IGCSE/GCSE/O & A Level/IB/University Student Forum
Qualification => Subject Doubts => IGCSE/ GCSE => Sciences => Topic started by: elemis on August 23, 2010, 04:24:21 pm
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Before posting your IGCSE Chem doubts here, have a look in this thread (https://studentforums.biz/igcse-subjects-doubtshelp/chem-and-bio-help-and-tips-here/) and this one (https://studentforums.biz/igcse-subjects-doubtshelp/igcse-chemistry-doubts/). Also try this one (https://studentforums.biz/igcse-subjects-doubtshelp/all-doubts-here!/)
Some good Paper 3 notes over here. (https://studentforums.biz/igcse-subjects-doubtshelp/chemistry-p3-762010/)
Use the search function in that thread to see if your doubt has already been answered.
If it hasn't then post here and someone will help you.
Don't forget to mention the following;
1. The Year and session.
2. The Question number/part you have doubt in.
It would be better if you uploaded the paper by attaching it.
Check THIS (https://studentforums.biz/index.php?topic=10274.0) for Resources =D
Thank you =)
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helllo ppl
i have some questions on the mole concept.. can someone please help.
1)Consider the combustion of pentanol: 2C5H11OH + 15O2 ---> 10CO2 + 12H2O
(a) How many grams of carbon dioxide are formed for each mole oxygen consumed?
(b) How many grams of carbon dioxide are formed for each gram of pentanol burned?
2) What mass of iron (iii) oxide will be produced by the complete oxidation of iron?
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Do you have the answers? I just want to be sure my solutions are correct.
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Do you have the answers? I just want to be sure my solutions are correct.
yeah i do
1) (a) 29.3g
(b) 2.49g
2) 143g
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hello? percy jackson???
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Oh I'm really sorry. :-[ I'm afraid I don't know the 2nd one. :-[
1) a)
2C5H11OH + 15O2 ---> 10CO2 + 12H2O
Molecular mass of CO2 = 12 + 32
= 44 g
molar ratio of
CO2 : O2
15 : 10
1 : x
so, x = 10/15
Mass of CO2 = 10/15 * 44
= 29.3 g
b) Ratio of
pentanol : CO2
2 : 10
1 : x
so for 1 mole, x = 5
Therefore 1 mole of pentanol = 5 moles of CO2 is formed
= 44 * 5
= 220 g
Now, you gotta find for 1 gram of pentanol
Mass of pentanol = 60 + 11 + 16 + 1
= 88g.
So,
Pent. CO2
88g 220g
1g x
x = 220/88
= 2.5 g
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thanks alot for the detailed answer! :) as for no. 2 i'll try to figure it out ;)
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thanks alot for the detailed answer! :) as for no. 2 i'll try to figure it out ;)
You're welcome. Hope you got it. It's a bit crude. I'll ask my teacher too tmw. ;)
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yeah i do
2) 143g
Are you sure about the answer? Also is the question you know, complete?
It should be 80g according to me. :\
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2C5H11OH + 15O2 -----> 10CO2 + 12H2O
a) According to the equation :
15 moles of oxygen are required to produce 10 mole of carbon dioxide
15 moles of oxygen are required to produce (10 x44)g of carbon dioxide ( Mr of CO2 = 44)
Therefore 1 mole of oxygen will produce (10 x 44)/15 = 29.3g of CO2
b) According to the equation :
2 moles of pentanol burns to form 10 moles of carbon dioxide
(2 x 88)g of pentanol burns to form (10 x 44)g of carbon dioxide (Mr of pentanol = 83)
1g of pentanol will therefore burn to form (10 x 44) / (2 x 88) = 2.5g of CO2
2) 4Fe + 3O2 ----> 2Fe2O3
According to the equation :
For complete oxidation to take place, 4 moles of Fe reacts with 3 moles of O2 to form 2 moles of Fe2O3
1 mole of Fe reacts with 3/4 moles of O2 to form 1/2 moles of Fe2O3
1 mole of Fe reacts with 3/4 moles of O2 to form (1/2 x 159.6)g of Fe2O3
Mr of Fe2O3 = 159.6
Mass of iron (iii) oxide formed upon complete combustion of 1 mole of Fe = (159.6/2) = 79.8g
I agree with Percy.
Hey shooting star......u asked the same question here (https://studentforums.biz/sciences-149/chem-mole-calculation-plz-help/msg349416/#msg349416)
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i dont get chromotography at all :S
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i dont get chromotography at all :S
Hang on.
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http://www.docbrown.info/page04/OilProducts13.htm
Read carefully.
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http://www.docbrown.info/page01/ElCpdMix/EleCmdMix2.htm#Chromatography (http://www.docbrown.info/page01/ElCpdMix/EleCmdMix2.htm#Chromatography)
This also.
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Can someone please answer this for me... :)
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1 minute.
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12.04/23 = 0.5235
11.52/11 = 1.047
29.32/16 = 1.833
47.12/18 = 2.62
Dividing all the above numbers by the lowest number gives a ratio of : 1 : 2 : 4 : 5
Formula = NaB2O45(H2O)
hence answer is C
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For second one.
Its Ultraviolet rays, they cause sunburn.
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Thanks and +rep!!! ;)
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Ari or someone can you do this for me plz, I need to check my answers... ;)
By the way +rep will be given... ;)
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Thats going to be hardwork :P
I'll do question 1 :P
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please I really need them all... :(
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Nucleus has an overall +ve charge.
2
6
10
The spin will be in opposite directions i.e. one will spin anticlockwise and the other clockwise.
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Rutherford Experiment, right ? I'm sure you know this.... its in your textbook probably.
A surprise since 1 in 20000 alpha particles were deflected backwards causing scintillations.
Revised to include a nucleus which contains most of the mass of an atom; though this mass is concentrated in a VERY small area.
Ummm, I think Gold foil was used since gold is very malleable and could be made easily into a thin sheet of foil - remember Alpha particles have a very low penetration.
I guess exposure to radiation used in testing is the answer.
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No. 2 I did it correctly... so carry on to Q3. plz
By the way Thanks for helping...
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I have no idea of the answers to Question 3. I've just started my AS Level. SO forgive me :P
Question 6
a) http://www.periodictable.com/Elements/028/data.html (http://www.periodictable.com/Elements/028/data.html) Click on the elements at the top of the page to view the Electronic Config.
b) I dont understand what they are ak
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QUestion 5
(http://www.chemguide.co.uk/atoms/properties/energies.GIF)
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4 a) The amount of energy needed to remove an electron from one mole of an atom of a gaseous element.
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I have no idea of the answers to Question 3. I've just started my AS Level. SO forgive me :P
Question 6
a) http://www.periodictable.com/Elements/028/data.html (http://www.periodictable.com/Elements/028/data.html) Click on the elements at the top of the page to view the Electronic Config.
b) I dont understand what they are ak
For Question 6) b):
i) The 4s orbital will fill before a 3d orbital, because the 4s orbital is at a lower energy level than a 3d orbital. The order of filling orbitals based on their energy level is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, ...
ii) It is strange that the 4s orbital has not been completely filled up before moving on to the 3d orbital (which incidently is full - filled with 10 electrons). This is because copper is one of the exceptions to Hund's rule, where one of the 4s electrons moves into the last 3d orbital. This is known to be because there is more stability if it is arranged in this way - a full 3d subshell.
iii) Chromium is the other exception, arranged in a similar way - with having a half full 3d subshell, which appear to be associated with greater stability.
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For Question 6) b):
i) The 4s orbital will fill before a 3d orbital, because the 4s orbital is at a lower energy level than a 3d orbital. The order of filling orbitals based on their energy level is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, ...
ii) It is strange that the 4s orbital has not been completely filled up before moving on to the 3d orbital (which incidently is full - filled with 10 electrons). This is because copper is one of the exceptions to Hund's rule, where one of the 4s electrons moves into the last 3d orbital. This is known to be because there is more stability if it is arranged in this way - a full 3d subshell.
iii) Chromium is the other exception, arranged in a similar way - with having a half full 3d subshell, which appear to be associated with greater stability.
Hehe......this whole paper was already answered in another thread. ;)
Anyway thanks for the help :)
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Stop being a cynic man
Appreciate whatever help people give in any quantity from any source.
+Rep Ivo
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Stop being a cynic man
Appreciate whatever help people give in any quantity from any source.
+Rep Ivo
Hey am not being cynic......just wanted to let him know :D
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Can anyone tell me what are the main topics focused in chemistry paper 6? thank u
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Can anyone tell me what are the main topics focused in chemistry paper 6? thank u
Know the names of basic equipment.
Know ALL the tests and results for Anions and Cations.
Be prepared to describe the experimental procedure for a simple experiment - like a titration.
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Know the names of basic equipment.
Know ALL the tests and results for Anions and Cations.
Be prepared to describe the experimental procedure for a simple experiment - like a titration.
oh okay then
the apparatus i know and the tests and results for anions and cations but can you explain to me titration, i really dont understand the coencept, why do they use and which conditions are needed and etc
thank you
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http://www.echeat.com/essay.php?t=30794
Read it.
Got questions post here ;)
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Ammonium sulfate was prepared by adding ammonia solution to 25 cm3 of 2.0 mol dm-3 sulfuric acid.
2NH3(aq) + H2SO4(aq) --> (NH4)2SO4(aq)
Question:
i) What volume of 2.0 mol dm-3 ammonia solution will just neutralise the sulfuric acid? I got 50 cm3.
ii) How could you test to check that enough ammonia has been added to neutralise the sulfuric acid?
Thanks in advance!
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Ammonium sulfate was prepared by adding ammonia solution to 25 cm3 of 2.0 mol dm-3 sulfuric acid.
2NH3(aq) + H2SO4(aq) --> (NH4)2SO4(aq)
Question:
i) What volume of 2.0 mol dm-3 ammonia solution will just neutralise the sulfuric acid? I got 50 cm3.
ii) How could you test to check that enough ammonia has been added to neutralise the sulfuric acid?
Thanks in advance!
i got 50 cm3 too
ii)test with and indicator such as methyl orange, if is acidic it turns red and in alkaline medium it turns yellow .. the solution should be neutral so it should remains orange
or use universal indicator, which turns green
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First answer is right.
Use an indicator...say phenolphthalein. It is colorless in acids. To ensure that the sulfuric acid is completely neutralized, add ammonia until the solution just turns pink.
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First answer is right.
Use an indicator...say phenolphthalein. It is colorless in acids. To ensure that the sulfuric acid is completely neutralized, add ammonia until the solution just turns pink.
Phenolphthalein is used in strong acid - strong base titration!
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Can anyone tell me what are the main topics focused in chemistry paper 6? thank u
KNow all the chemical tests for metals and non metals , as well as hydrocarbons !! , you must know the bromination experiment and the potassium permangentae one , any help ? ;D
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Chromatography
the List of solubility of salts
Titration
how to make Insoluble salts
i.e.ALL the Separating techniques
Hmm know how to use your Imagination in a Scientific*stuff from the Syllabus * way for the LAST Question in the paper ;)
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can anyone explain the past paper question of chemistry ,year 1997 november question no. 4 part f only? :-\ ???
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I dont have access to those papers. Can you take a screenshot and put it up here ?
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I dont have access to those papers. Can you take a screenshot and put it up here ?
i'll type it..
4 a. 4.2 g of cerium reacted with oxygen to form 5.16g of an oxide of cerium.complete the following to determine the formula of this oxide
1 . number of moles of cerium used
2 . mass of oxygen that reacted
3 . number of moles of oxygen atoms in oxide
4 . ratio by moles of cerium atoms to oxygen atoms
5 . formula of cerium oxide is
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I hope I'm right.
1. Ce = 140g
n = 4.2/140
=0.03 moles
2. 5.16 - 4.2 = 0.96 g
3. moles of O2
n = 0.96/ (16+16)
= 0.03 moles
4. ratio = 1:1
5. Ce + O2 ---> CeO2
Formula = CeO2
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I hope I'm right.
1. Ce = 140g
n = 4.2/140
=0.03 moles
2. 5.16 - 4.2 = 0.96 g
3. moles of O2
n = 0.96/ (16+16)
= 0.03 moles
4. ratio = 1:1
5. Ce + O2 ---> CeO2
Formula = CeO2
hmmmm,i think it should be done like this :
1 . n=m/Mr
n=4.2/75
n=0.056 moles
2 . mass of reacted Oxygen=5.96-4.2=0.96g
3 . n=m/Mr
n=0.96/(16*2)=0.03 moles
4 . 0.056:0.03=2:1
5 . CeO
do u agree?
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Hmm I think the Mr for Ce is 140g in the periodic table. :/ atomic number 58
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M/j 2005 p62 Q8
Plz help got exam tomorrow Thanks in advance:D
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can ya give me a link of the paper.
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can ya give me a link of the paper.
http://www.freeexampapers.com/past_papers.php?l=Past_Papers%2FIGCSE%2FChemistry%2FCIE%2F2005+Jun/
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M/j 2005 p62 Q8
Plz help got exam tomorrow Thanks in advance:D
I'll give you the General Idea behind it.
You put a known amount of hydrogen peroxide in a test tube that is connected to a gas syringe and burn the test tube/allow the powder inside it to decompose ... for certain time intervals ex every 1 minute record the time and the volume of gas collected
the one the gave out the most gas in the same period of time is the best catalyst.
I hope I helped :)
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I'll give you the General Idea behind it.
You put a known amount of hydrogen peroxide in a test tube that is connected to a gas syringe and burn the test tube/allow the powder inside it to decompose ... for certain time intervals ex every 1 minute record the time and the volume of gas collected
the one the gave out the most gas in the same period of time is the best catalyst.
I hope I helped :)
Oh okaaa tnxxx!!!! ;D ;D
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and By the way for the same paper,q6c, should i draw a chromatograph or explain?
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and By the way for the same paper,q6c, should i draw a chromatograph or explain?
Explain but Whenever I had chromatography exps , My teacher used to say that we have to draw and explain.
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Explain but Whenever I had chromatography exps , My teacher used to say that we have to draw and explain.
they havent given any lines for writing,they have just given a blank space so r u sure?
Yah in the other they give both line and blank space for both drawing and writing
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I'm not sure .
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I'm not sure .
ok By the way for the same question i should only show a drop of jam on the starting line and the spots which appear or i should also include 2 or 3 drops of other colours on the starting line also?
Thanks and sryt fr askign too many questions:D want to be sure:D:
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ok By the way for the same question i should only show a drop of jam on the starting line and the spots which appear or i should also include 2 or 3 drops of other colours on the starting line also?
Thanks and sryt fr askign too many questions:D want to be sure:D:
It's lemon drink ... Put a Drop at the starting line and a 2 drops since it's made of two colorings.
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It's lemon drink ... Put a Drop at the starting line and a 2 drops since it's made of two colorings.
ok got it:D
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http://www.freeexampapers.com/get_past_papers.php?l=Past_Papers%2FIGCSE%2FChemistry%2FCIE%2F2010+Jun%2F0620_s10_qp_62.pdf
Q4g
plz help as soon as possible got exam tomorrow plzzz Thanks!!!
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http://www.freeexampapers.com/get_past_papers.php?l=Past_Papers%2FIGCSE%2FChemistry%2FCIE%2F2010+Jun%2F0620_s10_qp_62.pdf
Q4g
plz help as soon as possible got exam tomorrow plzzz Thanks!!!
this is daaam easy
this is the PAPER which i gave in my IG
just think a bit and then cross check ur ans with ms
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this is daaam easy
this is the PAPER which i gave in my IG
just think a bit and then cross check ur ans with ms
Can u xplain instead of bluffing :P :P
The answer isnt in the ms idk y!
plz cn u help with this!
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ques
A) 0---- 23
10 ---- 25
20 --- 27
30 ---
i think u r smart enough to do ques a , b and c part
for d)
temp at 6cm3 for the exp1 graph
e)i)cn be answere easly if u work out ,by looking at graph or the tabel
ii)the acid would be mre concentrated or would be a stronger acidd
i think i wrote both in my exam
f)so that no traces of acid c would involve in result of experiment 2
to get fair and accurate result
g)25, wont decrease much as the exothermic acid-base reaction is completed, it would remain at 25 because any increase or decrease in temp due to exp would finally reacha t room temp (25 avg) as it looses or gains heat form the atmosphere
HOPE U UNDERTAND THE ANSWERE
any furhter doubts infrm me
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Like u continue the curve until there is no mote reaction?
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Like u continue the curve until there is no mote reaction?
yaaaa
a rough figure in estimating around 25C would work
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yaaaa
a rough figure in estimating around 25C would work
Ok Tnxxxxxxxx a lottt
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Ok Tnxxxxxxxx a lottt
but rmember that there would be no increase in temp
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Hey everyone,,
Can someone help plz to get answers to paper 1 for years before 2000?!
Thanks in advance ;)
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Hey everyone,,
Can someone help plz to get answers to paper 1 for years before 2000?!
Thanks in advance ;)
here you go dude:
http://www.freeexampapers.com/get_past_papers.php?l=Past_Papers%2FIGCSE%2FChemistry%2FCIE%2F1993-2003%2Fchemistry1993-2000answers.pdf
and the answers of the p1 will start frm page 184 onwards
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here you go dude:
http://www.freeexampapers.com/get_past_papers.php?l=Past_Papers%2FIGCSE%2FChemistry%2FCIE%2F1993-2003%2Fchemistry1993-2000answers.pdf
and the answers of the p1 will start frm page 184 onwards
I'm such an idoit :o
i have this file n used it for paper 6, but i didnt finish to the end n couldnt find paper 1 at the beginning so i taught its not available
but thanx 4 the help :)
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I'm such an idoit :o
i have this file n used it for paper 6, but i didnt finish to the end n couldnt find paper 1 at the beginning so i taught its not available
but thanx 4 the help :)
My pleasure!
Np mistake happens!
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Plz help got exam tomorrow!
http://www.xtremepapers.me/CIE/Cambridge%20IGCSE/0620%20-%20Chemistry/0620_w09_qp_32.pdf
4c (i)
Thanks
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And 5 a(ii) and 5b
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I hope I helped :)
Attached.
Excuse my drawing skills :-X
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I hope I helped :)
Attached.
Excuse my drawing skills :-X
Got it tnxxxx a lot!!!
Anyone cn do 5a(ii) and 5b?
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Got it tnxxxx a lot!!!
Anyone cn do 5a(ii) and 5b?
I drew Q.5]b) but I'm not sure of it as for a)ii) , Ask Fidato to help you out with that one :)
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Silicon Carbide is like the diamond structure. I hope this gives you the idea.
(http://4.bp.blogspot.com/_0smy438e4OI/Sf8ClMqGDTI/AAAAAAAADXE/5CClcd58YTE/s400/Silicion+Carbide.jpg)
Dia. 1 - Draw one carbon; surrounded by silicon atoms.
Dia 2 - Draw one silicon atom, surrounded by carbon atoms.
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Silicon Carbide is like the diamond structure. I hope this gives you the idea.
(http://4.bp.blogspot.com/_0smy438e4OI/Sf8ClMqGDTI/AAAAAAAADXE/5CClcd58YTE/s400/Silicion+Carbide.jpg)
Dia. 1 - Draw one carbon; surrounded by silicon atoms.
Dia 2 - Draw one silicon atom, surrounded by carbon atoms.
should the diagram look exactly the same as diamond or only i need to show the four bonds?
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should the diagram look exactly the same as diamond or only i need to show the four bonds?
Just the four bonds, yes. They are asking you to show only a 'part' of the diamond shape, that's all. ;)
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Just the four bonds, yes. They are asking you to show only a 'part' of the diamond shape, that's all. ;)
WHat i mean is that should they be in the same positions or they can be random positions?
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WHat i mean is that should they be in the same positions or they can be random positions?
Oh that! Yeah, you can draw any way you want.
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Oh that! Yeah, you can draw any way you want.
Oh ok tnxxx a lot!!
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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
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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
I am not pretty sure but I'll try
0.88/44 = gives the no.of mole of CO2= 0.02
0.02 x 12 = give no.ofmoles of carbon atoms present= 0.24
multipy 0.24 by avogaro's constant 6.023*1023=1.45*1023
I Hope I helped :)
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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
Shouldn't this be in the A-level section ?
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inQ 4 F (ii) here http://www.xtremepapers.com/CIE/Cambridge%20IGCSE/0620%20-%20Chemistry/0620_w06_qp_6.pdf
I would like to know why it is drawn below zinc ones instead of being below the magnesuim powder one
plz soooon reply
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Zinc is more reactive than iron, Magnesium is more reactive than both.
Reactivity series, here is how you learn it:
K Kitten
Na not
Ca Cat
Mg make
Al a
Zn Zoo
Fe For
Pb Poor
H2 Hungry
Cu Childeren
Ag (and these too just learn them silver comes first and then gold)
Au
So the sentence is: kitten not cat, make a zoo for poor hungry children, silver and then gold.
Learn the reactivity series, it will help you.
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Zinc is more reactive than iron, Magnesium is more reactive than both.
Reactivity series, here is how you learn it:
K Kitten
Na not
Ca Cat
Mg make
Al a
Zn Zoo
Fe For
Pb Poor
H2 Hungry
Cu Childeren
Ag (and these too just learn them silver comes first and then gold)
Au
So the sentence is: kitten not cat, make a zoo for poor hungry children, silver and then gold.
Learn the reactivity series, it will help you.
The reactivity series is given in data booklet in the form of standard reduction potentials.