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Author Topic: CHEM AND BIO HELP AND TIPS HERE  (Read 356817 times)

nid404

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2295 on: May 29, 2010, 03:36:34 pm »
Quote from: sarasa on May 26, 2010, 07:10:53 pm
Here is one example ...
It came as a graph in paper3 may/june 2009 Q5

this was answered somewhere before. I'll look for the explanation
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Offline basharooo

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2296 on: May 30, 2010, 07:53:46 am »
guys what is the big idea about MOLES , Like i study the chapter from my textbook , but when i open the
past papers i cant really solve anything .. ?
the moles are partially hard
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nid404

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2297 on: May 30, 2010, 08:00:43 am »
nope they're the easiest part of chemistry ;)
Just post your question here...I'll answer 'em  :) I have AS chem tom  :P
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Offline CatAly$t

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2298 on: May 30, 2010, 08:57:27 am »
pls,

can somebody answer for me q5 in 2002 june....

http://www.freeexampapers.us/IGCSE/Chemistry/CIE/2002%20Jun/0620_s02_qp_3.pdf

no answer on ms...i just wanna  check my answers...

thx
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nid404

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2299 on: May 30, 2010, 09:17:51 am »
the a) part?

Liquids take the shape of the container, they maintain their volume. The intermolecular forces in liquids are significant and therefore, they do not expand to occupy all the space available (as gases do). A given mass of liquid has a fixed volume. also molecules in liquid have less k.e as compared to that of gases.Particles in gases have very weak intermolecular forces and high kinetic energy, hence the particles move independent of each other and occupy the space available to them.

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Offline CatAly$t

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2300 on: May 30, 2010, 10:33:38 am »
Quote from: nid404 on May 30, 2010, 09:17:51 am
the a) part?

Liquids take the shape of the container, they maintain their volume. The intermolecular forces in liquids are significant and therefore, they do not expand to occupy all the space available (as gases do). A given mass of liquid has a fixed volume. also molecules in liquid have less k.e as compared to that of gases.Particles in gases have very weak intermolecular forces and high kinetic energy, hence the particles move independent of each other and occupy the space available to them.



thanks  8)...pls try to solve for me the questions on the last page pls....if u have time  ;)

thx

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Offline Meticulous

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2301 on: May 30, 2010, 10:39:18 am »
b)i) rate= time and volume. In other words, its the volume produced and the time taken.

ii) CO2 due to lower molecular mass. or less density

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Offline CatAly$t

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2302 on: May 30, 2010, 10:43:58 am »
Quote from: ~ A.F ~ on May 30, 2010, 10:39:18 am
b)i) rate= time and volume. In other words, its the volume produced and the time taken.

ii) CO2 due to lower molecular mass. or less density



thx... :D

and the last page please....i really su*k in mole calculations  :'(...if possible,with some explanations pls.... :)

thx
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Offline Ivo

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2303 on: May 30, 2010, 01:00:49 pm »
Quote from: CatAly$t on May 30, 2010, 10:43:58 am
thx... :D

and the last page please....i really su*k in mole calculations  :'(...if possible,with some explanations pls.... :)

thx

The equation you need to use is:

                      Volume of gas (in dm3)
Moles of gas = --------------------------
                                      24

Note to convert cm3 to dm3, divide quantity by 1000 (e.g. 20cm3/1000=0.02dm3)

This is the proper theory and equation behind my calculations below.

Here are the answers for 5) c) as requested:

i)   Moles of C4H6: 0.02/24=0.000833
     From equation, we know 2 moles of C4H6 reacts with 11 moles of O2
     Therefore, moles of O2: 0.000833*5.5=0.00458
     Therefore, volume of O2: 4.58*24*1000=110cm3

ii)  From equation, we know 2 moles of C4H6 produces 8 moles of CO2
     Therefore, moles of CO2: 0.000833*4=0.00333
     Therefore, volume of CO2: 0.00333*24*1000=80cm3

iii) From equation, we know 2 moles of C4H6 produces 6 moles of H2O
     Therefore, moles of H2O: 0.000833*3=0.0025
     Therefore, volume of H2O: 0.0025*24*1000=60
     Therefore, total volume of gases is simply volume of CO2 + volume of H2O:
     80+60=140cm3

     Alternatively, 8+6=14, so 2 moles of C4H6 produces 14 moles of products
     Therefore, moles of products: 0.000833*7=0.00583
     Therefore, volume of products: 0.00583*24*1000=140cm3

For part d), you use this formula:

             Mass
Moles = ------
               Mr

d)  From the above equation, 1 mole of butyne forms 3 moles of water
     Number of moles of butyne reacted: 9/54=0.167
     Number of moles of water formed: 0.167*3=0.5
     Mass of water formed: 0.5*(2+16)=9g

I hope this has helped. :D
« Last Edit: May 31, 2010, 11:03:33 am by Ivo »
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holtadit

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2304 on: May 30, 2010, 01:10:27 pm »
@Ivo  +rep :)  Keep it up !
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Offline CatAly$t

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2305 on: May 30, 2010, 02:59:55 pm »
Quote from: Ivo on May 30, 2010, 01:00:49 pm
The equation you need to use is:

                      Volume of gas (in dm3)
Moles of gas = --------------------------
                                      24

Note to convert cm3 to dm3, divide quantity by 1000 (e.g. 20cm3/1000=0.02dm3)

This is the proper theory and equation behind my calculations below.

Here are the answers for 5) c) as requested:

i)   Moles of C4H6: 0.02/24=0.000833
     From equation, we know 2 moles of C4H6 reacts with 11 moles of O2
     Therefore, moles of O2: 0.000833*5.5=0.00458
     Therefore, volume of O2: 4.58*24*1000=110cm3

ii)  From equation, we know 2 moles of C4H6 produces 8 moles of CO2
     Therefore, moles of CO2: 0.000833*4=0.00333
     Therefore, volume of CO2: 0.00333*24*1000=80cm3

iii) From equation, we know 2 moles of C4H6 produces 6 moles of H2O
     Therefore, moles of H2O: 0.000833*3=0.0025
     Therefore, volume of H2O: 0.0025*24*1000=60
     Therefore, total volume of gases is simply volume of CO2 + volume of H2O:
     80+60=140cm3

     Alternatively, 8+6=14, so 2 moles of C4H6 produces 14 moles of products
     Therefore, moles of products: 0.000833*7=0.00583
     Therefore, volume of products: 0.00583*24*1000=140cm3

For part d), you use this formula:

             Mass
Moles = ------
               Mr

d)  From the above equation, 1 mole of butyne forms 3 moles of water
     Number of moles of butyne reacted: 9/54=0.167
     Number of moles of water formed: 0.167*3=0.5
     Mass of water formed: 0.5*(2+16)=9g

I hope this has helped. :D

thanks man  ;D....bath rocks!!! ;)
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Offline Helium

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2306 on: May 30, 2010, 04:25:38 pm »
Whats heated and instead of melting turns into solid? ???
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nid404

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2307 on: May 30, 2010, 04:30:26 pm »
huh...when you heat anything, molecules in it will always move away from each other.
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Offline Ivo

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2308 on: May 30, 2010, 04:30:58 pm »
Quote from: Helium on May 30, 2010, 04:25:38 pm
Whats heated and instead of melting turns into solid? ???

I don't get what you mean by "whats heated", and for your second question, freezing/solidification is the process of turning a liquid into a solid.
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Offline Helium

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2309 on: May 30, 2010, 05:27:19 pm »
naah, it's just one of my friends planning to take chem next year,

so he challenged me to anwser that question, he said it's eggs, LOL :D

Yes i know it sounds lame , i told him a chemical reaction took place when boiling or cooking the egg,

but he still loves that question ;D
« Last Edit: May 30, 2010, 07:10:10 pm by Helium »
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