, 03:44:06 pm
Q3, Q18 and Q20
Post by: Amelia on June 12, 2011, 03:46:53 pm
*Chem 4 [sample paper] doubts:
Q10 and Q12b
http://www.edexcel.com/migrationdocuments/GCE%20New%20GCE/sam-gce-chemistry.pdf
I hope I've got the right questions. :P
Q10) Titration of strong base and strong acid.
(a) What was the pH when 24.95 cm3 of 1.00 mol dm–3 NaOH(aq) had been added to 25 cm3 of 1.00 mol dm–3 HCl(aq)?
Ans is A. The volume of NaOH added is less then the volume of acid. So, the solution is still acidic. The pH only falls very slightly until its quite near the "equivalence point".
(b) What was the pH when 25.05 cm3 of 1.00 mol dm–3 NaOH(aq) had been added to 25 cm3 of 1.00 mol dm–3 HCl(aq)?
Ans is D. The volume of alkali is here is more then the volume of acid. More OH ions in the solution, so higher pH.
(c) Which one of the following indicators would be MOST suitable to use to determine the end point of this titration?
pH range
A methyl violet 0-1.6
B universal Indicator 3-11
C thymolphthalein 8.3-10.6
D alizarin yellow R 10.1-13.0
C. As the pH range shows this indicator is a weak acid, it can easily change color when the hydroxide ions are added and the end point is reached.
Post by: Romeesa-Chan on June 12, 2011, 03:53:43 pm
I hope I've got the right questions. :P
Q10) Titration of strong base and strong acid.
(a) What was the pH when 24.95 cm3 of 1.00 mol dm–3 NaOH(aq) had been added to 25 cm3 of 1.00 mol dm–3 HCl(aq)?
Ans is A. The volume of NaOH added is less then the volume of acid. So, the solution is still acidic. The pH only falls very slightly until its quite near the "equivalence point".
(b) What was the pH when 25.05 cm3 of 1.00 mol dm–3 NaOH(aq) had been added to 25 cm3 of 1.00 mol dm–3 HCl(aq)?
Ans is D. The volume of alkali is here is more then the volume of acid. More OH ions in the solution, so higher pH.
(c) Which one of the following indicators would be MOST suitable to use to determine the end point of this titration?
pH range
A methyl violet 0-1.6
B universal Indicator 3-11
C thymolphthalein 8.3-10.6
D alizarin yellow R 10.1-13.0
C. As the pH range shows this indicator is a weak acid, it can easily change color when the hydroxide ions are added and the end point is reached.
JazakAllah khair! :D
Post by: EMO123 on June 12, 2011, 03:56:01 pm
JazakAllah khair! :Dmeans what
Post by: Amelia on June 12, 2011, 03:57:38 pm
*Chem 4 Jan 2010 doubts:
Q3, Q18 and Q20
Q3 - Ans. is B. About phenolphthalein - the weak acid is colourless and its ion is bright pink. Adding extra hydrogen ions shifts the position of equilibrium to the left, and turns the indicator colourless. Adding hydroxide ions removes the hydrogen ions from the equilibrium which tips to the right to replace them - turning the indicator pink.
Post by: Romeesa-Chan on June 12, 2011, 04:01:09 pm
Q19 ai & b
Post by: Romeesa-Chan on June 12, 2011, 04:04:13 pm
means what
Phrase that people use to thank others. It literally means 'May Allah grant you goodness'.
:)
Post by: EMO123 on June 12, 2011, 04:05:33 pm
Phrase that people use to thank others. It literally means 'May Allah grant you goodness'.wow only a short phrase with a long meaning
:)
Post by: Amelia on June 12, 2011, 04:10:09 pm
*Chem 4 Jan 2010 doubts:
Q3, Q18 and Q20
Q 18 - Ans. is A. Draw both the molecules first.. then, delete H2O from both sides. ::) (I'm sure you wont get it, but try :P)
Q 20 - Ans. is C. The disassociation is endothermic. And Kw increases as the temperature increases, so more H+ at higher temperature.
Post by: Romeesa-Chan on June 12, 2011, 04:14:18 pm
Q 18 - Ans. is A. Draw both the molecules first.. then, delete H2O from both sides. ::) (I'm sure you wont get it, but try :P)
=.= I thought of A too! But, according to MS it is C. >,<
Post by: Amelia on June 12, 2011, 04:20:26 pm
=.= I thought of A too! But, according to MS it is C. >,<
LOL! I'm sorry. Yes, it must be C, because they have asked for just one repeat unit. This unit will repeat itself to form the polyster.
'A' is right, but it's one unit and half. ::)
Post by: Amelia on June 12, 2011, 04:30:04 pm
*Chem 4 June 2010 doubts:
Q19 ai & b
Q 19 ai) - You have tried doing it, yeah?
Kp= P CH3COOH/ P CH3OH X P CO
Post by: Romeesa-Chan on June 12, 2011, 04:32:23 pm
Q 19 ai) - You have tried doing it, yeah?
Kp= P CH3COOH/ P CH3OH X P CO
Yes, I have tried! :D
But, I didn't get how to do it! :S
Plus, That Q18 . . . I still don't get why can't the answer be A! :/
Post by: Amelia on June 12, 2011, 04:40:45 pm
Yes, I have tried! :D
But, I didn't get how to do it! :S
Now you do, yes? Partial pressure of the products divided by the partial pressure of the reactants. Don't forget the units. Here it will be atm-1
As for the B part, try doing it yourself first.. Find the no. of moles at equilibrium. (93.6% of 50 moles gives the no. of moles for CH3COOH), then find the mole fraction due to each of the molecules. Then the partial pressure, and Kp.
Quote
Plus, That Q18 . . . I still don't get why can't the answer be A! :/
A is the result of ethane 1,2-diol + benzene-1,4-dicarboxylic acid + (another) ethane-1,2-diol...while,
C is just ethane 1,2-diol + benzene-1,4-carboxylic acid - this forms the repeat unit.
Do you get it, now?
Post by: Romeesa-Chan on June 12, 2011, 04:54:46 pm
Now you do, yes? Partial pressure of the products divided by the partial pressure of the reactants. Don't forget the units. Here it will be atm-1
A is the result of ethane 1,2-diol + benzene-1,4-dicarboxylic acid + (another) ethane-1,2-diol...while,
C is just ethane 1,2-diol + benzene-1,4-carboxylic acid - this forms the repeat unit.
Do you get it, now?
Yes! Thanks muchos! :D
Post by: Amelia on June 12, 2011, 04:56:50 pm
Yes! Thanks muchos! :D
Cool! ;)
Post by: Romeesa-Chan on June 12, 2011, 05:00:48 pm
JazakAllah khair! :D
Post by: hkhkhk119 on June 14, 2011, 09:16:15 am
Post by: studz on June 14, 2011, 10:52:12 am
Post by: studz on June 14, 2011, 11:03:24 am
Post by: Romeesa-Chan on June 14, 2011, 11:13:37 am
I wanna ask what is the difference between High Ea and the reaction not spontaneous(delta S =-ve)?
@hkhkhk119- Reaction is not spontaneous when delta S total is negative.
High activation energy indicates reactants are kinetically inert/kinetically stable.
@studz- I was gonna link you right now! Haha! Good you got it! :)
Post by: Romeesa-Chan on June 14, 2011, 11:47:27 am
I hope I've got the right questions. :P
Q10) Titration of strong base and strong acid.
(a) What was the pH when 24.95 cm3 of 1.00 mol dm–3 NaOH(aq) had been added to 25 cm3 of 1.00 mol dm–3 HCl(aq)?
Ans is A. The volume of NaOH added is less then the volume of acid. So, the solution is still acidic. The pH only falls very slightly until its quite near the "equivalence point".
(b) What was the pH when 25.05 cm3 of 1.00 mol dm–3 NaOH(aq) had been added to 25 cm3 of 1.00 mol dm–3 HCl(aq)?
Ans is D. The volume of alkali is here is more then the volume of acid. More OH ions in the solution, so higher pH.
(c) Which one of the following indicators would be MOST suitable to use to determine the end point of this titration?
pH range
A methyl violet 0-1.6
B universal Indicator 3-11
C thymolphthalein 8.3-10.6
D alizarin yellow R 10.1-13.0
C. As the pH range shows this indicator is a weak acid, it can easily change color when the hydroxide ions are added and the end point is reached.
I am sorry to bother you but I don't understand part (c).
Isn't the titration between a strong acid and a strong base which has a end point range between 4 to 10.
So, isn't it suppose to be B? :S
Post by: studz on June 14, 2011, 12:12:11 pm
Post by: wakemeup on June 14, 2011, 03:07:19 pm
I am sorry to bother you but I don't understand part (c).
Isn't the titration between a strong acid and a strong base which has a end point range between 4 to 10.
So, isn't it suppose to be B? :S
We need an indicator that will change it's colour at or near to the equivalence point. Universal indicator might change it's colour way before the equivalence point, so it is not suitable. The closest range we have to the equivalence point i.e 7 is in thymolphthalein, so it is the most suitable.
Post by: Romeesa-Chan on June 14, 2011, 03:31:01 pm
We need an indicator that will change it's colour at or near to the equivalence point. Universal indicator might change it's colour way before the equivalence point, so it is not suitable. The closest range we have to the equivalence point i.e 7 is in thymolphthalein, so it is the most suitable.I got it and was gonna delete my post. Thanks muchos! ;)
Post by: Romeesa-Chan on June 14, 2011, 03:47:07 pm
Please urgent!
Post by: Assi1993 on June 14, 2011, 09:27:09 pm
Post by: guMnam on June 14, 2011, 10:18:17 pm
can some1 tell me that how is D the answer?change is 3 (tripled) and the sum of orders is 1 + 2 = 3
therefore
31+2=27
Post by: Romeesa-Chan on June 14, 2011, 10:29:03 pm
can some1 tell me that how is D the answer?Hope image is clear. :)
Post by: Assi1993 on June 14, 2011, 10:40:02 pm
Post by: Romeesa-Chan on June 14, 2011, 10:49:12 pm
thanku u both <3 :) !
Welcome!
Can you PLEASE help me with Q18ciii&iv from the sample paper?!
Post by: Assi1993 on June 15, 2011, 12:02:02 am
Post by: Romeesa-Chan on June 15, 2011, 12:19:22 am
i dont know either :( !! @ rumeesa....
=(
I guess no one knows! I tried asking everyone! :(
Post by: Romeesa-Chan on June 15, 2011, 01:17:59 am
Post by: HUSH1994 on June 15, 2011, 04:30:38 am
amount of hydrogen produced is less than if there were excess HCl. That's due to the fact that the HCl is now the limiting reactant and when it's all used up,the reaction stops, even if there is still unreacted magnesium.
About the question in the attachment,can please post the link for the past paper so i check it :)
Post by: Romeesa-Chan on June 15, 2011, 06:19:40 am
The concentration of the acid would not affect the amount of H2 gas produced.If there is excess hydrochloric acid, the reaction goes until all the magnesiumis used up and then stops. The reaction might be more vigorous if the acid is more concentrated, but when one or the other of the reactants is used up, the reaction will stop.If the acid were so dilute that the HCl is used up before all the magnesium, the
amount of hydrogen produced is less than if there were excess HCl. That's due to the fact that the HCl is now the limiting reactant and when it's all used up,the reaction stops, even if there is still unreacted magnesium.
About the question in the attachment,can please post the link for the past paper so i check it :)
Thank youuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu, senpai! :D
http://www.edexcel.com/migrationdocuments/GCE%20New%20GCE/sam-gce-chemistry.pdf
It's Unit 4- hope you find it! ;)
Post by: HUSH1994 on June 15, 2011, 06:34:44 am
Welcome!These parts?
Can you PLEASE help me with Q18ciii&iv from the sample paper?!
Post by: Romeesa-Chan on June 15, 2011, 07:32:35 am
These parts?
Hai.
Post by: HUSH1994 on June 15, 2011, 08:19:39 am
Post by: Romeesa-Chan on June 15, 2011, 08:24:09 am
sorry but both parts look quite complicated,i never studies anything like that before(not in the AS),its looks quite challenging :O, anyway can you please link it to its mark scheme,i might get something from there ;)
It's alright if you can't. I appreciate that you even tried.
I know. The thing is, I've not seen such a question EVER either. Part c iii- I don't understand the mass calculation.
We used moles of Mg initially but then for temperature change, we used HCl. I don't get that.
Part civ I don't understand the time thingy.
The mark scheme is at the end of the link I gave previously. ;)
Post by: HUSH1994 on June 15, 2011, 08:34:16 am
ill take a look at the mark scheme and tell you if i got anything ;)
Post by: Romeesa-Chan on June 15, 2011, 08:41:20 am
in part iii) the mass is 100,you have to use the mass\volume in cm^3 of the liquid\solution reacting.
ill take a look at the mark scheme and tell you if i got anything ;)
Mass taken is 20g from HCl which was 20cm^-1.
Post by: wakemeup on June 15, 2011, 08:56:42 am
Part c iii- I don't understand the mass calculation.
We used moles of Mg initially but then for temperature change, we used HCl. I don't get that.
Part civ I don't understand the time thingy.
I'm kind of confused here myself but I'm guessing we're taking the moles of magnesium in the calculation because the delta H is referring to one mole for the compounds and elements that are already one mole in the equation. So HCl can disregarded in the calculation. Again, I'm not 100% sure here.
Part iv is much easier. Take the time for 56C from the previous table and subtract 2 from it and then take the time for 10C and add 2 to it. Find theur inverse and then the ln of the inverse values. Now you can draw the graph and as we're considering ln1/T proportional to lnk, your gradient will be -Ea/R, according to y= mx+c so now you can find the new value of the activation energy.
Hope that helps.
Post by: Romeesa-Chan on June 15, 2011, 09:01:23 am
I'm kind of confused here myself but I'm guessing we're taking the moles of magnesium in the calculation because the delta H is referring to one mole for the compounds and elements that are already one mole in the equation. So HCl can disregarded in the calculation. Again, I'm not 100% sure here.
Part iv is much easier. Take the time for 56C from the previous table and subtract 2 from it and then take the time for 10C and add 2 to it. Find theur inverse and then the ln of the inverse values. Now you can draw the graph and as we're considering ln1/T proportional to lnk, your gradient will be -Ea/R, according to y= mx+c so now you can find the new value of the activation energy.
Hope that helps.
For part vi, why do we add 2 for one value and minus 2 from the other?
That's what confused me.
Post by: wakemeup on June 15, 2011, 09:04:07 am
For part vi, why do we add 2 for one value and minus 2 from the other?
That's what confused me.
They said in the question that there could be an error of 2 seconds and then told us to find the shortest time for one of the values (ie -2) and the longest time for the other value (ie +2)
Post by: samriddh on June 18, 2011, 04:43:03 pm
and ya do we have notes on organic chemistry esp chiral molecules and "hydrocarbons: fuels"
thank you for the help in advance!!
Post by: iluvme on June 18, 2011, 04:45:37 pm
Post by: Ghayth on June 18, 2011, 04:52:04 pm
You have 2 reactions ,
Cu2+ + e- -----> Cu+ +0.15v
I2 + 2e- -----> 2I- +0.53v
Q) Calculate E of cell for the reaction.
What is wrong with what I am doing ?
I see that 0.15<0.53 so I deduce that Cu+ will be oxidised at the anode and I2 will be reduced at the cathode.
E of cell= Reduction - oxidation
E of cell= 0.53 - 0.15 = 0.39V
My notebook says that the E of the cell is - 0.39V :s
Post by: Romeesa-Chan on June 18, 2011, 09:50:59 pm
This E of cell stuff is really confusing ..
You have 2 reactions ,
Cu2+ + e- -----> Cu+ +0.15v
I2 + 2e- -----> 2I- +0.53v
Q) Calculate E of cell for the reaction.
What is wrong with what I am doing ?
I see that 0.15<0.53 so I deduce that Cu+ will be oxidised at the anode and I2 will be reduced at the cathode.
E of cell= Reduction - oxidation
E of cell= 0.53 - 0.15 = 0.39V
My notebook says that the E of the cell is - 0.39V :s
It gotta be +0.38V.
*Always make the more negative value the LHS (left hand side).
E cell= E (RHS) - E (LHS)
By the way, which textbook?
Post by: Ghayth on June 19, 2011, 05:10:03 am
Its not my text book , just my teacher's notes so I guess it was a mistake but thanks
Post by: Romeesa-Chan on June 19, 2011, 05:33:00 am
I know right ? ???It happens. Must've been a mistake! :)
Its not my text book , just my teacher's notes so I guess it was a mistake but thanks
Good luck! (=
Post by: abuelzouz on June 22, 2011, 08:12:32 pm
Post by: Romeesa-Chan on June 23, 2011, 04:44:00 am
hey people...how 's unit 5?
It's fine. Just need to remember loads and practice the questions. It better be better than Unit 4. >:(
Post by: abuelzouz on June 23, 2011, 08:28:05 am
It's fine. Just need to remember loads and practice the questions. It better be better than Unit 4. >:(
i thought unit 4 was good :)
nobody has doubts? lets share some stuyff
Post by: Romeesa-Chan on June 23, 2011, 08:32:11 am
i thought unit 4 was good :)
nobody has doubts? lets share some stuyff
I might fail that paper. ::)
Not at the moment. I might be posting later in the evening.
How's revision going?
Post by: guMnam on June 23, 2011, 09:47:50 am
Post by: guMnam on June 23, 2011, 09:49:32 am
Post by: abuelzouz on June 23, 2011, 09:53:46 am
Post by: Romeesa-Chan on June 23, 2011, 09:55:04 am
okay.. how does a benzene ring get deactivated ? i mean what groups or what ever deactivatesa benzene ring.. can somebody give me examples ?
That is because one the lone pair of electrons from the oxygen atom on the -OH group interacts with delocalised electrons.
Yes, learn the transition metal test- when we add NaOH and NH3 (+in excess).
Post by: guMnam on June 23, 2011, 11:05:36 am
Post by: Assi1993 on June 23, 2011, 11:43:16 am
Post by: abuelzouz on June 23, 2011, 01:03:15 pm
when co-ordination no of complex is 2
shape is linear
orbitals to be filled sp
when co-ordination no of complex is 4
shape is either square planar
orbitals to be filled dsp^2
or tetrahedral
orbitals to be filled sp^3
when co-ordination no of complex is 6
shape is either octahedral
orbitals to be filled d^2 sp^3
Post by: Romeesa-Chan on June 23, 2011, 03:27:14 pm
^ so wat do u think happens wen it is deactivated by -NH2 group in phenylamine
^Deactivated by NH2? I am sorry, I don't get it. :/
Post by: Assi1993 on June 23, 2011, 03:47:49 pm
^Deactivated by NH2? I am sorry, I don't get it. :/
@Assi1993- NH4+ acts a ligand because it has lone pair of electron present on the Nitrogen atom which forms a covalent bond with the transition metal ion.
noo..why it does NOT form ligandS??
Post by: Romeesa-Chan on June 23, 2011, 03:55:17 pm
noo..why it does NOT form ligandS??
WOW. Sorry read it wrong there. :-[
Complexes are generally formed by donation of a pair of electrons from the ligand to metal; as NH3 with a lone pair on nitrogen can form complex with copper by donating the pair to metal ion. In case of NH4+ the lone pair is not available, so it will not form the complex.
Post by: Assi1993 on June 23, 2011, 04:41:30 pm
WOW. Sorry read it wrong there. :-[
Complexes are generally formed by donation of a pair of electrons from the ligand to metal; as NH3 with a lone pair on nitrogen can form complex with copper by donating the pair to metal ion. In case of NH4+ the lone pair is not available, so it will not form the complex.
thanks sis :) By the way hows prep?
Post by: Romeesa-Chan on June 23, 2011, 04:44:36 pm
thanks sis :) By the way hows prep?
Welcome, sis! <3
Hmmmm, not so great. I am FREAKED OUT. I have to revise Transition Metals properly.
I am gonna do the papers now and let's see.
How's your prep?? (:
Post by: Assi1993 on June 23, 2011, 04:51:04 pm
and im freaking out too...!!
good luck!!!!!!!! :)
Post by: Romeesa-Chan on June 23, 2011, 04:53:42 pm
ahan..im doing papers..
and im freaking out too...!!
good luck!!!!!!!! :)
Good luck, dear! <3
Do your best! :D
By the way, how was Unit 4?
Post by: abuelzouz on June 23, 2011, 06:32:10 pm
i just heard of something called CGP revision guide.. Does anybody Have it ? A link or something? They say its pretty good... ?
Please!
Post by: EMO123 on June 23, 2011, 06:35:34 pm
anybody From Here can you plzz do this the post of mine it is from CIE
if paper needed then ask that for
Post by: wakemeup on June 23, 2011, 06:39:18 pm
Guys why doesnt NH4+ act as ligands in formation of complexes?
Simple rule to remember. Only anions and neutral molecules can form ligands.
Post by: EMO123 on June 23, 2011, 06:41:19 pm
Post by: wakemeup on June 23, 2011, 06:45:05 pm
Well Best of luck Edexcel Guys for your paper on Monday of Chemistry
Actually, chemistry's tomorrow, but thanks regardless.
Post by: EMO123 on June 23, 2011, 06:47:09 pm
my bad
Actually, chemistry's tomorrow, but thanks regardless.
best lucks for tomorrow
Post by: Romeesa-Chan on June 23, 2011, 06:49:54 pm
Simple rule to remember. Only anions and neutral molecules can form ligands.
Thanks for this, wakemeup! :D
EMO, link me the paper and I will try solving if I can.
Chem is tom and Phy is on Monday. (:
Post by: EMO123 on June 23, 2011, 06:54:19 pm
Thanks for this, wakemeup! :Dhere it is
EMO, link me the paper and I will try solving if I can.
Chem is tom and Phy is on Monday. (:
http://www.xtremepapers.me/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_s07_qp_4.pdf
Post by: Romeesa-Chan on June 23, 2011, 07:00:08 pm
here it is
http://www.xtremepapers.me/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_s07_qp_4.pdf
I will reply in the CIE thread . . .
Post by: EMO123 on June 23, 2011, 07:01:52 pm
I will reply in the CIE thread . . .thanxx and for sure
Post by: abuelzouz on June 23, 2011, 07:20:01 pm
i just heard of something called CGP revision guide.. Does anybody Have it ? A link or something? They say its pretty good... ?
Please
Post by: Romeesa-Chan on June 23, 2011, 07:29:16 pm
hello..
i just heard of something called CGP revision guide.. Does anybody Have it ? A link or something? They say its pretty good... ?
Please
Avoid double posting.
Stick to the Edexcel specification for your own good. I've heard the CGP guide is not that great. Edexcel one is according to the syllabus and covers everything there.
Don't stress yourself the night before exam looking for the guide. :D
Post by: abuelzouz on June 23, 2011, 07:31:47 pm
ok thanks
Post by: Romeesa-Chan on June 23, 2011, 08:29:56 pm
-Q23cii
-Q24c and d. Anyone having a model answer for the d part? Please upload.
Post by: guMnam on June 23, 2011, 09:06:13 pm
Post by: Assi1993 on June 23, 2011, 10:01:33 pm
now lets see if we rape the paper tomorrow or it rapes us:P
Post by: ibuprofen500 on June 24, 2011, 01:16:47 am
Quote
hello..
i just heard of something called CGP revision guide.. Does anybody Have it ? A link or something? They say its pretty good... ?
Please
I have the CGP guides, they are amazing, it is made exactly according to the syllabus, and lots of bits from exam even comes from it, i mean to say the questions are just so similar ( specially chemistry). since my AS level and now my A2 i have been preparing my exams from those books, and they are thin exact to the point and makes you understand so well. I have edexcel guides too but they arnt that good. they are just good for tips on answering questions .
i don't study from edexcel books i just revise and study CGP guides, and so far my grades have been from A's and B's ( and just 2 C's) .
i just commented because someone else said it wasn't good and they weren't right.
CGP revision guides are the key to success and passing in A levels .. if only everyone knew .
Post by: Assi1993 on June 24, 2011, 02:10:22 am
Quote from: abuelzouz on June 23, 2011, 06:20:01 pm
I have the CGP guides, they are amazing, it is made exactly according to the syllabus, and lots of bits from exam even comes from it, i mean to say the questions are just so similar ( specially chemistry). since my AS level and now my A2 i have been preparing my exams from those books, and they are thin exact to the point and makes you understand so well. I have edexcel guides too but they arnt that good. they are just good for tips on answering questions .
i don't study from edexcel books i just revise and study CGP guides, and so far my grades have been from A's and B's ( and just 2 C's) .
i just commented because someone else said it wasn't good and they weren't right.
CGP revision guides are the key to success and passing in A levels .. if only everyone knew .
ohhh thn i wish i had it :|
Post by: Romeesa-Chan on June 24, 2011, 02:12:09 am
The Edexcel revision guide is MUCH better- I got it week before my exam during AS and alhamdullah. . . it was of great help. (:
I am also currently using the Edexcel A2 guide and it's amazing for revision one day before exam. :D
Post by: ibuprofen500 on June 24, 2011, 03:28:18 am
The edexcel guides i don't even bother reading them, i just read the tips part and the examiner comments those are useful since its from edexcel ..
As for me, i dono what i would have done without CGP books .....
anyhow Good luck for the exam, its just in 5 hours ....
Post by: Romeesa-Chan on June 24, 2011, 03:30:38 am
I see, maybe you didn't get the one for edexcel syllabus, or maybe you have different study method.
The edexcel guides i don't even bother reading them, i just read the tips part and the examiner comments those are useful since its from edexcel ..
As for me, i dono what i would have done without CGP books .....
anyhow Good luck for the exam, its just in 5 hours ....
Perhaps that could be the case. (:
The textbook+guide+syllabus is a fine method to study. (for me at least)
Good luck! :D Do your best! :D
Post by: guMnam on June 24, 2011, 04:41:49 am
romeesa U-4 wasnt reallly good for me.........!!!same here .. and i think its gonna happen again.. the baladkaar :P
now lets see if we rape the paper tomorrow or it rapes us:P
Post by: Romeesa-Chan on June 24, 2011, 04:47:15 am
jan 2011 Q 13 why isnt the answer A ??
Haha. I saw this by chance.
Anyways, here goes:
you start with 47g of Phenol, Mr 94.
Moles of phenol = mass / Mr
Moles of phenol = 47/94 = 0.5 moles
You have 85% yield in first step. So 85% of 0.5 = 0.425
You have 80% yield in second step. So 80% of 0.425 = 0.34 moles
This is the moles of aspirin (end product).
Mass = Moles x Mr
Mass = 0.34 x 180 = 61.2g
Therefore, the answer is B and not A.
:D
Post by: Romeesa-Chan on June 24, 2011, 04:49:48 am
same here .. and i think its gonna happen again.. the baladkaar :P
It was HORRIBLE for me. :(
No, this time. . . we will do baladkaar for Chemistry 5. :P
Post by: guMnam on June 24, 2011, 06:36:32 am
Haha. I saw this by chance.thanx but u were late i worked it out already :P
Anyways, here goes:
you start with 47g of Phenol, Mr 94.
Moles of phenol = mass / Mr
Moles of phenol = 47/94 = 0.5 moles
You have 85% yield in first step. So 85% of 0.5 = 0.425
You have 80% yield in second step. So 80% of 0.425 = 0.34 moles
This is the moles of aspirin (end product).
Mass = Moles x Mr
Mass = 0.34 x 180 = 61.2g
Therefore, the answer is B and not A.
:D
and best of luk :)
Post by: Romeesa-Chan on June 24, 2011, 06:39:06 am
thanx but u were late i worked it out already :P
and best of luk :)
Opsie. :P
Good luck! XD
Post by: ibuprofen500 on June 24, 2011, 07:21:12 am
but it was already here answered ..
thanks romeesa chan
Post by: Romeesa-Chan on June 24, 2011, 11:22:51 am
i came here to ask the same question as gunmnam ,,,
but it was already here answered ..
thanks romeesa chan
Welcome! :D
Hope exam went great! :D
Post by: EMO123 on June 24, 2011, 06:48:45 pm
Post by: Romeesa-Chan on June 24, 2011, 06:50:06 pm
Post by: EMO123 on June 24, 2011, 06:51:52 pm
Exam went well, alhamdullah. (:thank god
Post by: **RoRo** on June 25, 2011, 06:51:28 pm
Post by: Romeesa-Chan on June 25, 2011, 06:53:10 pm
I have a question guys, for A2 chemistry, do I need to 're-study' the AS modules as well?
If they are fresh in your mind, it'll be good for you.
Just revise them briefly to brush up your AS memory while doing A2! :D
Post by: EMO123 on June 25, 2011, 06:53:32 pm
I have a question guys, for A2 chemistry, do I need to 're-study' the AS modules as well?well i say one thing prepare for everything so you dont face problem further
Post by: **RoRo** on June 25, 2011, 07:11:24 pm
Another question, I'm going to do A2 privately by myself, what do you recommend: doing it in January or June?
Post by: Romeesa-Chan on June 25, 2011, 10:19:03 pm
Ok, thanks guys. :)
Another question, I'm going to do A2 privately by myself, what do you recommend: doing it in January or June?
How many subjects?
Post by: ~ Miss Relina ~ on June 29, 2011, 06:14:34 pm
Post by: Malak on June 29, 2011, 06:18:49 pm
guys where can i get units 4,5,6 2010 2011 2009 june and jan papersFor Jan 2011 https://studentforums.biz/pastpapers/edexcel-january-2011-examiners-reports-%28physics-chemistry-biology-maths%29/ (https://studentforums.biz/pastpapers/edexcel-january-2011-examiners-reports-%28physics-chemistry-biology-maths%29/)
2010 + 2009: https://studentforums.biz/pastpapers/edexcel-new-syllabus-biology-physics-chemistry-pastpapers!!!!!!!/ (https://studentforums.biz/pastpapers/edexcel-new-syllabus-biology-physics-chemistry-pastpapers!!!!!!!/)
Post by: **RoRo** on July 02, 2011, 11:58:35 am
How many subjects?
Biology A2 but it's CIE and I'm going to be in my first year of uni as well... it's complicated to explain why am I doing the A2, but I plan to apply in another uni abroad and that's why I need the A-levels, and I'm going to start uni now [as in next semester] because if I don't get to travel abroad, I would have already guaranteed myself a seat in a uni!
Post by: Malak on July 02, 2011, 01:22:14 pm
Biology A2 but it's CIE and I'm going to be in my first year of uni as well... it's complicated to explain why am I doing the A2, but I plan to apply in another uni abroad and that's why I need the A-levels, and I'm going to start uni now [as in next semester] because if I don't get to travel abroad, I would have already guaranteed myself a seat in a uni!
Depends on how fast you can cover up the syllabus..
Its july already...Maybe give the unit 3 in jan and the unit 4 in june?
Post by: **RoRo** on July 02, 2011, 02:27:13 pm
Depends on how fast you can cover up the syllabus..
Its july already...Maybe give the unit 3 in jan and the unit 4 in june?
Yeaa, that's what I was thinking of!
Post by: Malak on September 09, 2011, 03:21:50 pm
Okay, i got a question.
Suggest a suitable experimental tech. for measuring the rate of reaction for:
(a) ethly ethanoate with sodium hydroxide.
(b) copper(II) ions with ammonia molecules.
I know that we cant use the tech. of measuring the gas volume as no gas is given off in both also I cant use change in mass.
Thanks.
Post by: iluvme on September 09, 2011, 04:11:36 pm
Guess I need to revive this thread ::)
Okay, i got a question.
Suggest a suitable experimental tech. for measuring the rate of reaction for:
(a) ethly ethanoate with sodium hydroxide.
(b) copper(II) ions with ammonia molecules.
I know that we cant use the tech. of measuring the gas volume as no gas is given off in both also I cant use change in mass.
Thanks.
I'm not exactly sure since we've not yet covered this section.
How about measuring the decrease in concentrations of ethyl ethanoate and copper (II) ions per unit time and drawing a graph?
Post by: ~ Miss Relina ~ on September 09, 2011, 04:53:35 pm
Guess I need to revive this thread ::)
Okay, i got a question.
Suggest a suitable experimental tech. for measuring the rate of reaction for:
(a) ethly ethanoate with sodium hydroxide.
(b) copper(II) ions with ammonia molecules.
I know that we cant use the tech. of measuring the gas volume as no gas is given off in both also I cant use change in mass.
Thanks.
I'm not sure as I have just began studying the unit 4 from a couple of days but I think that this is in the 1st topic of rates here is a try :D for
(a) it could be PH change
(b) colorimetry due to copper compounds are colored
hope I helped ;) ahhh By the way Thanks for reviving that thread needed that alot ;D
Post by: Malak on September 09, 2011, 07:48:22 pm
Why?
Sorry, I can be dumb at times ::)
Post by: ~ Miss Relina ~ on September 09, 2011, 07:54:59 pm
^ Well, yeah your answers are right but please if you could explain me.for (a) that reaction you gave gives neutral products Ch3coona+ c2h5oh +h2o so to be able to measure rate the most suitable method is the PH change due to NaOH being used up so PH may Decrease as nuetral products formed
Why?
Sorry, I can be dumb at times ::)
(b) copper is a transition metal so giving coloerd compound that why we use colorimetry as a blue copper ammonium compound fromed
hope u get it ;)
Post by: Malak on September 09, 2011, 07:56:48 pm
I really wonder at times how do I pass my exams ::)
Post by: ~ Miss Relina ~ on September 09, 2011, 09:03:55 pm
^ Oh thank you :D get it now ::)
I really wonder at times how do I pass my exams ::)
welcome
me too sometimes i feel i am stuck and i have the same ideas too ;D
Post by: Mike Benn on September 10, 2011, 09:37:10 am
Post by: Romeesa-Chan on September 10, 2011, 09:37:51 am
FInally A2 started..!!Good luck with it! ;)
Hated A2 Chem very much! =X
Post by: Malak on September 10, 2011, 11:22:23 am
Post by: ~ Miss Relina ~ on September 10, 2011, 11:25:55 am
Can anyone tell me why using a gas syringe method to collect gas in an experiment is better if the gas produced is soluble. :-\
because using the other method '' collecting gas under measuring cylinder fillde with water'' won't be suitable as the gas is soluble so will dissolve in water and won't be collected
hope you got it :)
Post by: The Golden Girl =D on September 18, 2011, 06:43:51 pm
This Q is about the rate of reaction Between 2-bromo-2-methylpropanone and sodium hydroxide.
Describe how the concentration of Hydroxide ions could be determined during the reaction.
My friend suggested Taking samples during the reaction and Doing titration to it , I just feel that that doesn't make sense at all or at least isn't doable o__O ::)
Thanks in Advance =]
Post by: Amelia on September 18, 2011, 07:19:43 pm
A2 Q on the way !! :P
This Q is about the rate of reaction Between 2-bromo-2-methylpropanone and sodium hydroxide.
Describe how the concentration of Hydroxide ions could be determined during the reaction.
My friend suggested Taking samples during the reaction and Doing titration to it , I just feel that that doesn't make sense at all or at least isn't doable o__O ::)
Thanks in Advance =]
I wonder if this (http://www.chemguide.co.uk/physical/basicrates/ordermech.html) gives the idea.
Post by: ~ Miss Relina ~ on September 20, 2011, 07:00:30 pm
A2 Q on the way !! :P
This Q is about the rate of reaction Between 2-bromo-2-methylpropanone and sodium hydroxide.
Describe how the concentration of Hydroxide ions could be determined during the reaction.
My friend suggested Taking samples during the reaction and Doing titration to it , I just feel that that doesn't make sense at all or at least isn't doable o__O ::)
Thanks in Advance =]
you could use Ph change as NaOH concentration change
Post by: The Golden Girl =D on September 20, 2011, 08:18:08 pm
Thanks =]
Post by: ~ Miss Relina ~ on September 20, 2011, 10:50:10 pm
For the record, It's an indirect way so we have to actually work out the concentration (by calculations).
Thanks =]
ur welcome
but you mean we have to calculate final concentration and that can be done by finding any of the reactants concentration and use equation to get the no. of moles of the NaOH reacted then by the known initial conc which gives the initial no.of moles we have { initial no.of moles - reacted no. of moles = unreacted/left no.of moles} this is used to get the conc of the NaOH left
but the way of keeping track of the conc of NaOH is using Ph ...etc
that's what u meant right ???
Post by: The Golden Girl =D on September 21, 2011, 04:20:47 pm
Post by: ~ Miss Relina ~ on September 21, 2011, 06:45:48 pm
Never mind, I got the idea , Thanks =]I also expected that you would be lost in last post sorry for too long explaination I tried to make the idea reach you but it seems that you may get confused :o :-[ :-[
Post by: The Golden Girl =D on September 21, 2011, 08:13:25 pm
Post by: ~ Miss Relina ~ on September 22, 2011, 11:38:00 am
My brain isn't functioning well since I've been studying for tomorrow's Quiz for many hours, so excuse me =]
then good luck ???
Post by: The Golden Girl =D on September 22, 2011, 02:27:08 pm
Post by: The Golden Girl =D on September 24, 2011, 02:08:05 pm
Rates of reactions in Unit 4 =.=
I just can't seem to figure out the Mechanisms in every Question I come across T_T and I have a Quiz on Monday so can someone please give some links or a website that will CLEARLY explain it to me.
Muj if you can share your Notes I'd be Thankful =]
Thanks in advance =]
Post by: Romeesa-Chan on September 24, 2011, 02:12:19 pm
A2 Q!
Rates of reactions in Unit 4 =.=
I just can't seem to figure out the Mechanisms in every Question I come across T_T and I have a Quiz on Monday so can someone please give some links or a website that will CLEARLY explain it to me.
Muj if you can share your Notes I'd be Thankful =]
Thanks in advance =]
Is it with the SN1 and SN2 mechanism ?
Post by: The Golden Girl =D on September 24, 2011, 02:13:19 pm
Is it with the SN1 and SN2 mechanism ?
Nah it's the other Random ones/weird ones :-\
Post by: Romeesa-Chan on September 24, 2011, 02:14:29 pm
Nah it's the other Random ones/weird ones :-\
Which page ? =S
Post by: The Golden Girl =D on September 24, 2011, 02:17:04 pm
Which page ? =SHmm like A + B -> AB2
which one is supposed to be the slow step and which the fast step .... And what kind of mechanism does it have. and stuff .
Post by: Banana on September 24, 2011, 02:20:33 pm
A2 Q!
Rates of reactions in Unit 4 =.=
I just can't seem to figure out the Mechanisms in every Question I come across T_T and I have a Quiz on Monday so can someone please give some links or a website that will CLEARLY explain it to me.
Muj if you can share your Notes I'd be Thankful =]
Thanks in advance =]
Check your box ::)
Post by: Romeesa-Chan on September 24, 2011, 02:20:58 pm
Hmm like A + B -> AB2
which one is supposed to be the slow step and which the fast step .... And what kind of mechanism does it have. and stuff .
Try this, love:
http://www.chemguide.co.uk/physical/basicrates/orders.html#top
If it's not helpful then lemme know, I shall explain it in my words.
Post by: The Golden Girl =D on September 24, 2011, 02:22:24 pm
Try this, love:
http://www.chemguide.co.uk/physical/basicrates/orders.html#top
If it's not helpful then lemme know, I shall explain it in my words.
Thanks for the link love but it doesn't have the mechanism thing :-\
Post by: The Golden Girl =D on September 24, 2011, 02:30:38 pm
Post by: Romeesa-Chan on September 24, 2011, 02:37:17 pm
Thanks for the link love but it doesn't have the mechanism thing :-\I am not getting which mechanism. =/
Sn1 and Sn2 were the main ones and well. . . the book explains it alright.
Post by: The Golden Girl =D on September 24, 2011, 02:38:12 pm
I am not getting which mechanism. =/
Sn1 and Sn2 were the main ones and well. . . the book explains it alright.
Then maybe the SN1 and SN2 ones I don't get , can u explain them for me =]
Post by: Romeesa-Chan on September 24, 2011, 02:42:17 pm
Then maybe the SN1 and SN2 ones I don't get , can u explain them for me =]
Sure lovely. ;D
Gimme some time.
I will get back to you. (:
Post by: Romeesa-Chan on September 24, 2011, 05:22:02 pm
-Only one reactant
-Formation of primary carbocation before reacting with OH- ions therefore OH- ions do NOT appear in the rds (rate determining step).
Changing the concentration of OH- ions does not alter the rate of reaction.
-> Sn2 mechanism:
-2 reactants present
-Both OH- ions and the Halogenoalkane are present in the rds therefore concentration of both the reactants is vital
*learning how to draw the mechanisms are compulsary
ps - Reaction rate diagrams (for zero, first and second order reactions) will always come so make sure that you learn those as well.
Post by: ~ Miss Relina ~ on September 24, 2011, 06:18:48 pm
Post by: Malak on September 27, 2011, 03:45:20 pm
the book says what's the realtionship between the neutralisation and redox ??? any websites I would be grateful :DSorry for the late reply.
I am no quite sure, i guess we both use the same book so if you can refer to me to the Q page or anything then I can be of better help.
Post by: Amelia on September 27, 2011, 05:13:35 pm
the book says what's the realtionship between the neutralisation and redox ??? any websites I would be grateful :D
How can they be related? Two completely different reactions. :-\
Redox reactions are oxidation (lose of electrons) and reduction (gain of electrons) reaction.
Neutralization reaction is the combination of acid (H+ ions) and base (OH- ions) to give a salt, with no electron transfer whatsoever.
So, yeah. Something's up with the question. ::) :P
Post by: The Golden Girl =D on September 27, 2011, 07:00:52 pm
Post by: ~ Miss Relina ~ on September 27, 2011, 08:08:17 pm
@Amelia I think there is a relation but I don't know exactly
@Golden girl : acid-base equilibria
Post by: The Golden Girl =D on September 28, 2011, 12:59:06 pm
Post by: ~ Miss Relina ~ on September 28, 2011, 01:08:52 pm
I can't you since We haven't started it at school =[
anyways Thanks alot for ur respond
Post by: ~ Miss Relina ~ on September 28, 2011, 02:31:58 pm
Q4(aii) how do I know the initial moles exactly ???
http://www.xtremepapers.com/Edexcel/Advanced%20Level/Chemistry/2002%20Jan/Question%20Paper%20Jan%202002%20Unit-4.pdf
Post by: Malak on September 28, 2011, 06:38:47 pm
well guys i need that question to be killed as it's driving me mad and I don't what's up with me :o :o :oAre you sure its the right Question :S
Q5(aii) how do I know the initial moles exactly ???
http://www.xtremepapers.com/Edexcel/Advanced%20Level/Chemistry/2002%20Jan/Question%20Paper%20Jan%202002%20Unit-4.pdf
Q5 a ii asks for a reagent :-\ not moles.
Post by: ~ Miss Relina ~ on September 28, 2011, 06:41:44 pm
Are you sure its the right Question :Ssorry
Q5 a ii asks for a reagent :-\ not moles.
EDIT : Q4 a(ii)
Post by: ~ Miss Relina ~ on September 30, 2011, 11:48:53 pm
Post by: Romeesa-Chan on October 01, 2011, 12:09:26 am
so plz guys help is urgent here asap :-[I am sorry but I have no idea ... >_<
Hope GG or Ang3l can help you out ... :-[
Post by: The Golden Girl =D on October 01, 2011, 07:52:50 am
Post by: ~ Miss Relina ~ on October 01, 2011, 08:31:22 am
thx for trying to help ;) :) :D ;D really appreaciated
I'm not the who one makes her students upset ;D ;D ;D ;D
Post by: Banana on October 01, 2011, 08:52:31 am
okay guys Thanks alot for ur respond I've got it from other place
thx for trying to help ;) :) :D ;D really appreaciated
I'm not the who one makes her students upset ;D ;D ;D ;D
Can you tell us the answer? :-\
Post by: Amelia on October 01, 2011, 08:57:42 am
sorry
EDIT : Q4 a(ii)
I'm glad you managed to find the answer, Relina, but for the sake of other's benefit I'll clear it out. ;)
2SO3(g) <----> 2SO2(g)+ O2(g)
Moles at the start of the experiment: 2 (for SO3) 0 (for SO2) 0 (for O2)
Moles at equilibrium: 1.5 (for SO2 ---> "75% of SO3", so you have to do 75% of the initial 2moles of SO3), O.5 (for SO3, because 75% has been disassociated; subtract the moles of initial moles of SO3 with the equilibrium moles of SO2) and 0.5 moles of 02 (you did notice in the equation there's only one mole of O2, so it's half of SO2 in the equilibrium.)
and than you have to find out the partial pressure, I guess y'all know how to do that.
P.S - Sorry for the late reply.
Post by: Banana on October 01, 2011, 09:27:23 am
I'm glad you managed to find the answer, Relina, but for the sake of other's benefit I'll clear it out. ;)2SO3(g) <----> 2SO2(g)+ O2(g)
Moles at the start of the experiment: 2 (for SO3) 0 (for SO2) 0 (for O2)
Moles at equilibrium: 1.5 (for SO2 ---> "75% of SO3", so you have to do 75% of the initial 2moles of SO3), O.5 (for SO3, because 75% has been disassociated; subtract the moles of initial moles of SO3 with the equilibrium moles of SO2) and 0.5 moles of 02 (you did notice in the equation there's only one mole of O2, so it's half of SO2 in the equilibrium.)
and than you have to find out the partial pressure, I guess y'all know how to do that.
P.S - Sorry for the late reply.
Thanks fer the help ;)
Post by: ~ Miss Relina ~ on October 01, 2011, 11:44:13 am
I'm glad you managed to find the answer, Relina, but for the sake of other's benefit I'll clear it out. ;)I was also going to post the answer but mine was a different one as ur answer is like the mark sheme and what I didn't undersatnd from it is from where did he get the initial moles ???from equation ???2SO3(g) <----> 2SO2(g)+ O2(g)
Moles at the start of the experiment: 2 (for SO3) 0 (for SO2) 0 (for O2)
Moles at equilibrium: 1.5 (for SO2 ---> "75% of SO3", so you have to do 75% of the initial 2moles of SO3), O.5 (for SO3, because 75% has been disassociated; subtract the moles of initial moles of SO3 with the equilibrium moles of SO2) and 0.5 moles of 02 (you did notice in the equation there's only one mole of O2, so it's half of SO2 in the equilibrium.)
and than you have to find out the partial pressure, I guess y'all know how to do that.
P.S - Sorry for the late reply.
Post by: ~ Miss Relina ~ on October 01, 2011, 11:50:49 am
Thanks fer the help ;)really sorry for late reply I'll post now the way I found it so that u would use it too:
At a particular temperature, 75% of the sulphur trioxide is dissociated, producing a
pressure of 10 atm. Calculate the value of Kp at this temperature paying, attention to its units.
OK You are given the equation:
2SO3 --> 2SO2 + O2
If 75% of the SO3 dissociates it leaves 25% undissociated.
.. and as 1 mole of SO3 produces 1 mole of SO2 there will be 75% of the original moles of SO3 made into SO2 (and half that of O2 )
And, you are told that the overall pressure is 10atm.
Well, total pressure = sum of the partial pressures.
Let initial moles of SO3 = x
Final moles of SO3 = 0.25x
Final moles of SO2 = 0.75x
Final moles of O2 = 0.375x
Sum of moles = 1.375 = 10 atm
PP of SO3 = 0.25/1.375 x 10 = 1.818
PP of SO2 = 0.75/1.375 x 10 = 5.455
PP of O2 = 0.375/1.375 x 10 = 2.727
kp = (5.455)(5.455)(2.727)/(1.818 x 1.818) = 24.55 atm
hope u get it ;D and accept my apologise :)
Post by: Banana on October 01, 2011, 11:55:08 am
Let initial moles of SO3 = x
Final moles of SO3 = 0.25x
Final moles of SO2 = 0.75x
Final moles of O2 = 0.375x
hope u get it ;D and accept my apologise :)
Thanks a lot :) But when you found the final moles aren't you supposed to multiply the SO3 moles by 2 as per the equation? :-\
Post by: ~ Miss Relina ~ on October 01, 2011, 11:58:14 am
Thanks a lot :) But when you found the final moles aren't you supposed to multiply the SO3 moles by 2 as per the equation? :-\
no 0.25x is already multiplied but for for equation u have O2 half SO2 that's why dividing 0.75x/2= 0.375x
Post by: Banana on October 01, 2011, 12:00:58 pm
no 0.25x is already multiplied but for for equation u have O2 half SO2 that's why dividing 0.75x/2= 0.375x
Aha I see...that's simpler to understand ;D Thanks a lot, yo...this'll help me a lot in unit 4 :D
Post by: ~ Miss Relina ~ on October 01, 2011, 12:01:48 pm
Aha I see...that's simpler to understand ;D Thanks a lot, yo...this'll help me a lot in unit 4 :D
u're welcome :D
Post by: **RoRo** on October 03, 2011, 10:18:21 pm
Post by: Deadly_king on October 05, 2011, 09:42:29 pm
http://www.chemguide.co.uk/basicorg/isomerism/optical.html
http://chemistry.umeche.maine.edu/CHY252/stereo.html
http://webhost.bridgew.edu/fgorga/Stereochem/chiral.htm
http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/sterism2.htm
http://www.elmhurst.edu/~chm/vchembook/209optical.html
Post by: ~ Miss Relina ~ on October 15, 2011, 05:33:11 pm
Thanks
and other one too what is the effect of increasing chain length on Pka of carboxylic acids
and why ????
Post by: SZM on October 17, 2011, 11:37:06 pm
do u understand the concept based on- How fast? Rates of chemical change?????
If so, can u explain me in details with simple english in bullet point form on
1. techniques to measure rate of reaction
2. rate equations, rate constants and the order of a reaction
3. determining the order of a reaction and the rate equation from experimental data.
4.graphical represnentation of kinetic measurements.
5. activation energy and types of catalyst
6. investigating the activation energy of a reaction
7. relating a mechanism to the rate-determining step
8. the mechanism of the reaction of iodine with propane.
pls help me dear....
i need ur reply urgenlty.
these questions are from edexcel A2 chemistry in unit 4///
Post by: SZM on October 17, 2011, 11:52:34 pm
i was waiting 4 ur reply.
pls send ur reply very soon...
Post by: iluvme on October 18, 2011, 03:13:23 pm
So I suppose I couldn't help you much, though take a look here, it might help you immensely InshaAllah :)
http://www.s-cool.co.uk/a-level/chemistry/reaction-kinetics
Post by: The Golden Girl =D on October 19, 2011, 02:56:01 pm
several grams(an excess) of magnesium hydroxide are added to 1 dm3 of water at 289 K (room temperature). The solution becomes Saturated when 10.31*10-4 moles of magnesium hydroxide had dissolved.
Calculate the pH of this solution ,given that Kw = 1*10-14 mol2dm-6 at 289 K.
That the only thing given in the Question as well as the following Equation;
Mg(OH)2 (s) +aq <-> Mg-2 (aq) +2OH- (aq)
Thanks in Advance =D
Post by: The Golden Girl =D on October 19, 2011, 03:07:29 pm
Post by: Amelia on October 19, 2011, 03:53:37 pm
I hope someone helps me with this cuz it's H.W. and I'm dead meat if I don't do it :-X :-\
several grams(an excess) of magnesium hydroxide are added to 1 dm3 of water at 289 K (room temperature). The solution becomes Saturated when 10.31*10-4 moles of magnesium hydroxide had dissolved.
Calculate the pH of this solution ,given that Kw = 1*10-14 mol2dm-6 at 289 K.
That the only thing given in the Question as well as the following Equation;
Mg(OH)2 (s) +aq <-> Mg-2 (aq) +2OH- (aq)
Thanks in Advance =D
Dont blame me, if it's wrong. Not my work, anyway. :P
"you need to work out how many OH- ions are in solution.
10.31 x 10^-4 moles of Mg(OH)2 means twice as many OH- ions
You know how many moles of OH- are in that dm3 and you know that [H+] x [OH-] = 1 x 10^-14 so divide 1x10^-14 by the [OH-] to get the H+ concentration. Then use -log of that to get the pH."
Post by: Banana on October 19, 2011, 04:52:47 pm
But just to be more clear...find the moles of Mg(OH)2 first...then muultiply by 2 to find moles of OH1-
Then you find the conc. of OH1-= n/v
Find the H+ conc by dividing the Kw by the OH1- conc...
pH= -loh H+...as Amelia said ;)
I'm too lazy to do the calculations :P
Post by: Blizz_rb93 on October 20, 2011, 09:52:22 am
2NH3 (aq) + H2SO4 (aq) --> (NH4)2SO4 (aq)
a) Calculate the theoretical maximum yield that can be obtained by reacting 25.0cm3 of 2.0mol dm-3 ammonia solution with an excess of sulfuric acid
can someone help me figure this out? I dont know what to do :( i tried finding amount of NH3 by amount of substance in solution = volume x conc. and then finding its mass then using mole ratio to find mass of sulfuric acid but i always got wrong answer can someone explain the method?
thank you
Post by: The Golden Girl =D on October 20, 2011, 02:26:47 pm
Post by: Amelia on October 20, 2011, 05:01:20 pm
A Student prepared a sample of the fertilizer ammonium sulfate by adding ammonia solution to sulfuric acid:
2NH3 (aq) + H2SO4 (aq) --> (NH4)2SO4 (aq)
a) Calculate the theoretical maximum yield that can be obtained by reacting 25.0cm3 of 2.0mol dm-3 ammonia solution with an excess of sulfuric acid
can someone help me figure this out? I dont know what to do :( i tried finding amount of NH3 by amount of substance in solution = volume x conc. and then finding its mass then using mole ratio to find mass of sulfuric acid but i always got wrong answer can someone explain the method?
thank you
"From the equation:
2mol NH3 will produce 1 mol (NH4)2SO4
Mol NH3 in 25.0cm³ of 2.0M NH3 = 25/1000*2 = 0.05 mol NH3
This will produce 0.05/2 = 0.025 mol (NH4)2SO4
Molar mass (NH4)2SO4 = 132.14 g/mol
0.025mol = 0.025*132.14 = 3.30g (NH4)2SO4"
Allright?
Post by: Blizz_rb93 on October 22, 2011, 09:38:48 am
Most welcome, GG. :)
"From the equation:
2mol NH3 will produce 1 mol (NH4)2SO4
Mol NH3 in 25.0cm³ of 2.0M NH3 = 25/1000*2 = 0.05 mol NH3
This will produce 0.05/2 = 0.025 mol (NH4)2SO4
Molar mass (NH4)2SO4 = 132.14 g/mol
0.025mol = 0.025*132.14 = 3.30g (NH4)2SO4"
Allright?
ohh okay i get it now thank you! :)
Post by: The Golden Girl =D on October 22, 2011, 03:15:27 pm
This is what I wrote , I don't even know if it's right :'(
How does Blood act as a Buffer Solution?
Carbon dioxide (CO2) is a gaseous waste product from metabolism. The blood carries carbon dioxide to the lungs, where it is exhaled. More than 90% of carbon dioxide in the blood exists in the form of bicarbonate (HCO3) [which is a buffer found in blood plasma] . The rest of the carbon dioxide is either dissolved carbon dioxide gas (CO2) or carbonic acid (HCO3). The kidneys and lungs balance the levels of carbon dioxide, bicarbonate, and carbonic acid in the blood.
Carbon dioxide is mainly transported as (H2CO3) in the blood. It dissociates as follows:
H2CO3 HCO3? + H+
Since there will be more H+ available in the Blood , the pH will decrease .
Blood has to be kept at pH 7.4.
It is buffered using Carbonic Acid [H2CO3].
Reference:
http://www.webmd.com/a-to-z-guides/bicarbonate
^ it's incomplete as you can see :-[ :(
thanks =]
Post by: Amelia on October 22, 2011, 03:53:43 pm
Oxidation of glucose in the body for energy release.
C6H12O6+602---> 6CO2+6H20
Your blood is now left with a waste disposal problem, which is potentially poisonous. The problem and part of the solution, lies in the equation below. The rates of both forward and backward reactions in the equilibrium is rapid, thanks to the enzyme carbonic anhydrase.
H2O+CO2<--->H+ + HCO3-
The generation of H+ ions if unchecked, would lead to a lowering of blood pH and you would slip into a coma. Your blood needs a buffer.
There are three buffers in the blood.
1) HCO3- (hydrogencarbonate ions, the most important ones.
2) Haemoglobin
3) Plasma proteins.
Hydrogen ions in the blood are "mopped" up by hydrogen bicarbonate ions, the equation (above) in which the equilibrium is well to the left. The Co2 produced is carried to the lungs and breathed out.
(http://www.chemistry.wustl.edu/~edudev/LabTutorials/Buffer/images/Eqn1.jpg)
Post by: The Golden Girl =D on October 22, 2011, 03:58:36 pm
Post by: ~ Miss Relina ~ on October 22, 2011, 09:32:35 pm
Post by: Romeesa-Chan on October 22, 2011, 10:50:25 pm
why modern methods based on mass spectroscopic measurements of carbon isotope ratios are now used intead of carbon dating ??? anylinks plz :( :( :(
It is more accurate.
Post by: ~ Miss Relina ~ on October 23, 2011, 07:54:44 am
It is more accurate.
Thanks for contributing this is good one :D
but they need a kind of research and I searched but nothing found yet if u plz do have anything else post it I would be very thankful ;)
Post by: Romeesa-Chan on October 23, 2011, 03:13:49 pm
Thanks for contributing this is good one :D
but they need a kind of research and I searched but nothing found yet if u plz do have anything else post it I would be very thankful ;)
Welcome. (:
I tried doing a research on it as well but kinda failed at that. =/ Sorry. :-[
Post by: ~ Miss Relina ~ on October 25, 2011, 03:24:18 pm
Welcome. (:
I tried doing a research on it as well but kinda failed at that. =/ Sorry. :-[
no probs :-[ :)
Post by: The Golden Girl =D on October 26, 2011, 08:19:29 pm
it's done like this ;
[CO2] = 0.126 * 0.0224
[CO2]= 2.82*10-3
Part in RED : is what I got from part d)i)
I don't get why it's done that way :-\
I need this by tomorrow [would appreciate it if you did it for me ]
Thanks =]
Post by: ~ Miss Relina ~ on November 03, 2011, 03:21:47 pm
Q. 47] d)ii) => Attached
it's done like this ;
[CO2] = 0.126 * 0.0224
[CO2]= 2.82*10-3
Part in RED : is what I got from part d)i)
I don't get why it's done that way :-\
I need this by tomorrow [would appreciate it if you did it for me ]
Thanks =]
well I copied that form answers just to clarify it
hope that u get it or even understand that messy handwriting
Post by: The Golden Girl =D on November 03, 2011, 03:25:24 pm
Post by: ~ Miss Relina ~ on November 03, 2011, 03:25:46 pm
Post by: Banana on November 04, 2011, 04:18:17 am
Post by: SZM on November 04, 2011, 05:06:01 am
May I know are u doing edexcel or cambridge? If it is edexcel, which unit are u now?? are u doing alevel privately or schooling???
wat r the subjects u r doing for ur edexcel???? pls tel me about the experience towards alevel if u have done alevel exams atleast.
pls cn u tel me, is self study more than enough or should i attend the classes, as i am doing edexcel alevel privately. Pls can u tel me ur experience , ur suggestions, ur opinion to this matter.
pls tel me, wat r the best steps i should perform to achieve A* ??????
I need ur reply urgently dear..... :'( :'( :'(
Post by: ~ Miss Relina ~ on November 04, 2011, 07:23:48 am
Even I think its D...because transition elements do act as catalysts :-\
yes me too strange answer I guess :-\ :-\
Post by: ~ Miss Relina ~ on November 04, 2011, 07:39:45 am
Miss Relina.QuoteMay I know are u doing edexcel or cambridge? If it is edexcel, which unit are u now?? are u doing alevel privately or schooling???
wat r the subjects u r doing for ur edexcel???? pls tel me about the experience towards alevel if u have done alevel exams atleast.
well I'm edexcel ,I'm taking all the units(4,5,6 ), well no specific experience except study well practice new patpapers very well, and pray that you get what you hope isAQuotepls cn u tel me, is self study more than enough or should i attend the classes, as i am doing edexcel alevel privately. Pls can u tel me ur experience , ur suggestions, ur opinion to this matter.
actually I think it differs from person to other ,also depends on whether you feel that it's too hard on you and there is something missing you???
and whether teachers in your country are worth your time or not ;)Quotepls tel me, wat r the best steps i should perform to achieve A* ??????
study well practice new patpapers very well, and pray that you get what you hope isA
need ur reply urgently dear..... :'( :'( :'(
;)
Post by: Romeesa-Chan on November 04, 2011, 10:21:16 am
here is my turn ;)Which paper is it ?
Post by: SZM on November 04, 2011, 10:55:34 am
And Miss Relina, which materials are u using to study??? if u ahve extra notes, can u give me by scanning the notes dear?? becoz i dont hve notes dear///
u said study well, wat do u mean by that?? tel me in details???? how to grasp the concepts into my mind and how to mke these concepts in my mind forever???/ Did u understand the concepts of AS units weell?? if so, u taught u then???? pls tel me dear.. Hope u are muslim girl. if so, I am also muslim.
need ur reply urgently......
Post by: ~ Miss Relina ~ on November 04, 2011, 04:35:13 pm
Which paper is it ?
I don't know sorry I found it in those examwizard questions :-[ :-\ :-\
Miss Relina, wat about AS unit like unit 1 , 2 and 3?????? If u have done , may i know wat is ur results for ur AS level??? Dear r u doing edexcel A2 privately or schooling????
And Miss Relina, which materials are u using to study??? if u ahve extra notes, can u give me by scanning the notes dear?? becoz i dont hve notes dear///
u said study well, wat do u mean by that?? tel me in details???? how to grasp the concepts into my mind and how to mke these concepts in my mind forever???/ Did u understand the concepts of AS units weell?? if so, u taught u then???? pls tel me dear.. Hope u are muslim girl. if so, I am also muslim.
need ur reply urgently......
well As was okay but not so good I'll repeat 2 units so I've lots of work to do
well i don't know how to explain study well it differs from person to another Istudied from Ann fullick book
ohh so we inverse log 0.9 ..Ahaa , Thanks relina =D
ur welcome by the way I love ''that '' glasses ;)
anyone have got the examzone answers for the A2 book they are not in the A2 answers :-\ :-\ :-\
anyone have got the examzone answers for the A2 book they are not in the A2 answers :-\ :-\ :-\okay I found it AlhamdulliAllah
here it's for anyone who needs it too
https://studentforums.biz/reference-material-83/answers-for-the-a2-chemistry-edexcel-book-urgent-!!/
Post by: The Golden Girl =D on November 05, 2011, 12:23:13 pm
ur welcome by the way I love ''that '' glasses ;)
Thanks 'lifts glasses' :P =]
Post by: ~ Miss Relina ~ on November 05, 2011, 08:40:18 pm
I don't find alot of things so do they really matter or will they come in exams or it doesn't matter if I left them ??? :(
answer me soon plz :-\
Post by: Most UniQue™ on November 09, 2011, 10:40:10 am
Post by: ~ Miss Relina ~ on November 09, 2011, 01:49:13 pm
@ Relina : Please refrain from double posting. I have combined your posts . Thanks
oh....Thanks but did I double post ??? inbox me which post was doubled plz I would like to know
Post by: Most UniQue™ on November 09, 2011, 04:21:09 pm
oh....Thanks but did I double post ??? inbox me which post was doubled plz I would like to know
By double post , I mean posting one after another and not including them all in one post...
Post by: Malak on November 10, 2011, 03:34:33 pm
guys those sc signs in the A2 book drive me maaaaaaaaaaaad >:( >:( >:( >:(The sc parts are there to build your knowledge on that particular topic in a practical way. I dont think they come up in exam but its good to do some research about it as it might help
I don't find alot of things so do they really matter or will they come in exams or it doesn't matter if I left them ??? :(
answer me soon plz :-\
Post by: ~ Miss Relina ~ on November 11, 2011, 05:14:47 pm
The sc parts are there to build your knowledge on that particular topic in a practical way. I dont think they come up in exam but its good to do some research about it as it might helpok Thanks alot
Post by: ~ Miss Relina ~ on November 11, 2011, 05:15:03 pm
By double post , I mean posting one after another and not including them all in one post...
aha..now I understood Thanks
Post by: The Golden Girl =D on November 12, 2011, 09:54:50 am
(b) Alanine reacts with both acids and bases. Give the structural formulae of the compounds you would expect if alanine reacts with
hydrochloric acid
– NH3 +Cl– on the amino group (1)
sodium hydroxide
–COO– Na+ on the carboxyl group
....................................
d) Polyamides are made from a diacid dichloride and a diamine; they are condensation polymers.
(ii) Suggest the structural formula of a diacid dichloride and a diamine that could be reacted to form a polyamide.
(ii) any CIOC***COCl (1) and H2N*CH2*NH2 (1)
(iii) Draw sufficient of the polymer chain that would result from the reaction of the compounds in (ii) to make the structure of the polymer clear.
(iii) structure consequential on answer to (ii) showing amide link (1)
and extension of the chain
(iv) Alanine could be converted to CH3CH(NH2)COCl which on its own could polymerise to a polyamide. Draw the structure of the polymer chain showing three alanine repeating units and all the bonds in the amide links.
(iv) couldn't copy it -.-
I really didn't know how to draw them =[ so someone please draw them and tell me why it turned the way you drew it, Thanks =D
Post by: Malak on November 12, 2011, 12:18:44 pm
Post by: The Golden Girl =D on November 12, 2011, 12:20:12 pm
Relina , if you're out there and know what I'm talking about , please do reply :$
Thanks =]
Post by: Galleria on November 13, 2011, 09:21:13 am
http://www.chemsheets.co.uk/AS/CHEM2.2/AS.CHEM2.2.004.pdf
On enthalpy change:
http://www.chemsheets.co.uk/AS/CHEM2.1/AS.CHEM2.1.008.pdf
http://www.chemsheets.co.uk/AS/CHEM2.1/AS.CHEM2.1.009.pdf
PLEAAAASE AND THANK YOU ^_^
Post by: Malak on November 13, 2011, 01:41:21 pm
On reaction kinetics:I have merged your post with this thread, please post all your doubts in the specific thread from now on.
http://www.chemsheets.co.uk/AS/CHEM2.2/AS.CHEM2.2.004.pdf
On enthalpy change:
http://www.chemsheets.co.uk/AS/CHEM2.1/AS.CHEM2.1.008.pdf
http://www.chemsheets.co.uk/AS/CHEM2.1/AS.CHEM2.1.009.pdf
PLEAAAASE AND THANK YOU ^_^
Thanks.
Kinetics:
3 (b) i - 3, its basically the same 'cause the volume is halved and conc. is doubled
ii - Temperature is lowered so rate will decrease therefore its 4
iii - Conc. doubles so the volume produced doubles, its curve 1
iv - Catalyst therefore rate increases, its curve 2
(b) Do you want me to draw the graph for you?
ii - Of course, higher temperature because more molecules gain energy greater than or equal to the activation energy and therefore more successful collisions take place
iii - For a successful collision particles must collide in the correct orientation and with sufficient energy.
Post by: ~ Miss Relina ~ on November 13, 2011, 03:32:52 pm
It's old syllabus (don't know which one is it).
Relina , if you're out there and know what I'm talking about , please do reply :$
Thanks =]
it is not related to unit 4 I think it's from unit 5
tell us in which topic in examwizard u found that questions :-\ :-\
Post by: The Golden Girl =D on November 13, 2011, 05:08:43 pm
Thanks again =]
Post by: ~ Miss Relina ~ on November 13, 2011, 05:59:09 pm
Turns out IT IS from Unit 5 , no wonder I thought it was weird o.Ohahahaha............fine :P
Thanks again =]
you're welcome
Post by: ~ Miss Relina ~ on November 16, 2011, 10:30:29 pm
attached
Thanks in advance
Post by: Romeesa-Chan on November 16, 2011, 10:45:09 pm
Sorry. :-[
Was never good at the whole nmr thing. ::)
Post by: ~ Miss Relina ~ on November 17, 2011, 08:11:55 pm
I tried. Didn't get it.
Sorry. :-[
Was never good at the whole nmr thing. ::)
thx for trying I really appreciate it ;)
Post by: The Golden Girl =D on November 18, 2011, 01:38:17 pm
well here we go ;)
attached
Thanks in advance
I just made a random Guess but not sure if it's right.
It says CycloHexEne and Bromine.
1 for Bromide
1 for the DOUBLE Bond since it's an alkEne
1 for the C-H
I hope I helped =]
Post by: Romeesa-Chan on November 18, 2011, 01:55:17 pm
I just made a random Guess but not sure if it's right.But, it said the product of reaction between cyclohexene and bromine. :-\
It says CycloHexEne and Bromine.
1 for Bromide
1 for the DOUBLE Bond since it's an alkEne
1 for the C-H
I hope I helped =]
Post by: The Golden Girl =D on November 18, 2011, 02:08:34 pm
Post by: ~ Miss Relina ~ on November 18, 2011, 07:02:24 pm
Ohh then it's goot be two ,right ?well I think your first trial is fine as I did it like that too
Post by: ~ Miss Relina ~ on November 18, 2011, 07:14:04 pm
sorry but another Q is here to tell me why it is C not B
attached
Post by: Romeesa-Chan on November 18, 2011, 07:31:48 pm
sorry but another Q is here to tell me why it is C not B
attached
The reaction is between a strong acid and a strong base.
We know that endpoint for this reaction will be 7.
Thymolphthalein gives pH range of 8.3-10.6 which is specific for our end point.
Universal indicator has a wider range of pH, look for a pH range that's more specific to the endpoint.
Hope that's cleared. (:
Post by: ~ Miss Relina ~ on November 18, 2011, 08:39:35 pm
The reaction is between a strong acid and a strong base.
We know that endpoint for this reaction will be 7.
Thymolphthalein gives pH range of 8.3-10.6 which is specific for our end point.
Universal indicator has a wider range of pH, look for a pH range that's more specific to the endpoint.
Hope that's cleared. (:
Jazaki Allah Kairan my beloved ;)
well I want to ask u about unit 6B actually I've tested myself by doing the specimen but it really sucks :'( :'( :-X
and when I browsed pastpapers of unit 6 they really don't help I thought that old papers would be helpful as in last year of unit 3
so what should I do ........ :-\ :-\ as I need to be well prepared for jan :-[
Post by: Romeesa-Chan on November 18, 2011, 08:52:09 pm
Jazaki Allah Kairan my beloved ;)JazakAllah khairon. <3
well I want to ask u about unit 6B actually I've tested myself by doing the specimen but it really sucks :'( :'( :-X
and when I browsed pastpapers of unit 6 they really don't help I thought that old papers would be helpful as in last year of unit 3
so what should I do ........ :-\ :-\ as I need to be well prepared for jan :-[
Your giving 6B in Jan ?
Have you covered up Unit 4 and Unit 5 already ?
Well, use the notes here (https://studentforums.biz/reference-material-83/edexcel-chemistry-and-physics-unit-6b/) and after you learning these then read and go through the chemistry practical investigations. (https://studentforums.biz/reference-material-83/edexcel-practical-investigations-for-a2-physics-and-a-level-chemistry/)
Make sure that your concept on both Unit 4 and 5 of Chemistry is very clear. ;)
Do the papers again and again. Read the ER. The exam question pattern must be stamped into your head.
If you need anything else, please feel free to ask. ;)
Post by: ~ Miss Relina ~ on November 19, 2011, 08:18:40 am
JazakAllah khairon. <3
Your giving 6B in Jan ?
Have you covered up Unit 4 and Unit 5 already ?
Well, use the notes here (https://studentforums.biz/reference-material-83/edexcel-chemistry-and-physics-unit-6b/) and after you learning these then read and go through the chemistry practical investigations. (https://studentforums.biz/reference-material-83/edexcel-practical-investigations-for-a2-physics-and-a-level-chemistry/)
Make sure that your concept on both Unit 4 and 5 of Chemistry is very clear. ;)
Do the papers again and again. Read the ER. The exam question pattern must be stamped into your head.
If you need anything else, please feel free to ask. ;)
yes I'll do it in Jan isA
yes but not quite well prepared I studied from that blue book of Ann fullick and seems it is not sufficient :-[
I'll try but.........as I find some difficulties while anwsering jan 2011 so are there any resources which are covering up the syllabus or even giving hints about what the syllabus want as it's really vague..... :-\ :-\ :-\
Thanks for advice Jazaki Allah Kairan :)
Post by: ~ Miss Relina ~ on November 20, 2011, 06:06:08 pm
Post by: Romeesa-Chan on November 22, 2011, 10:38:55 pm
anyone plz do reply ???
Do you have the final answer ? :)
Post by: dk bose on November 24, 2011, 11:03:51 am
(a)Aluminium is extracted by electrolysis of Al2O3.What is the maximum mass of the metal that could be obtained from 1 tonne of the oxide?
(b)If the yield of the electrolysis plant is 90%,what mass of the oxide must be used to produce 1 tonne of aluminium?
Post by: ~ Miss Relina ~ on November 28, 2011, 04:57:06 pm
why the product is benzoic acid ???
anyone :-[
Post by: ~ Miss Relina ~ on November 29, 2011, 01:55:14 pm
Do you have the final answer ? :)
it's -60 Kjmol
Post by: The Golden Girl =D on November 29, 2011, 02:25:18 pm
reaction of adrenaline and hot alkaline KMno4......... ???
why the product is benzoic acid ???
anyone :-[
I've seen this QUESTION before and it made me go from this :) to this >.< :P
Anyways one sec,
firstly I'm ONLY doing Unit 4 so I've very sorry but if it's Unit 5 then I'm not the one to answer :-\
What I know is that KMnO4 is an oxidizing agent so the Oh groups will disappear but that's all I can answer you for now.
I hope I helped =]
Post by: guMnam on November 29, 2011, 05:18:22 pm
reaction of adrenaline and hot alkaline KMno4......... ???where did you get this question from :S
why the product is benzoic acid ???
anyone :-[
Post by: ~ Miss Relina ~ on November 29, 2011, 05:25:35 pm
where did you get this question from :Shttp://www.xtremepapers.com/Edexcel/Advanced%20Level/Chemistry/1997%20Jan/Question%20Paper%20Jan%201997%20Unit-4.pdf
Q5 (a) (iv)
plz tell me the steps or how it came out
and if you know how to reply to my previous post about enthalpy of reaction plz do reply
Thanks in advance ;) :-[
Post by: dk bose on November 30, 2011, 10:15:55 am
Post by: The Golden Girl =D on November 30, 2011, 10:33:23 am
hey,people!! could anyone try to solve my this doubt???the question is as follows-
(a)Aluminium is extracted by electrolysis of Al2O3.What is the maximum mass of the metal that could be obtained from 1 tonne of the oxide?
(b)If the yield of the electrolysis plant is 90%,what mass of the oxide must be used to produce 1 tonne of aluminium?
Can someone answer his doubt please =]
* I forgot the AS Chemistry calculations -.- *
Post by: Malak on November 30, 2011, 05:34:13 pm
seems, that no one is able to answer my question or doesnt want to answer it????There should be some sort of an equation? :-\
Post by: ~ Miss Relina ~ on December 01, 2011, 09:28:15 am
I've seen this QUESTION before and it made me go from this :) to this >.< :P
Anyways one sec,
firstly I'm ONLY doing Unit 4 so I've very sorry but if it's Unit 5 then I'm not the one to answer :-\
What I know is that KMnO4 is an oxidizing agent so the Oh groups will disappear but that's all I can answer you for now.
I hope I helped =]
ya it did same to me ::)
what kind of question is this ???
anyways Thanks alot
Post by: The Golden Girl =D on December 01, 2011, 11:40:51 am
IKR -.-
You're Welcome =]
Post by: ~ Miss Relina ~ on December 01, 2011, 06:12:36 pm
attached also mark scheme is attached if anyone needs it ........ how did he get the no.of moles of the weak acid ???
Q 2 (d) iii
Post by: The Golden Girl =D on December 01, 2011, 07:08:18 pm
10 cm3 of NaOH reacted with 25 cm3 of the Weak acid ,so * if I subtract the 10 from the 25 then it'd be 15 cm3 remaining volume of weak acid.
*Why I subtracted it without feeling that I did something wrong is that in terms of concentration the ratio of the Weak acid to the Base is 1:1
so (15/1000 dm3) * (0.1 moldm-3) = 0.0015 moles
^ that could be a possibility , but not sure if it's right.
I hope I helped =]
Post by: ~ Miss Relina ~ on December 01, 2011, 09:37:45 pm
I've been thinking about it for the past few minutes so I'll tell you what I came up with.
10 cm3 of NaOH reacted with 25 cm3 of the Weak acid ,so * if I subtract the 10 from the 25 then it'd be 15 cm3 remaining volume of weak acid.
*Why I subtracted it without feeling that I did something wrong is that in terms of concentration the ratio of the Weak acid to the Base is 1:1
so (15/1000 dm3) * (0.1 moldm-3) = 0.0015 moles
^ that could be a possibility , but not sure if it's right.
I hope I helped =]
Thanks .........that's a good possibility but wait ............mmmmm....I think the buffer id formed ofweak acid/weak base andits conjucate acid/ base so NaOH is a strong acid .................well never mind I wrote what I thought at the moment right now ;D ;D ;D they're annoying me
but anyways I loved your possibilty and I'll accept it ;D ;D ;)
Post by: The Golden Girl =D on December 02, 2011, 09:33:09 am
Thanks ,I'm honored =D :P
Post by: ~ Miss Relina ~ on December 02, 2011, 04:03:56 pm
NaOH is a Base By the way ;)
Thanks ,I'm honored =D :P
that's the evil question effect on me ;)
By the way, did you prepared yourself for unit 4 practical or not yet ???
Post by: The Golden Girl =D on December 02, 2011, 04:05:46 pm
Not yet :$
Post by: ~ Miss Relina ~ on December 06, 2011, 03:17:46 pm
if an aqueous sodium nitrite, NaNO2 and added to it 10 drops of sulphuric acid in a conical flask
then from a burette containing potassium manganate titration is carried out .............
observation:
blue solution
brown gas
why ??? explain the observation plz
5NO2–(aq) + 2MnO4–(aq) + 6H+(aq) ? 5NO3–(aq) + 2Mn2+(aq) + 3H2O(l)
Post by: jackfos92 on December 09, 2011, 01:05:36 pm
if yes, is it more soluble than water?
Post by: dk bose on December 09, 2011, 02:17:38 pm
hey,people!! could anyone try to solve my this doubt???the question is as follows-This is a question from the edexcel AS chemistry revision guide,from the end of the first chapter's "Practice exam questions"!!
(a)Aluminium is extracted by electrolysis of Al2O3.What is the maximum mass of the metal that could be obtained from 1 tonne of the oxide?
(b)If the yield of the electrolysis plant is 90%,what mass of the oxide must be used to produce 1 tonne of aluminium?
Could plzz someone solve this question and give me the solutions as fast as possible!!
Post by: AS01 on December 09, 2011, 05:04:54 pm
Post by: Romeesa-Chan on December 09, 2011, 05:08:10 pm
is phenol soluble in ethanoic acid?
if yes, is it more soluble than water?
Not sure about it's solubility in Ethanoic acid.
But, Phenol is moderately soluble in water - about 8 g of phenol will dissolve in 100 g of water.
If you try to dissolve more than this, you get two layers of liquid. The top layer is a solution of phenol in water, and the bottom one a solution of water in phenol. The solubility behaviour of phenol and water is complicated, and beyond A level.
Phenol is somewhat soluble in water because of its ability to form hydrogen bonds with the water.
Post by: ~ Miss Relina ~ on December 09, 2011, 10:19:35 pm
is the question attached is neded by our Edxecel syllabus ...........????
need reply soon as my exams are toooooo close :-\
Post by: MKh on December 10, 2011, 02:51:33 pm
plz answer me
is the question attached is neded by our Edxecel syllabus ...........????
need reply soon as my exams are toooooo close :-\
I m not really sure but, as far as i know, Raoult's Law is not required by our new Edexcel GCE Chemistry specification.
If u hav a marking scheme for this question, just hav a look at the answer for this question.
Post by: The Golden Girl =D on December 10, 2011, 04:29:39 pm
Sometimes the concentration of the acid and base are NOT 1:1 and in such cases I don't know how to figure out the Equivalence Vloume.
Example :
when 0.20 M NaOH reacts with 0.10 M of Ch3COOH. the acid is 20 cm3 , Why does the Equivalence Volume is equal to 10 cm3 , why is it NOT 40 cm3 ?
if the ratio is 1 : 1 as in 0.1 M of NaOH and 0.1 M of Ch3COOH (volume of acid is 25 cm3 ) then equivalence Volume is 25 cm3 cuz they are 1:1 , same concentration that is.
My teacher said he'll make the concentrations different to trick us so I NEED ot know this BEFORE tomorrow since my exams is Tomorrow so PLEASE Help !
I'm asking this Question cuz I ALWAYS get the equivalence Volume WRONG when I draw the Titration Curve.
Thanks in Advance =D
[ I'll check this in a few hours from now cuz I need to study the rest of the Topics ]
Post by: Romeesa-Chan on December 10, 2011, 04:54:42 pm
The ratio of 1:1 is for strong acid and strong base.
Weak acid and strong base or weak base and strong acid will have a different curve therefore a different equivalence point.
Aren't they explained in the textbook ? :-\
PS- Check this site. :) (http://www.chemguide.co.uk/)
Post by: The Golden Girl =D on December 10, 2011, 05:01:00 pm
What I don't understand is how to determine the Equivalence Volume.
just like in the examples I gave =]
Post by: iluvme on December 10, 2011, 05:09:52 pm
As for your question, try using C1V1=C2V2.
Post by: The Golden Girl =D on December 10, 2011, 05:11:46 pm
can you elaborate a bit :$ :$
Post by: iluvme on December 10, 2011, 05:14:07 pm
Post by: The Golden Girl =D on December 10, 2011, 05:16:03 pm
Romeesa thanks By the way <3
Post by: iluvme on December 10, 2011, 05:17:19 pm
But are you sure? Even if your teacher hasn't taught you about it?
Post by: The Golden Girl =D on December 10, 2011, 05:19:54 pm
Post by: Romeesa-Chan on December 10, 2011, 06:03:25 pm
I understand this fully Alhamdulilah =]
What I don't understand is how to determine the Equivalence Volume.
just like in the examples I gave =]
Honey, you see the titration curve, yes ?
Take the midpoint of the straight line. A horizontal line should be drawn to that midpoint to obtain the equivalence point.
Did you get it now ? (:
Post by: ~ Miss Relina ~ on December 10, 2011, 08:27:45 pm
??? ???
Post by: ~ Miss Relina ~ on December 10, 2011, 08:29:30 pm
I m not really sure but, as far as i know, Raoult's Law is not required by our new Edexcel GCE Chemistry specification.
If u hav a marking scheme for this question, just hav a look at the answer for this question.
Thanks
Post by: The Golden Girl =D on December 11, 2011, 06:40:09 am
I think it's because NH3 is a WEAK Base.
A : HCl and NaOH => since it's STRONG Acid then it has HIGH concentration of Hydrogen Ions.
B : HCl and NaCl => since it's STRONG Acid and hence has HIGH concentration of Hydrogen Ions.
C : NH3 and it's salt => It's a WEAK Base so most likely to have LOWEST concentration of Hydrogen Ions!
D : CH3COOH and it's salt => has Low Hydrogen Ions since it's a WEAK Acid.
Bases have plenty of OH- Ions where as Acids have plenty of H+ Ions. In other words , the Base has fewer [H+] than the Weak Acid =D
I just tried to make sense out of it so that I make myself understand it so I'm not 100 % sure but that's how I got it =]
I hope I helped :)
Post by: ~ Miss Relina ~ on December 11, 2011, 06:09:28 pm
Relina , I don't know if I'll be of much help but here I go =]
I think it's because NH3 is a WEAK Base.
A : HCl and NaOH => since it's STRONG Acid then it has HIGH concentration of Hydrogen Ions.
B : HCl and NaCl => since it's STRONG Acid and hence has HIGH concentration of Hydrogen Ions.
C : NH3 and it's salt => It's a WEAK Base so most likely to have LOWEST concentration of Hydrogen Ions!
D : CH3COOH and it's salt => has Low Hydrogen Ions since it's a WEAK Acid.
Bases have plenty of OH- Ions where as Acids have plenty of H+ Ions. In other words , the Base has fewer [H+] than the Weak Acid =D
I just tried to make sense out of it so that I make myself understand it so I'm not 100 % sure but that's how I got it =]
I hope I helped :)
wellllllllllllll doneeeeeeeeee babe.... :D :D :D :D
I love the way you convince me ;)
thnxs alot
Post by: The Golden Girl =D on December 11, 2011, 06:59:27 pm
La Shukra 3ala wajib =D
Post by: ~ Miss Relina ~ on December 12, 2011, 05:18:58 pm
that's a NMR question
why do we get 4 peaks only for that ''C6H5CH2CH2CH3 ????
if you are going to answer because peak for ch2 ,peak for second ch2 , peak for ch3 ,peak for c6h5
then I don't understant why are the five hydrogen atoms in benzene ring are the same ????
??? ??? ???
as it's opposing this example of 3 peaks for product of cyclohexene and bromine
Post by: NotAbod on December 12, 2011, 05:26:15 pm
Post by: ~ Miss Relina ~ on December 12, 2011, 05:27:39 pm
which unit is it? from which year?
I dunno it's from examwizard
did you get it ??? ::)
Post by: NotAbod on December 12, 2011, 05:29:20 pm
Is it related to the mass spectrometer?
Post by: ~ Miss Relina ~ on December 12, 2011, 05:30:39 pm
what 4 peaks? ::)edited NMR
Is it related to the mass spectrometer?
Post by: NotAbod on December 12, 2011, 05:32:37 pm
Post by: ~ Miss Relina ~ on December 12, 2011, 05:33:38 pm
Sorry, don't know what's that, its not unit 1.
ooopsss
no problem waiting for others :-\
Post by: Malak on December 12, 2011, 08:08:54 pm
guys here is my question and plz do explain it as I'm totally confused :'( :'(Not sure if i understood your question exactly but will try to explain.
that's a NMR question
why do we get 4 peaks only for that ''C6H5CH2CH2CH3 ????
if you are going to answer because peak for ch2 ,peak for second ch2 , peak for ch3 ,peak for c6h5
then I don't understant why are the five hydrogen atoms in benzene ring are the same ????
??? ??? ???
as it's opposing this example of 3 peaks for product of cyclohexene and bromine
Peaks appear on NMR cause of the different environments of H
Not sure about the benzene part (structure) but i guess because the five H atoms are in the same environment i.e. next to same groups
''C6H5CH2CH2CH"
In the case above, the last CH is next to 2 H so it will have its own peak (triplet)
the CH2 has one H on one side and 2H on the other so it has different environment and therefore a different peak
the last CH2 has C6H5 next to it and CH2 next to it so again a different environment
Hope you get it..
Post by: ~ Miss Relina ~ on December 12, 2011, 08:13:23 pm
guys here is my question and plz do explain it as I'm totally confused :'( :'(
that's a NMR question
why do we get 4 peaks only for that ''C6H5CH2CH2CH3 ????
if you are going to answer because peak for ch2 ,peak for second ch2 , peak for ch3 ,peak for c6h5
then I don't understant why are the five hydrogen atoms in benzene ring are the same ????
??? ??? ???
here can you explain this also plz
as it's opposing this example of 3 peaks for product of cyclohexene and bromine
???
Post by: The Golden Girl =D on December 12, 2011, 08:37:43 pm
The CH3 is next to a CH2 (according to the diagram it's blue in the sketch I did) and hence n+1 means that it's a Triplet.
the last CH is next to 2 H so it will have its own peak (n+1 => triplet)
so triplet and triplet , same environment and hence it's considered as One peak ?
this is PURE ta5bees I guess , but well this might be a possibility who knows :P
[ Don't ask me how I got it since ana mu5i darab min 2asasu fa I don't think I'll remember lol ]
Post by: ~ Miss Relina ~ on December 12, 2011, 09:10:45 pm
I hope this diagram explains it.
The CH3 is next to a CH2 (according to the diagram it's blue in the sketch I did) and hence n+1 means that it's a Triplet.
the last CH is next to 2 H so it will have its own peak (n+1 => triplet)
so triplet and triplet , same environment and hence it's considered as One peak ?
this is PURE ta5bees I guess , but well this might be a possibility who knows :P
[ Don't ask me how I got it since ana mu5i darab min 2asasu fa I don't think I'll remember lol ]
ok ta5bees msh wa7esh
bas I need to get that bold line
Post by: The Golden Girl =D on December 12, 2011, 09:19:49 pm
In the attached diagram. the CH2 is attached to TWO CH3. SAME Hydrogen Environment and hence considered as ONE Peak.
I took this idea and tried to Fit it in the one you were confused about.
This is all I can come up with I hope you get it =]
[ I need to study for tomorrow's test so Good Night =D ]
Post by: ~ Miss Relina ~ on December 12, 2011, 09:26:23 pm
can you confirm this plz green line
Post by: The Golden Girl =D on December 12, 2011, 09:28:49 pm
EDIT:
I labelled them 1 to 4.
Number 4 is Triplet and Number 3 is a Triplet.
# 4 cuz CH next to CH2 , n+ 1= 2+1= 3 hence triplet
# 3 cuz CH3 next to CH2 , n+ 1= 2+1= 3 hence triplet
I always hesitate fa ya3ni sorry cuz I might've confused you more =[
Post by: ~ Miss Relina ~ on December 12, 2011, 09:31:36 pm
I think I'll fail nmr ............ ::) confusing and hard :-\
Post by: ~ Miss Relina ~ on December 12, 2011, 09:32:17 pm
ONe second!
heheh......what ??? ::)
Post by: The Golden Girl =D on December 12, 2011, 09:34:59 pm
Post by: ~ Miss Relina ~ on December 12, 2011, 09:37:58 pm
I editted it ,co chck it please =]
I'll confuse you more and tell you that '' the CH group should be C only as it's a benzene ring what do u think ???
ya Allah be with us :(
also does two triplets have the same chemical shift I mean it just gives a hint on the adjacent hydrogen atoms ohhhhhhhhhhhhhhhh .........kan Allah fi el 3on
Post by: The Golden Girl =D on December 12, 2011, 09:40:25 pm
C is next to NO Carbon with a Hydrogen group except for Ch2 ,sa7 ? so it's a triplet 2+1 = 3
=]
Post by: ~ Miss Relina ~ on December 12, 2011, 09:42:10 pm
I'll confuse you more and tell you that '' the CH group should be C only as it's a benzene ring what do u think ???
ya Allah be with us :(
also does two triplets have the same chemical shift I mean it just gives a hint on the adjacent hydrogen atoms ohhhhhhhhhhhhhhhh .........kan Allah fi el 3on
editted
Post by: The Golden Girl =D on December 12, 2011, 09:57:02 pm
I'm sorry bas mu5i dareeb fa sorry 3al confusion 2ili 3amaltileek 2eeaha.
Good night Take care =]
Post by: ~ Miss Relina ~ on December 12, 2011, 09:59:19 pm
check this : http://www.youtube.com/watch?v=Oj-yxbPz5Ao but skip the beginning =]
I'm sorry bas mu5i dareeb fa sorry 3al confusion 2ili 3amaltileek 2eeaha.
Good night Take care =]
goodnoght Jazaki Allah Kairan :)
Post by: The Golden Girl =D on December 12, 2011, 10:00:42 pm
salam.
Post by: SZM on December 13, 2011, 11:52:55 am
1. Carbon consists of the isotopes 12C, 13C and 14C. Chlorine consists of the isotopes 35Cl and 37Cl. Use this data to calculate the maximum relative molecular mass of a molecule of carbon tetrachloride, CCl4
2. State the type of bond present in solid Sodium?? i think it is metallic bonding. Am i correct??
3. Write the equation for the process occurring when the second ionisation energy of oxygen is measured?? How can we write the equation??
OXYGEN is belonged to non-metal. Ok. So oxygen gains 2 electrons to form O2-. Am i right. So the energy needed to gain is called electron affinity// ow come ionisation energy is needed for oxygen??? cnt understand.. pls cn someone explain me clearly in details..
4. Why mass spectrometer always work with positive ions not negative ions??? if u say cant. why cant?? we cnt always accept the theory without reason. then we are said to be foolish by accepting their theory without reason. If u know the reason, pls tel me. it would be great help.
5. the graph shows the first seven successive ionisation energies of an element X, which is in Period 3 of the Periodic Table.
in graph, the y-axis is IONISATION ENERGY/ KJmol-1 and the x-axis is NUMBER OF THE ELECTRON REMOVED. It shows an increase rate from the first to the fourth and small slight change of increasing from 4th to 5th and small slight change of increasing from 5th to 6th. But there is a huge jump from 6th to7th.
the questions are-
1. use the information on the graph to state in which GROUP of the Periodic table X is found. Justify your answer.
2. identify the element X
3. The mass spectrum of X shows a singly charged molecular ion at m/e = 256. Write the formula of this ion.
pls cn someone answer those questions above clearly in details, so that i will be able to understand much better.
pls reply to my doubts asap.
Post by: Master_Key on December 13, 2011, 12:17:51 pm
hey folk, i cm across some doubts.1. RFM = (14*1) + (37*4)
1. Carbon consists of the isotopes 12C, 13C and 14C. Chlorine consists of the isotopes 35Cl and 37Cl. Use this data to calculate the maximum relative molecular mass of a molecule of carbon tetrachloride, CCl4
2. State the type of bond present in solid Sodium?? i think it is metallic bonding. Am i correct??
3. Write the equation for the process occurring when the second ionisation energy of oxygen is measured?? How can we write the equation??
OXYGEN is belonged to non-metal. Ok. So oxygen gains 2 electrons to form O2-. Am i right. So the energy needed to gain is called electron affinity// ow come ionisation energy is needed for oxygen??? cnt understand.. pls cn someone explain me clearly in details..
4. Why mass spectrometer always work with positive ions not negative ions??? if u say cant. why cant?? we cnt always accept the theory without reason. then we are said to be foolish by accepting their theory without reason. If u know the reason, pls tel me. it would be great help.
5. the graph shows the first seven successive ionisation energies of an element X, which is in Period 3 of the Periodic Table.
in graph, the y-axis is IONISATION ENERGY/ KJmol-1 and the x-axis is NUMBER OF THE ELECTRON REMOVED. It shows an increase rate from the first to the fourth and small slight change of increasing from 4th to 5th and small slight change of increasing from 5th to 6th. But there is a huge jump from 6th to7th.
the questions are-
1. use the information on the graph to state in which GROUP of the Periodic table X is found. Justify your answer.
2. identify the element X
3. The mass spectrum of X shows a singly charged molecular ion at m/e = 256. Write the formula of this ion.
pls cn someone answer those questions above clearly in details, so that i will be able to understand much better.
pls reply to my doubts asap.
2. Metallic
3. Ionization Energy --> yes.
Oxygen has 8 electrons. Measure the amount of energy required to remove the 7th electron after removing the 8th electon.
O+ --> O2+ + Ionization energy(2)
Post by: dk bose on December 13, 2011, 01:24:41 pm
OR
In the mass spectrometer, the sample is blasted with high energy electrons.this knocks electrons from the atoms in the sample.As protons(+) balance out electrons(-) in an atom.When one or more,electrons is knocked off an atom the protons now outnumber the electrons,therefore the ion formed is positively charged.
Post by: SZM on December 13, 2011, 02:32:12 pm
Post by: -Cornea on December 18, 2011, 02:02:12 pm
Post by: The Golden Girl =D on December 18, 2011, 02:20:44 pm
https://studentforums.biz/sciences-149/edexcel-chemistry-doubts!!!!/msg376298/?topicseen#msg376298 (https://studentforums.biz/sciences-149/edexcel-chemistry-doubts!!!!/msg376298/?topicseen#msg376298)
Post by: dk bose on December 21, 2011, 02:26:40 pm
hey,people!! could anyone try to solve my this doubt???the question is as follows-
(a)Aluminium is extracted by electrolysis of Al2O3.What is the maximum mass of the metal that could be obtained from 1 tonne of the oxide?
(b)If the yield of the electrolysis plant is 90%,what mass of the oxide must be used to produce 1 tonne of aluminium?
is there no one be able to answer my this question?its from the Edexcel AS chemistry revision guide.1st chapter,practice exam questions section. is there no specific teacher here to answer my doubts??
Post by: Romeesa-Chan on December 21, 2011, 02:42:42 pm
is there no one be able to answer my this question?its from the Edexcel AS chemistry revision guide.1st chapter,practice exam questions section. is there no specific teacher here to answer my doubts??Extraction of Aluminium is not in the portion. :-\
Post by: The Golden Girl =D on December 21, 2011, 05:50:28 pm
Please explain in Detail.
Thanks in Advance =]
Post by: Romeesa-Chan on December 21, 2011, 05:56:52 pm
is Water Polar ?Yes, it's polar.
Please explain in Detail.
Thanks in Advance =]
The electrons spend more time orbiting the oxygen nucleus than orbiting the two hydrogen nuclei, leaving the oxygen more negatively charged and the hydrogen more positively charge. Therefore, the entire molecule is "Polar", that is with one end slightly positive and one end slightly negative.
The two ends of these polar molecules can attract one another (positive to negative).
Post by: The Golden Girl =D on December 21, 2011, 06:03:31 pm
Post by: Romeesa-Chan on December 21, 2011, 06:18:12 pm
Jazaki Allah khair hun <3JazakAllah khairon.
Good luck, sis. (:
Post by: The Golden Girl =D on December 21, 2011, 06:23:28 pm
(I asked cuz whale and SZM wanted to know :) )
Post by: Romeesa-Chan on December 21, 2011, 06:28:06 pm
you too ;)Alright. I hope they got it now. :D
(I asked cuz whale and SZM wanted to know :) )
Post by: dk bose on December 21, 2011, 10:51:57 pm
Extraction of Aluminium is not in the portion. :-\
Didnt you read the question properly,its not abt extraction of aluminium.its about reacting masses,i find it really hard,if u can plzz solve it!!!
Post by: The Golden Girl =D on December 22, 2011, 01:10:52 pm
Post by: ~ Miss Relina ~ on December 23, 2011, 10:44:16 am
Post by: SZM on December 24, 2011, 05:27:56 am
I saw ur reply about whether the water is said to be a polar molecule or not.. Actually Golden Girl has posted this question here, because as she said, that Whale and I was arguing about this case through chatroom. He doesnt agree of why water molecule is said to be a polar.
My dear so far I agree, that-
1. water molecule is a polar molecule. But in biology we never say water molecule is a polar molecule ONLY. we say water is said to be a dipolar molecule. Am i correct?? The reason is because under the structure of a water molecule, it has one oxygen atom and two hydrogen atoms. One Oxygen atom has slightly negatively charged at its end and TWO not one hydrogen atoms have slightly positively charged at its end.
WE CALLED WATER IS SAID TO BE A DIPOLAR MOLECULE, because under the structure of water molecule, it has two oppositely charged from oxygen to hydrogen ions in left side as well as right side/. Because of two sides, we consider that they have two oppositely charged ions and therefore we called them a dipolar molecule. AM I CORRECT??? if I am wrong, pls correct me..
2. Oxygen atom has slightly negatively charged at its end and two hydrogen atoms have slightly positively charged at its end// But my question is, how oxygen atom became slightly negatively charged and hydrogen atom became slightly positively charged? The reason that I know so far is, because oxygen atom is said to be the highest electronegative element, which is electron lover. That means oxygen atom has its capability to pull the SHARED ELECTRON towards its nucleus away from hydrogen atom. AM i correct. That means I want to know who is pulling the SHARED ELECTRON?? so far I know to pull, it should be unlike charges in the form of attraction. So i thought the protons in the nucleus of an oxygen atom which has positively charged, is the one who pulls the shared electron, which is negatively charged, away from hydrogen atom. BECAUSE of pulling, the oxygen atom is going to gain a new electron , therefore it has become slightly negatively charged at its end, whereas the hydrogen atom is going to lose an electron, so therefore it has become slightly positive charged at its end, by obeying the octet rule of each atom.
I cannot agree , that the oxygen atom has become slightly negatively charged at its end and the hydrogen atom has become slightly positively charged at its end due to in terms of lone pairs./// LONE PAIRS do not do any effect on that, it does in other effect, which brought about different shapes and different value for bond angle from tetrahedron shape to angular bent shape. In oxygen atom , it has 2 lone pairs meaning 4 electrons as well as non-bonding electrons, whereas in hydrogen atom , it has no lone pairs, but it has bonding pairs of electron on one side as well as on other side. Why does it has effect on that, so far I know is, because of the repulsion, the distance between like charges which is lone pair to lone pair. NOT THE DISTANCE BETWEEN LONE PAIR TO THE NUCLEUS OF OXYGEN ATOM- (attraction). So the strength of the repulsion between lone pair to lone pair is greater than the strength of repulsion between lone pair to bond pair and bond pair to bond pair. Therefore new shape of water molecule is arranged in such a way to minimize the repulsion.
hope I hve answered my doubtful well. Pls correct me, if I am wrong. Then i can learn mistakes from u. Pls reply to me urgently.
waitn 4 ur reply asap.
wasalaam.
Post by: Malak on December 24, 2011, 03:33:37 pm
A molecule is polar if it has an overall charge i.e. the charge on the individual bonds do not cancel out.
You are confusing two terms, dipolar = dipoles and polarity is a different thing.
Water has a dipole nature i.e. seperation of charges which results in the water molecule being polar.
No where does the book says that water is not polar but dipolar.
2 - Well, I am just going to explain everything cause your question is very confusing :s
First of all, Oxygen is NOT the highest electronegative atom, it is Flourine.
Electronegativity is a measure of the attraction its atom has for a pair of electrons in a covalent bond.
Oxygen is more electronegative than Hydrogen therefore it will have greater attraction for the electrons in the covalent bond.
Just think about it,
Example, A neutral element like Chlorine (Cl). What will be the charge if it gains an electron? It will be negative.
Oxygen will therefore become slightly negative as the electron are more towards oxygen (it doesnt become negative, it will just have a dipole due to seperation of charges).
Hydrogen therefore becomes positive charge because electrons are away from it.
No one ever mentioned lone pairs, you are again confusing 2 things. Lone pairs determine the shape of the molecule.
Post by: Romeesa-Chan on December 24, 2011, 03:46:39 pm
1 -Agreed. (:
A molecule is polar if it has an overall charge i.e. the charge on the individual bonds do not cancel out.
You are confusing two terms, dipolar = dipoles and polarity is a different thing.
Water has a dipole nature i.e. seperation of charges which results in the water molecule being polar.
No where does the book says that water is not polar but dipolar.
2 - Well, I am just going to explain everything cause your question is very confusing :s
First of all, Oxygen is NOT the highest electronegative atom, it is Flourine.
Electronegativity is a measure of the attraction its atom has for a pair of electrons in a covalent bond.
Oxygen is more electronegative than Hydrogen therefore it will have greater attraction for the electrons in the covalent bond.
Just think about it,
Example, A neutral element like Chlorine (Cl). What will be the charge if it gains an electron? It will be negative.
Oxygen will therefore become slightly negative as the electron are more towards oxygen (it doesnt become negative, it will just have a dipole due to seperation of charges).
Hydrogen therefore becomes positive charge because electrons are away from it.
No one ever mentioned lone pairs, you are again confusing 2 things. Lone pairs determine the shape of the molecule.
Post by: SZM on December 24, 2011, 03:59:33 pm
may I know whether u have done Edexcel AS and A2 units both for Chemistry and Biology in exam??? Because whatever u r telling, some parts I agree, some parts i dont.
Because my teacher has explained to me in different ideas. Comparing ur ideas and my teacher ideas are not similar, because some parts i cannot agree , that means some parts i still didnt get what u mean//
could u please explain much more clear in details. Pleasssse.... Explain in a beautiful way ,so that i can understand much better. Please dont write short form . Write proper English. Sometimes I dont understand if u write in short form.
Please explain much more clear in step by step. Pls mention while you are explaining, that i should not say or write like this. please mentioned it, so that i will learn, what are the mistakes I have done and what are the concepts or ideas , I have misunderstood.
Please. I need your reply urgently..
Wasalaam
Post by: ~ Miss Relina ~ on December 24, 2011, 04:34:32 pm
Ang3l is right.....her way is simple and clear I don't find any confusion ....... :D
I prefer you search any websites to ensure that ???
Post by: ~ Miss Relina ~ on December 24, 2011, 04:35:31 pm
^SZM
Ang3l is right.....her way is simple and clear I don't find any confusion ....... :D
I prefer you search any websites to ensure your doubt ???
and to other guys plz if you are able to do it inform me plz :-\
Post by: Mike Benn on December 28, 2011, 05:48:53 am
Actually my question is regarding the last chapter NMR and Chromatography Unit 4., i just have to ask for some notes on these topics if anyone is having as the book ( George Facer ) lacks some points.
Will be Grateful if helped
Post by: KJ1995 on December 29, 2011, 04:34:07 pm
Thank you :)
Post by: KJ1995 on December 29, 2011, 04:39:45 pm
Salam alikum Everyone.,This should be heplful, credit go to the person i got it from, i think from this forums :)
Actually my question is regarding the last chapter NMR and Chromatography Unit 4., i just have to ask for some notes on these topics if anyone is having as the book ( George Facer ) lacks some points.
Will be Grateful if helped
Post by: KJ1995 on December 29, 2011, 05:18:16 pm
THANKS IN ADVANCE :DDDD
Post by: Deadly_king on December 29, 2011, 05:32:39 pm
I also want to ask, how should i know which technique to use when measuring the rate of reaction..it can be confusing because for example: If bromoethane reacts with hydroxide ions, electrical conductivity method can be used thats whats in the book and i agree, however a similar multiple choice question in one of the papers was the hydrolysis of bromobutane with hydroxide ions.. and i hat to choose the best method, i chose electrical which i think it works but the answer was titration with acid..I want to know when to use whats best in any situation.
THANKS IN ADVANCE :DDDD
Your answer lies in you own post :P
The book said that electrical conductivity method CAN be used ;) However it never mentionned that this was the best method ;)
In any case where an acid and a base are involved, titration is best since it is most accurate and less expensive as well as less risky ;)
Hope it helps :D
Post by: KJ1995 on December 29, 2011, 05:42:36 pm
Your answer lies in you own post :P
The book said that electrical conductivity method CAN be used ;) However it never mentionned that this was the best method ;)
In any case where an acid and a base are involved, titration is best since it is most accurate and less expensive as well as less risky ;)
Hope it helps :D
Thank you very much, i just want to maek sure of something.. you said in any case were acid and base are used i should use titration method, but here not both are acids and base, only the hydroxide ion is the base. Or do u mean when there is an acid OR base i should use titration method?
Post by: Deadly_king on December 29, 2011, 05:59:04 pm
Thank you very much, i just want to maek sure of something.. you said in any case were acid and base are used i should use titration method, but here not both are acids and base, only the hydroxide ion is the base. Or do u mean when there is an acid OR base i should use titration method?
Anytime :)
Yeah, you got it right ;)
Whenever there is an acid OR a base involved, it is best to use titration method ;)
Post by: ~ Miss Relina ~ on December 29, 2011, 06:05:53 pm
This should be heplful, credit go to the person i got it from, i think from this forums :)
wow ............really it's very helpful ;)
Thanks alot pal ;D
Have you got notes similar to that one for unit 5 ??? I wonder if you can post it soon plz :-\
Post by: ~ Miss Relina ~ on December 29, 2011, 06:08:59 pm
I need anywebsites that help wiyh that point asked by the syllabus
here it is :
. explain why the development of new catalysts is a priority area for chemical research today and, in this context, explain how the scientific community reports and validates new discoveries and explanations, eg the development of new catalysts for making ethanoic acid from methanol and carbon monoxide with a high atom economy (green chemistry)
Thanks in advance :)
Post by: Malak on December 29, 2011, 06:17:39 pm
i dont agree completely with what angl31 said.I have done AS chemistry and I am doing A2.
may I know whether u have done Edexcel AS and A2 units both for Chemistry and Biology in exam??? Because whatever u r telling, some parts I agree, some parts i dont.
Because my teacher has explained to me in different ideas. Comparing ur ideas and my teacher ideas are not similar, because some parts i cannot agree , that means some parts i still didnt get what u mean//
could u please explain much more clear in details. Pleasssse.... Explain in a beautiful way ,so that i can understand much better. Please dont write short form . Write proper English. Sometimes I dont understand if u write in short form.
Please explain much more clear in step by step. Pls mention while you are explaining, that i should not say or write like this. please mentioned it, so that i will learn, what are the mistakes I have done and what are the concepts or ideas , I have misunderstood.
Please. I need your reply urgently..
Wasalaam
Can you explain me in a better way, what did you not understand?Just saying that you didn't is too vague for me to reply.
By the way, I haven't used any short forms in my answer and I think my english was quite proper as others understood it.
Post by: KJ1995 on December 29, 2011, 06:20:40 pm
Anytime :)Thanks :D
Yeah, you got it right ;)
Whenever there is an acid OR a base involved, it is best to use titration method ;)
Post by: KJ1995 on December 29, 2011, 06:24:38 pm
wow ............really it's very helpful ;)
Thanks alot pal ;D
Have you got notes similar to that one for unit 5 ??? I wonder if you can post it soon plz :-\
Anytime ;)
Unfortunately, i dont have the unit 5 notes, didnt look for them since im doing u4 only in jan.. Sorry :/
Post by: KJ1995 on December 29, 2011, 06:40:43 pm
Post by: Assi1993 on December 31, 2011, 01:12:19 pm
8. A gaseous organic compound, X, was burnt in an excess of oxygen. A 0.112 dm sample of X, measured at s.t.p., produced 0.88 g of carbon dioxide.
How many carbon atoms are there in one molecule of X?
waiting
thankuuuu SF
Post by: Romeesa-Chan on December 31, 2011, 01:40:24 pm
heelloo frieds can anyone pleasseeeeee solve this question today?? its urgent..
8. A gaseous organic compound, X, was burnt in an excess of oxygen. A 0.112 dm sample of X, measured at s.t.p., produced 0.88 g of carbon dioxide.
How many carbon atoms are there in one molecule of X?
waiting
thankuuuu SF
-Noting that 1 mole of CO2 has 1 mole of Carbon,
use molar mass to find moles of carbon present:
( 0.88 g CO2 ) ( 1 mol Carbon / 44.01 g / ml CO2) = 0.02 moles of carbon
-Use the molar volume of gases at STP, to find moles of compound:
(A 0.112 dm^3) ( 1 mole of gas @STP / 22.4 dm^3) = 0.005 moles of compound
-Find how many moles of carbon in 1 mole of compound:
0.02 moles of carbon / 0.005 moles of compound = 4 moles of Carbon / mole compound
-If so, then there are 4 atoms of Carbon in 1 molecule of compound.
Credit goes to original poster. (: (http://answers.yahoo.com/question/index?qid=20111006152018AAj7A6C)
Post by: Romeesa-Chan on December 31, 2011, 01:41:08 pm
Can anyone tell me what are internal assessment tasks? And how do they help? im doing u4 chem in janTask for what ? :-\
Post by: KJ1995 on December 31, 2011, 04:03:36 pm
Task for what ? :-\
I dont know.. They are like tasks for unit 4, i dont have them, and i dont know if they are important so im just asking :)
Thanks anyways
Post by: Romeesa-Chan on December 31, 2011, 04:05:28 pm
I dont know.. They are like tasks for unit 4, i dont have them, and i dont know if they are important so im just asking :)Just go through the syllabus properly when studying. (:
Thanks anyways
No problem. (:
Post by: KJ1995 on January 01, 2012, 12:28:47 am
HA(weak acid) is being titrated with NaOH(aq)..A titration curve is drawn, the end point was somewhere between 9.0 and 9.4 pH. So the question was to use the curve to find the pH of an aqueous of NaA. The answer was between 9.0 and 9.4. Can someone please explain why? Is there a rule or something?, and make sure that your explanation is not just for this question (i mean that if i encounter a similar question, i want to know how to solve it)
Thank you for your help :D
Post by: The Golden Girl =D on January 01, 2012, 03:02:22 am
I don't get how we come up with d]ii) ... and e]iii)
(Yes .. It's in OUR Edexcel Syllabus! )
Thanks in Advance =]
Post by: The Golden Girl =D on January 02, 2012, 09:20:05 am
Post by: Deadly_king on January 02, 2012, 10:47:32 am
AQA January 2007 Question 4 (Paper Attached Hopefully =])
I don't get how we come up with d]ii) ... and e]iii)
(Yes .. It's in OUR Edexcel Syllabus! )
Thanks in Advance =]
4.(d)[ii] Isomer L has 2 hydroxyl groups while pentane dioic acid has 2 carboxyl groups. THe polymerisation therefore is going to be between one hydroxyl amd ome carboxyl group. This is known as an Ester Linkage which is a condensation polymerisation.
This may hopefully help you understand. (http://www.materialsworldmodules.org/resources/polimarization/4-condensation.html)
4.(e)[iii] AM sorry but I've forgotten about NMR :(
However am pretty sure you should first identify the two peaks in question. Only then will you be able to find the answer ;)
Am sorry for not being able to clear your doubt :-\
Post by: Deadly_king on January 02, 2012, 11:01:19 am
Need help in this question please :)
HA(weak acid) is being titrated with NaOH(aq)..A titration curve is drawn, the end point was somewhere between 9.0 and 9.4 pH. So the question was to use the curve to find the pH of an aqueous of NaA. The answer was between 9.0 and 9.4. Can someone please explain why? Is there a rule or something?, and make sure that your explanation is not just for this question (i mean that if i encounter a similar question, i want to know how to solve it)
Thank you for your help :D
The end-point usually refers to the pH of the solution which results after titration ;) This is why the pH of NaA is between 9.0 and 9.4 just like that of your end-point ;)
I'll take an example:
Let's say you are titrating HCl with NaOH. The resulting solution is NaCl and H2O has pH 7. Have you ever wondered why is that so?
It's simple, all the H+ ions from HCl have been neutralised by OH- ions from NaOH. Therefore only NaCl remains which is a neutral solution. We can hence conclude that the end-point would definitely lie at pH 7. However depending on the concentrations of the acid or base, the end-point may alter ;)
Hope I've been helpful :)
Post by: KJ1995 on January 02, 2012, 11:53:54 am
Anyone =/Im not sure if im answering you fully but from what i know.. 2 peaks mean that C atom has an adjacent C atom what contains 1 hydrogen ( N:number of hydrogen atoms adjacent; N+1=Number of peaks) Now for the other its 4 peaks so 4 = N+1, N=3, so it there is a C atom with 3 hydrogens too.. Which means there is CH3 and CH.. Now i checked the markscheme, the answer was something like CH3(-)CH(O)..Im not sure but something like that..I dont why did they write it that way and i dont why is the oxygen there, if by any chance u figure out why, could u please tell me?
Hope I've helped ;)
Post by: KJ1995 on January 02, 2012, 12:21:02 pm
Post by: Deadly_king on January 02, 2012, 02:26:19 pm
CO2(aq) + H2O(l) <-reversible-> H+(aq) + HCO3–(aq).... Why is HCO3- a base?
Bases can also be defined as proton acceptors ;)
In this case, the base HCO3- is accepting H+ to give H2O and CO2
This is why it is known as a base ;)
Post by: ~ Miss Relina ~ on January 02, 2012, 02:37:17 pm
but won't it form H2CO3 instead of being more dissosiated :-\
well wait a sec............I figured it out
HCO3- has lost OH- group so considered a base that's what I think
;)
Post by: Deadly_king on January 02, 2012, 02:46:59 pm
well wait a sec............I figured it out
HCO3- has lost OH- group so considered a base that's what I think
;)
That's also right ;)
HCO3- is actually CO2 and OH-
Post by: KJ1995 on January 02, 2012, 05:27:41 pm
That's also right ;)
HCO3- is actually CO2 and OH-
I get it now..Thanks :D
Post by: ~ Miss Relina ~ on January 03, 2012, 07:16:46 am
I wanna ask about tose points and whether I really have to know specific practical procedures for them or not
eCarry out the reaction of phenol with bromine water and dilute nitric
acid and use these results to illustrate the activation of the benzene
ring
fDescribe and carry out, where appropriate (using butylamine and
phenylamine), reactions to investigate the typical behaviour of
primary amines. This will be limited to:
i characteristic smell
ii miscibility with water as a result of hydrogen bonding and
the alkaline nature of the resulting solution
iii formation of salts
iv complex ion formation with copper(II) ions
v treatment with ethanoyl chloride and halogenoalkanes, eg
making paracetamol.
I need reply plz don't just ignore me :'(
Post by: MKh on January 03, 2012, 12:09:18 pm
Do you have the Edexcel A2 chemistry Revision Guide? See how much u have to know from there.
Post by: ~ Miss Relina ~ on January 03, 2012, 12:34:35 pm
Relina, i think these specification points relate mostly to the practical qualitative assessement but are likely to be tested in the written paper too so know them well.
Do you have the Edexcel A2 chemistry Revision Guide? See how much u have to know from there.
revison guide I downloaded it from here i think
do u have any papers in JAN
Post by: ~ Miss Relina ~ on January 03, 2012, 12:37:05 pm
revison guide I downloaded it from here i think
do u have any papers in JAN
plz one more thing do I have to do an experiment to investigate the miscibility of amines in water or just undrstand the concept as they ask for describe and carry out ???
Post by: Romeesa-Chan on January 03, 2012, 03:26:12 pm
plz one more thing do I have to do an experiment to investigate the miscibility of amines in water or just undrstand the concept as they ask for describe and carry out ???Check it according to the syllabus. ;) But if I am not wrong, you only have to understand the concept well.
Post by: ~ Miss Relina ~ on January 03, 2012, 03:44:25 pm
plz who is giong to do unit 5 or for who have already done unit 5 ???
I wanna ask about tose points and whether I really have to know specific practical procedures for them or not
eCarry out the reaction of phenol with bromine water and dilute nitric
acid and use these results to illustrate the activation of the benzene
ring
fDescribe and carry out, where appropriate (using butylamine and
phenylamine), reactions to investigate the typical behaviour of
primary amines. This will be limited to:
i characteristic smell
ii miscibility with water as a result of hydrogen bonding and
the alkaline nature of the resulting solution
iii formation of salts
iv complex ion formation with copper(II) ions
v treatment with ethanoyl chloride and halogenoalkanes, eg
making paracetamol.
I need reply plz don't just ignore me :'(
that's how my syllabus ask
Post by: Romeesa-Chan on January 03, 2012, 04:25:51 pm
Post by: ~ Miss Relina ~ on January 03, 2012, 04:37:35 pm
You do not have to do the experiment. Just learn it.Thanks Dr.Romeesa-Chan ;D
Post by: Romeesa-Chan on January 03, 2012, 04:47:33 pm
Thanks Dr.Romeesa-Chan ;DMost welcome, patient. :P
Post by: MKh on January 04, 2012, 11:55:34 am
revison guide I downloaded it from here i think
do u have any papers in JAN
Yes, i m having exams this jan.
You do not have to carry out these reactions, only the Home centre candidates have to.
Post by: SZM on January 06, 2012, 03:04:59 pm
May I know what is the written practical code number for Chemistry Unit 3 and Unit 6?? I was confused, as there is 6CHO7 and 8CHO3, 6CHO8 and 8CHO6??? Which one?? I want written practical paper not THE PRACTICAL, WHERE I HAVE TO CARRY OUT THE PRACTICAL SKILLS IN THE LAB//
pls i need ur reply asap.
Post by: Romeesa-Chan on January 06, 2012, 03:06:14 pm
Only schools provide the lab sessions.
Post by: AS01 on January 09, 2012, 07:06:05 pm
by the way how come you know everything have you completed your A levels?
Post by: AS01 on January 12, 2012, 07:19:49 pm
i know there definition. but the way they ask in exam i am unable to recognise whether which is bond enthalpy and which one is not.
for example for the reaction given below
1/4CH4(g)=>1/4C(g)+H(g)
why is this the mean bond enthalpy of CH4 bond not CH4(g)=>C(g)+2H2(g)?
plz explain this in detail.
Post by: AS01 on January 12, 2012, 07:23:08 pm
following shows the number of iodine atoms in 0.025 g of I2?
The Avogadro constant is 6.02 × 1023 mol–1.
Why the answer is this:-
0.025/126.9*6.02*10^23
not 0.025/253.8*6.02*10^23?
Post by: Blizz_rb93 on January 13, 2012, 01:47:32 am
The human body contains around 0.025 g of iodine molecules, I2. Which of the
following shows the number of iodine atoms in 0.025 g of I2?
The Avogadro constant is 6.02 × 1023 mol–1.
Why the answer is this:-
0.025/126.9*6.02*10^23
not 0.025/253.8*6.02*10^23?
i was wondering the same thing :/
& i have smth also
this is from Jan 2011 unit 1
question 3:
The Avogadro constant is 6.0 x 10^23 mol-1. Therefore the numbers of atoms in 1 mol of carbon dioxide is :
why is the answer 1.8 x 10^24 and not 6.0 x 10^23 :/
Post by: Malak on January 13, 2012, 11:33:21 am
The human body contains around 0.025 g of iodine molecules, I2. Which of the
following shows the number of iodine atoms in 0.025 g of I2?
The Avogadro constant is 6.02 × 1023 mol–1.
Why the answer is this:-
0.025/126.9*6.02*10^23
not 0.025/253.8*6.02*10^23?
I suppose because the question asks for atoms of iodine and not molecules?
Post by: Deadly_king on January 13, 2012, 06:29:57 pm
I suppose because the question asks for atoms of iodine and not molecules?
Exactly ;)
Each I2 molecule consists of 2 Iodine atoms ;)
Post by: MKh on January 14, 2012, 11:39:07 am
Exactly ;)
Each I2 molecule consists of 2 Iodine atoms ;)
Hi, just wanted to ask if u have done A2 Chemistry? Have you got any resources to prepare for the preparation question of the international written alternative to practical paper?
Any useful tips r also welcome.
Thanks in advance.
Post by: The Golden Girl =D on January 14, 2012, 11:41:06 am
Post by: Deadly_king on January 14, 2012, 02:36:24 pm
Hi, just wanted to ask if u have done A2 Chemistry? Have you got any resources to prepare for the preparation question of the international written alternative to practical paper?
Any useful tips r also welcome.
Thanks in advance.
I have completed my A2 Chemistry a year ago so I may not remember everything , am afraid. And yeah, I did CIE, not EDEXCEL ;)
Am sorry I don't even know how your paper is especially the Alternative to Practicals for in my time I had done Practicals itself :-\
But you can ask any doubt and I'll try to help as much as I can Insha Allah :)
Thanks Miss Invisble ;)
Post by: MKh on January 14, 2012, 06:10:34 pm
Sure, INSHA ALLAH.
Post by: Malak on January 16, 2012, 08:07:10 pm
Q: Explain why primary and tertiary bromoalkanes are hydrolyssed by different mechanisms.
It is from June 2010 unit 4
Thanks
Post by: Deadly_king on January 17, 2012, 01:02:01 pm
Can anyone give me a better explaination for this question. I dont understand the markscheme :S
Q: Explain why primary and tertiary bromoalkanes are hydrolyssed by different mechanisms.
It is from June 2010 unit 4
Thanks
I had the same doubt some time ago :P
Check my thread (https://studentforums.biz/sciences-149/0rgnic-ch3mi$try/) :P
Post by: ~ Miss Relina ~ on January 17, 2012, 03:01:54 pm
I need to discuss it but cann't find anyone........so I just was wonderiing if anyone can inbox me or somethnig.... :-\
Post by: MKh on January 17, 2012, 03:57:36 pm
anyone sat unit 6 B exam ????
I need to discuss it but cann't find anyone........so I just was wonderiing if anyone can inbox me or somethnig.... :-\
I sat for the Chemistry unit 6b exam. How did urz go, dear?
Post by: Malak on January 17, 2012, 04:40:04 pm
Post by: Malak on January 17, 2012, 04:42:04 pm
I had the same doubt some time ago :PThat is not my question :S
Check my thread (https://studentforums.biz/sciences-149/0rgnic-ch3mi$try/) :P
I know by which mechanism they react but i can't explain why?
I have read the chemguide website too and I understand it but I can't write it/explain in some easy words ::)
Post by: MKh on January 17, 2012, 06:26:34 pm
That is not my question :S
I know by which mechanism they react but i can't explain why?
I have read the chemguide website too and I understand it but I can't write it/explain in some easy words ::)
Refer to the Edexcel A2 Chemistry Revision Guide. You might find what u r looking for over there.
Post by: The Golden Girl =D on January 18, 2012, 01:03:41 pm
EDIT :
There are TWO ways for you to approach this Question
Method ONE :
Primary Haloalkane , group around it is SMALL => hence easy to attack
tertiary Haloalkane , groups around it are Bulky/big => Hence difficult to attack
Method TWO :
primary NOT Stable [there is an intermidate formed with a C+]
tertiary => Stable , surrounded by electron donating alkyl groups
[don't know what he meant by Alkyl groups though :-\ ]
Please, Don't forget to Include me in Your Prayers =D
Post by: Malak on January 19, 2012, 02:03:44 pm
Can anyone do this question for me :S
I don't understand why the volume is 12.5 :s
Q20 a(v)
Another doubt:
Why does diluting a weak acid increase its degree of dissociation? :S
Post by: Malak on January 19, 2012, 08:21:38 pm
Trans-esterification is fine for me now
but ofcourse I have another doubt :P
(attached) How is it D :S
Thanks
Post by: Deadly_king on January 20, 2012, 12:42:34 pm
Plus the above,can any also make trans-esterfication clear for me:S
Trans-esterification is fine for me now
but ofcourse I have another doubt :P
(attached) How is it D :S
Thanks
Firstly let's look for compounds which have optical isomers, i.e chiral centres!
This leaves us with only option B and D since A and C can in no way show chirality!
Now we look for E-Z isomers, only D is right for B has two methyl groups attached to the carbon containing the double bond! So it cannot show E-Z isomers.
Hope it helps :)
Post by: KJ1995 on January 20, 2012, 01:08:47 pm
Thanks GG :DWhen we add water the system trys to oppose the change (chattliers principle) by using up the water added which shifts equilibrium to the right, which means more [H+] and [CH3COO-], and less [CH3COOH].. putting those new values in the (Ka) equation will make the value of Ka bigger...and i also dont know why is it 12.5, can you please tell em when you find out?
Can anyone do this question for me :S
I don't understand why the volume is 12.5 :s
Q20 a(v)
Another doubt:
Why does diluting a weak acid increase its degree of dissociation? :S
Thank you
Post by: ~ Miss Relina ~ on January 20, 2012, 01:15:49 pm
Plus the above,can any also make trans-esterfication clear for me:S
Trans-esterification is fine for me now
but ofcourse I have another doubt :P
(attached) How is it D :S
Thanks
I'm sorry for interfering but are there any links which helped you out in Trans-esterification point
Thanks in advance ???
Post by: Malak on January 20, 2012, 03:40:44 pm
I used the text-book and the edexcel revision guide.
I'm sorry for interfering but are there any links which helped you out in Trans-esterification point
Thanks in advance ???
I dont think we need to know very much about it and the revision guide gave me enough detail needed.
Post by: The Golden Girl =D on January 20, 2012, 05:18:24 pm
Okay from the First part of the Question we know that in the Titration 0.25 moldm-3 of NaOH and 0.125 moldm-3 of Ethanoic Acid !!
so What I did is I found the Ratio as follows => Acid : Base
0.125 : 0.25 divide by 0.125 for both
I get a Ratio of => 1 : 2
And from the part (v) we get to know that 25 cm3 of the ACID is USED UP !!! .. so to find the Volume at the End point (Where the salt/product is given indicating that the ACID is completely KILLED) is
1 : 2
25 : X
Cross multiply and You'll find that the Volume of the BASE is => 12.5 cm3
I simply used my common sense and it worked :D
if it doesn't work Use the formula from the CIE board (not in the syllabus) ;
(C1V1) acid = (C2V2)base.... and act smart ;D
Post by: Malak on January 20, 2012, 06:10:12 pm
Another doubt (attached)
Q18 part c (ii)
Why do we use the moles and not the concentration given :s
Post by: The Golden Girl =D on January 20, 2012, 06:43:25 pm
I hope I helped (:
Post by: ~ Miss Relina ~ on January 22, 2012, 08:04:02 pm
Post by: Malak on January 22, 2012, 08:08:15 pm
what is the PH of 0.5 moldm-3 ammonia solution given Kb= 1.8 x 10-5 ;)You dont need to know that.
I know the old papers have this but if you check the specification. I doesn't mention Kb anywhere
Post by: ~ Miss Relina ~ on January 23, 2012, 07:01:47 am
You dont need to know that.but I didn't see it in old pastpapers actually it is in the Edxecel chemistry blue book
I know the old papers have this but if you check the specification. I doesn't mention Kb anywhere
Post by: Malak on January 23, 2012, 08:04:03 am
but I didn't see it in old pastpapers actually it is in the Edxecel chemistry blue bookYeah, for some reason it is there and even I thought that we had to know it but then I checked the spec. and they only mention Ka, Kw, Pka, Pkw, pH thats it.
Post by: guMnam on January 24, 2012, 02:26:24 pm
Yeah, for some reason it is there and even I thought that we had to know it but then I checked the spec. and they only mention Ka, Kw, Pka, Pkw, pH thats it.the point is .. its the same thing.. just opposite .. knowing it is no big deal.
Post by: ~ Miss Relina ~ on January 25, 2012, 11:10:21 am
why is the splitting pattern for butan1-ol is 36531
from where do we get five splitting :o
Post by: The Golden Girl =D on January 25, 2012, 12:56:40 pm
Since it can be Oxidized then it's either primary or secondary Alcohol ,tertiary can NOT be oxidized remember ;)
Draw butanol ,the primary , the secondary versions of it [if you are having trouble doing that let me know I'll draw it bas mikasila for now :P ..u r right I'm lazy ::) :P )
if you look at the spectrum for X in part (b) of the Question. Counting them from the left to right ,they are five splittings.
Splitting one => the one with 6 lines lined up closely to each other
splitting two => the Single long line
splitting THREE => the ones with 5 lines lined up closely to each other
Splitting FOUR => those TWO parallel LONG lines
Splitting FIVE => the three lines , having the middle one the LONGEST among them
CH3CH2CH(OH)CH3
starting from the LHS :
The first CH3 => is a triplet which is the (one with three lines and the middle one the LONGEST among them ;) )
the CH2 => is a Pentate [search for the ones with FIVE lines closely lined up together) ...that's the one for it ;)
the CH => is a Sixtet [search for the ones with SIX lines closely lined up together ]
the OH => the single line ...cuz OH is ALWAYS a single line since it's a singlet By the way ;)
the LAST Ch3=> is a Doublet [ search for the one with ONLY TWO lines ]
I hope I helped (: [jawabt su2aleek ana willa kunt bas 2atfalsaf o.O ]
(gtg go my own way ::) ..cya good luck with tomorrow ;) )
Don't forget to include me in your prayers sis ;D
Post by: ~ Miss Relina ~ on January 25, 2012, 01:18:24 pm
It's not 36531 ... it's actually 3400 (according to my teacher that is :) ) which is the peak for the OH in an Alcohol ;D
Since it can be Oxidized then it's either primary or secondary Alcohol ,tertiary can NOT be oxidized remember ;)
Draw butanol ,the primary , the secondary versions of it [if you are having trouble doing that let me know I'll draw it bas mikasila for now :P ..u r right I'm lazy ::) :P )
if you look at the spectrum for X in part (b) of the Question. Counting them from the left to right ,they are five splittings.
Splitting one => the one with 6 lines lined up closely to each other
splitting two => the Single long line
splitting THREE => the ones with 5 lines lined up closely to each other
Splitting FOUR => those TWO parallel LONG lines
Splitting FIVE => the three lines , having the middle one the LONGEST among them
CH3CH2CH(OH)CH3
starting from the LHS :
The first CH3 => is a triplet which is the (one with three lines and the middle one the LONGEST among them ;) )
the CH2 => is a Pentate [search for the ones with FIVE lines closely lined up together) ...that's the one for it ;)
the CH => is a Sixtet [search for the ones with SIX lines closely lined up together ]
the OH => the single line ...cuz OH is ALWAYS a single line since it's a singlet By the way ;)
the LAST Ch3=> is a Doublet [ search for the one with ONLY TWO lines ]
I hope I helped (: [jawabt su2aleek ana willa kunt bas 2atfalsaf o.O ]
(gtg go my own way ::) ..cya good luck with tomorrow ;) )
Don't forget to include me in your prayers sis ;D
Thanks alot my sis but what confused me that if you looked at JUNE 2011 last question part (d)(ii)
I was wondering why in spectrum 2 we have septet splitting (that short one and fat too )and it ois not octet
I'll post drawing now as ana nashhhhhhhhhhheeeta geadn ;)
Post by: The Golden Girl =D on January 25, 2012, 01:21:56 pm
[Will EDIT this post to answer you , waiting for ur drawing ya Miss.Nasheeta :P ]
(will check this thread later , gtg for now =/ )
Post by: ~ Miss Relina ~ on January 25, 2012, 01:35:42 pm
I don't usually bother to draw cuz it doesn't attach min 2asassu ..Ohh the Irony -.- :Phere :(
[Will EDIT this post to answer you , waiting for ur drawing ya Miss.Nasheeta :P ]
(will check this thread later , gtg for now =/ )
I'm getting worried :( :( :(
Post by: The Golden Girl =D on January 25, 2012, 01:46:08 pm
here :(
I'm getting worried :( :( :(
La inshAllah 5eer , go make wudu and pray [alahumma 2inza3 min galbee 2il5awf wal8ala8 ] ...I made it up and it always works alhamdulilah =]
Here (hopefully attached)
Post by: The Golden Girl =D on January 25, 2012, 01:48:14 pm
n + 1 => 6 + 1 = 7 hence it's a septet and it has SEVEN lines ;)
EDIT :No idea why it's not nine =/
Post by: ~ Miss Relina ~ on January 25, 2012, 01:51:38 pm
Post by: The Golden Girl =D on January 25, 2012, 02:00:06 pm
I think you shouldn't be thinking about it TOO MUCH .. Because in both cases the CH has the highest numbers of lines closely lined up together ,so it doesn't make much of a difference ? =/
Can someone clear our doubts please (:
Thanks =D
EDIT :[ The Exam is tomorrow so it's pretty much really Urgent =/ ]
Post by: Malak on January 25, 2012, 02:40:47 pm
Post by: Malak on January 25, 2012, 02:50:36 pm
In june 2011, there is a single H (joined to the carbon with methyl group) and it is also next to 5 hydrogens but forms 7 peaks.
Is that your question?
First of all, my teacher always told us that when ever there are a lot of peak like these two above, it is due to the hydrogen(s) which are next to many hydrogens.
I think, in june 2011 it has 7 peaks because, don't forget, even though they hydrogens of methly group are not directly next to the single hydrogen but they do affect it and probably thats why it has 7 peaks.
In jan 2010, there is only a single H of OH which is not directly next to the 'single' hydrogen we are talking about and so it doesnt really have an impact.
------------------------------
By the way, do we have to know the mechanism between propane and iodine (the very complicated one) :-\
Post by: jackfos92 on January 30, 2012, 01:44:31 pm
it is complex ion. i needa know the colour!!! urgent!
Post by: The Golden Girl =D on February 20, 2012, 04:33:24 pm
Ladies and gentlemen can someone clear my doubt , got a test tomorrow -.-
Can someone state what a ligand exchange is and what an acid-base reaction is , what is the difference between them because I'm confused =/
Thanks (:
Post by: MKh on February 21, 2012, 11:00:21 am
To understand a ligand exchange reaction, u will have to understand what a ligand actually is.
Post by: The Golden Girl =D on February 25, 2012, 03:46:16 pm
Post by: Romeesa-Chan on February 25, 2012, 04:55:49 pm
^ I believe it is violet solution ..according to my chemistry knowledge *poker face*
Ladies and gentlemen can someone clear my doubt , got a test tomorrow -.-
Can someone state what a ligand exchange is and what an acid-base reaction is , what is the difference between them because I'm confused =/
Thanks (:
Ligand exchange reaction - is a reaction in which one ligand in a complex ion is replaced by a different one.
http://www.chemguide.co.uk/inorganic/complexions/ligandexch.html
Acid-Base reaction - is when the acid and base molecules destroy each other when mixed in the right proportions [neutralisation reaction].
Post by: The Golden Girl =D on February 27, 2012, 05:20:16 pm
Post by: mandy12 on March 04, 2012, 01:42:37 am
Post by: MKh on March 04, 2012, 12:42:06 pm
Can someone give me the revision for unit6b paper? i really don't know how to revise for that.. ???
The Chemistry laboratory skills II exam consists of 3 sections: qualitative analysis (identfying unknown compounds), quantitative analysis (calculations, graphs etc.) and Preparation (explaining the steps in a given experimental procedure for carrying out a preparation) of organic and inorganic compounds.
Check the Practical Assessment section in the Edexcel A2 Chemistry Revision Guide which is available for download in SF.
You will find very helpful information in that section. From the Revison Guide, I quote:
Qualitative analysis
Chemical reactions and tests that may be included in this section include:
- Any of those listed for Unit 3 (therefore you will also have to check the qualilative analysis section the Edexcel AS Chemistry Revision Guide)
- The reactions of the transition metal ions in solution with aqueous sodium hydroxide and with aqueous ammonia both added untl in excess (see pg 81 of guide)
- Ligand exchange reactions in copper (II) complexes (pg 79 of guide)
- The redox chemistry of chromium (pg 78 of guide)
[And the list goes on. It is better if you check the Guide itself]
Quantitative analysis
At least one of the following will be included in this assessment:
- pH titration
- Following the rate of a reaction
- Potassium manganate (VII) titration
- Finding the activation energy of a reaction
Preparation
Laboratory practices needed for preparation:
- Those developed at AS, such as heating under reflux and distillation
- Purification of an impure solid product by recrystallization from hot, saturated solvent
- Melting temperature determination
- Drying solid by filtration under reduced pressure - using a Buchner funnel and flask
Do make sure that you know how to draw labelled diagrams for the apparatus used to carry out distillation, reflux, filtration under reduced pressure and the ones used to determine melting and boiling temperature of a compound
Hope this helps.
Post by: SZM on March 26, 2012, 03:51:27 pm
can you tel me what is the difference between IN TERMS OF STRUCTURE AND BONDING in Iron (II) Chloride and Iron (III) chloride???
Please explain me clearly along with diagram...
Thanx in advance.
Post by: SZM on March 31, 2012, 08:04:11 pm
Post by: Romeesa-Chan on March 31, 2012, 08:12:04 pm
Hello guys,
can you tel me what is the difference between IN TERMS OF STRUCTURE AND BONDING in Iron (II) Chloride and Iron (III) chloride???
Please explain me clearly along with diagram...
Thanx in advance.
The question is clear itself.
It asks to differentiate Iron Chloride (II) and Iron Chloride (III) in terms of their bonding and the structure of the molecule.
Post by: SZM on March 31, 2012, 08:44:21 pm
The question is clear itself.
It asks to differentiate Iron Chloride (II) and Iron Chloride (III) in terms of their bonding and the structure of the molecule.
Sister Romeesa,
I want the answer for the difference between Iron (111) chloride and Iron (11) chloride??? i want the answer// So to explain this answer, pls ur answer shuld be in terms of their structure and bonding....
Hope u got my point. IN SHAA ALLAH.
Waiting 4 ur reply. Wasalaam.
Post by: NotAbod on April 03, 2012, 05:03:19 pm
Post by: Malak on April 05, 2012, 02:18:11 pm
Why can't aldehyde form hydrogen bond with another aldehyde?For hydrogen bonding to occur, Hydrogen should be bonded to N, F or O. In aldehydes, there is none of them. There is an oxygen but bonded to Carbon, not hydrogen.
Post by: NotAbod on April 05, 2012, 02:20:46 pm
Thanks ang3l
Post by: farhanyen on April 10, 2012, 02:38:50 pm
My A2 text book:
-dissolve theimure solid in aminimum of hot solvent
-remove any undissolved impurities by filtering the hot solution through a fluted filter paper using a warmed stemless funnel , into a conical flask.
-allow the solution to cool
-Filter the mixture of the pure solid and the solvent under reduced pressure, using a buchner funnel
Collect the solid on the filter paper and discard the filtrate which contains the soluble impurities
-Wash the solid on the filter paper and leave the solid to dry
-carefully remove the pure solid from the filter paper
Past Paper Question: Organic solids are often purified by recrystallisation.This technique waorks on the basis that...
Answer:the cooled solution is saturated with the desired material but not with the impurities
What i don't understand:My text book says that the desired compound is soluble in the hot solution bot not in the cooled solution . So how can the desired material be saturated in the cool solution?????
Post by: Romeesa-Chan on April 10, 2012, 02:52:21 pm
Question on recrystallisation
My A2 text book:
-dissolve theimure solid in aminimum of hot solvent
-remove any undissolved impurities by filtering the hot solution through a fluted filter paper using a warmed stemless funnel , into a conical flask.
-allow the solution to cool
-Filter the mixture of the pure solid and the solvent under reduced pressure, using a buchner funnel
Collect the solid on the filter paper and discard the filtrate which contains the soluble impurities
-Wash the solid on the filter paper and leave the solid to dry
-carefully remove the pure solid from the filter paper
Past Paper Question: Organic solids are often purified by recrystallisation.This technique waorks on the basis that...
Answer:the cooled solution is saturated with the desired material but not with the impurities
What i don't understand:My text book says that the desired compound is soluble in the hot solution bot not in the cooled solution . So how can the desired material be saturated in the cool solution?????
Read the 2nd and 3rd point of the textbook again.
-remove any undissolved impurities by filtering the hot solution through a fluted filter paper using a warmed stemless funnel , into a conical flask.
-allow the solution to cool
Hope it's clear now.
Post by: dk bose on April 17, 2012, 09:23:24 am
At 298K,the enthalpy change on dissolving is +19kj mol-1.
(a)Calculate the entropy change in the system
Post by: dk bose on April 17, 2012, 09:32:56 am
At 298K,the enthalpy change on dissolving is +19kj mol-1.
(a)Calculate the entropy change in the system
plzzzz solve this doubt and post the solutions as fast as possible...plzzz help me people!!!!!!
Post by: KJ1995 on May 01, 2012, 07:54:22 pm
How should i study Unit 6B chemistry. Are there any helpful books, please post the download links.. And what practicals should i know from AS and A2 for Unit 6B
Many thanks
Post by: MKh on May 03, 2012, 10:58:51 am
How should i study Unit 6B chemistry. Are there any helpful books, please post the download links.. And what practicals should i know from AS and A2 for Unit 6BThe Chemistry laboratory skills II exam consists of 3 sections: qualitative analysis (identfying unknown compounds), quantitative analysis (calculations, graphs etc.) and Preparation (explaining the steps in a given experimental procedure for carrying out a preparation) of organic and inorganic compounds.
Check the Practical Assessment section in the Edexcel A2 Chemistry Revision Guide which is available for download in here in SF - use the search engine to search for the download link.
You will find very helpful information in that section. From the Revison Guide, I quote:
Qualitative analysis
Chemical reactions and tests that may be included in this section include:
- Any of those listed for Unit 3 (therefore you will also have to check the qualilative analysis section of the Edexcel AS Chemistry Revision Guide which is also available for free download here in SF)
- The reactions of the transition metal ions in solution with aqueous sodium hydroxide and with aqueous ammonia both added untl in excess (see pg 81 of guide)
- Ligand exchange reactions in copper (II) complexes (pg 79 of guide)
- The redox chemistry of chromium (pg 78 of guide)
[And the list goes on. It is better if you check the Guide itself]
Quantitative analysis
At least one of the following will be included in this assessment:
- pH titration
- Following the rate of a reaction
- Potassium manganate (VII) titration
- Finding the activation energy of a reaction
Preparation
Laboratory practices needed for preparation:
- Those developed at AS, such as heating under reflux and distillation
- Purification of an impure solid product by recrystallization from hot, saturated solvent
- Melting temperature determination
- Drying solid by filtration under reduced pressure - using a Buchner funnel and flask
Do make sure that you know how to draw labelled diagrams for the apparatus used to carry out distillation, reflux, filtration under reduced pressure and the ones used to determine melting and boiling temperature of a compound
Hope this helps.
Post by: -Cornea on September 28, 2012, 02:02:35 pm
Post by: Deadly_king on September 28, 2012, 02:38:49 pm
is anyone over here doing AL chemistry if so i need a proof for bohr's theory of atomic structure it's not actually a proof it's the steps from where did we we get tht 109678 number ....Thanks in advance :)
It's just a constant which you need to use ;)
I doubt you need to know how it is obtained!
http://library.thinkquest.org/19662/low/eng/model-bohr.html
Post by: baditude on December 11, 2012, 04:41:38 pm
ASAP please, i've got an exam tomorrow.
Post by: Deadly_king on December 13, 2012, 02:04:19 pm
Can someone please help me with January 2010, unit 4 Question 26
ASAP please, i've got an exam tomorrow.
I don't have the paper :/
Can you post the question itself or provide a link to the paper?
Post by: Maheen.S on December 18, 2012, 07:35:25 pm
Post by: Za_shadow on December 31, 2012, 01:05:54 pm
jan 09 question 23 c i )
why did he multiply 2*0.01/2 *100
and didn't multiply 30*0.5/30 *100
jan 2010 Q5 why A i don't understand the question :(
and Q6 why A not C
May 2010 Q4 (a) why B ??????
May 2011 Q8 why C ???
and Q9 why C ???
really appreciate anyy helpp and thank u veryyyyy mucchhhh
Post by: Amelia on December 31, 2012, 03:05:25 pm
plzzzz helppp mee
jan 09 question 23 c i )
why did he multiply 2*0.01/2 *100
and didn't multiply 30*0.5/30 *100
jan 2010 Q5 why A i don't understand the question :(
and Q6 why A not C
May 2010 Q4 (a) why B ??????
May 2011 Q8 why C ???
and Q9 why C ???
really appreciate anyy helpp and thank u veryyyyy mucchhhh
I'm sorry, but can you post the links of the question paper or the questions itself? It will be easier to answer. Thank you and sorry.
Post by: Za_shadow on January 02, 2013, 02:14:34 pm
I'm sorry, but can you post the links of the question paper or the questions itself? It will be easier to answer. Thank you and sorry.
sure no problem at all but plzzz help me
http://www.edexcel.com/migrationdocuments/QP%20GCE%20Curriculum%202000/January%202009/6CH01_01_que_20090109.pdf
http://www.edexcel.com/migrationdocuments/QP%20GCE%20Curriculum%202000/GCE%20January%202010%20-%20QP/6CH01_01_que_20100114.pdf
http://www.edexcel.com/migrationdocuments/QP%20GCE%20Curriculum%202000/june2010-qp/6CH01_01_que_20100521.pdf
http://www.edexcel.com/migrationdocuments/QP%20GCE%20Curriculum%202000/June%202011%20-%20QP/6CH01_01_que_20110523.pdf
and thanks again
Post by: NotAbod on January 02, 2013, 03:50:45 pm
No idea about the rest, I suck at unit 1 Chemistry. :(
Post by: DrThamooth on May 10, 2013, 09:56:24 pm
I really need the CGP chemistry A2 guide
i cannot find it anywhere x_x
if any of you have the link maybe or you can upload it , it would really be appreciated ..
thank you :D
Post by: Amany ali on May 12, 2013, 06:11:00 am
Post by: Alaa Mounier on May 16, 2013, 04:12:53 pm
A- Aluminum is extracted by electrolysis of Al2O3. What is the maximum mass of the metal that could be obtained from 1 tonne of the oxide?
B- If the yield of the electrolysis plant is 90%. What mass of the oxide must be used to produce 1 tonne of aluminum? >:(
Post by: conquerpro on May 27, 2013, 08:56:13 am
Post by: Candiah on May 27, 2013, 08:01:18 pm
Ca + 2H20 -----> ca(OH)2 + H2
Post by: conquerpro on May 27, 2013, 08:11:44 pm
Post by: Candiah on May 27, 2013, 08:36:10 pm
s2O3-- + I2 ------> S4O6-- + 2 I-
so IO3- ie equivalent to 3 I2 equivalent to 3 S2O3--
moles of thiosulphate = 30 x 0.5/1000 = 15 x 10-3
moles of iodate = 15 x 10-3 /3 = 5 x 10-3
25 cm3 ===== 5 x 10 -3
1000 ======= 5 x 10-3 x 1000/25
0.2 mol dm-3
sorry about the upper and lower case I can't do them
sorry i don't know how to do upper and lower cases
Post by: conquerpro on May 28, 2013, 10:02:38 am
Post by: NotAbod on May 28, 2013, 10:11:45 am
Sorry, I forgot about it, been a year :/
Post by: conquerpro on May 28, 2013, 12:54:41 pm
Post by: Suryaw1 on May 28, 2013, 05:52:29 pm
For the half redox equation, give me a question. I will solve it and give the explanation.
Post by: daniel@mahsa.edu.my on May 29, 2013, 07:42:37 am
what is the oxidation state of ozone O3?
Hi. Dont worry.
Refresh your memeory: If its an element, the oxidation state is zero.
That helps knowing that oxidation state of P4, S8, O2, O3, Cl2, Br2, N2 as zero!
Good luck in your exams
Dan
Post by: conquerpro on May 29, 2013, 02:54:23 pm
a solid gives a red colour in a flame test and reacts with conc H2SO4 to produce steamy fumes,but no other gases.the solid could be
A.LiBr
B.SrCl2
C.CaCl2
D.NaCl
the answer is SrCl2.but as we know CaCl2 also gives a brick red colour with conc H2SO4.so why not CaCl2
Post by: DrThamooth on June 07, 2013, 12:09:13 pm
i need help in past papers x_x
june 2010 - Q19 a ii
i cannot solve it :/
Ethanoic acid can be manufactured by the following reaction, which is carried out
between 150 °C and 200 °C.
CH3OH(g) + CO(g) = CH3COOH(g)
(a) A mixture of 50.0 mol of methanol and 50.0 mol of carbon monoxide reaches
equilibrium at a pressure of 32.0 atm. At 175 °C, the equilibrium partial pressure of
ethanoic acid is 22.2 atm.
(ii) Calculate the partial pressures of methanol and carbon monoxide at equilibrium.
Post by: conquerpro on April 11, 2014, 05:42:19 pm
can someone plzz solve this MCQ for me and explain?
a sample of swimming pool water contains 0.482 ppm of chlorine.this is equal to a percentage of
A.0.000482
B.0.0000482
C.0.00000482
D.0.000000482
this is from edexcel chem 1
[/quote]
[/quote]
Post by: conquerpro on April 11, 2014, 05:51:47 pm
Post by: astarmathsandphysics on April 24, 2014, 02:12:49 pm
Post by: NotAbod on April 24, 2014, 08:55:51 pm
can someone PLZZZZ tell me what happens when zinc hydroxide reacts with H+ ions?cuz i know ZN(OH)2 is amphoteric and reacts with OH- ions to give ZN(OH)4 but what does it give when it reacts with H+ ions?Yes, water. You get salt too.
Post by: conquerpro on April 27, 2014, 08:35:52 am
Yes, water. You get salt too.
ya,but which salt would u get???
Post by: astarmathsandphysics on April 28, 2014, 09:04:56 pm
I don't know if this is a salt.
Post by: NotAbod on April 29, 2014, 10:37:27 am
If the acid is H3PO4, your salt is Zn3(PO4)2
By the way, is that an mcq?
Post by: conquerpro on April 30, 2014, 03:08:55 am
By the way i have another doubt.when 4 ligands attack a transition metal cation we know that the shape is either tetrahedral or square planar.but how do we know WHEN its square planar and when its tetrahedral?
Post by: NotAbod on April 30, 2014, 09:37:25 am
Post by: conquerpro on May 19, 2014, 01:38:32 pm