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Chemistry: Post your doubts here!

Metanoia

Metanoia

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Hijab said:
Can u explain this question to me as well?
Click to expand...
Is the answer C?

The description means we have a mixture of carbonate
1) one which decomposes under heat to give CO2 (CaCO3)
2) one which does not decompose under heat, but later reacts with acid to give CO2 (BaCO3)
 
Hijab

Hijab

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Thank you... Yes its C
Metanoia said:
Is the answer C?

The description means we have a mixture of carbonate
1) one which decomposes under heat to give CO2 (CaCO3)
2) one which does not decompose under heat, but later reacts with acid to give CO2 (BaCO3)
Click to expand...
 
A

_Ahmad

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umair1161 said:
Hello guys!

Can you please help me with:

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_12.pdf

question 17!

Thanks in advance! :)
Click to expand...

Calculate the number of moles of oxygen using Pv=nRT
n=0.0121

they have given us the mass of the elements (1.15g) so we need to check which element will react with 0.0121 mol of oxygen

2Ca + O2 ----> 2CaO
n(Ca)=1.15/40.1=0.0287
using mole ratio 2 moles of Ca react with 1 mole of O2 therefore 0.0287 mole of calcium will react with 0.0143 mol of oxygen (so this is incorrect)

4Na + O2 ----> 2Na2O
n(Na)=1.15/23=0.05
using mol ratio 4 mole of sodium react with 1 mol of oxygen therfore 0.05 mol of sodium will react with 0.0125 mol of oxygen (so this is correct)

answer = D

Hope this makes sense.
 
MaboroshI_I

MaboroshI_I

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loveyuan said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_11.pdf

question 29
idono why i cant solve isomer question everytime !!!! TT
Click to expand...

An easy, albeit time consuming way to figure these questions out is to simply draw the isomers. You know there's a double bond, so it must show geometric isomerism - cis and trans, that makes 2. But they aren't asking for just geometric isomers, they're asking for all the isomers. Another one would be but-1-ene. So that makes 3. I know this isn't the best way to work it out, but it's better than nothing. :)
 
K

kitkat <3 :P

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MaboroshI_I said:
An easy, albeit time consuming way to figure these questions out is to simply draw the isomers. You know there's a double bond, so it must show geometric isomerism - cis and trans, that makes 2. But they aren't asking for just geometric isomers, they're asking for all the isomers. Another one would be but-1-ene. So that makes 3. I know this isn't the best way to work it out, but it's better than nothing. :)
Click to expand...

but there is a differenc betweeen structural and stereo isomers isnt it :/?
 
MaboroshI_I

MaboroshI_I

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kitkat <3 :p said:
but there is a differenc betweeen structural and stereo isomers isnt it :/?
Click to expand...
The question says 'structural or otherwise' :S I don't know, I could be wrong.

Could you or someone else help me with the questions I posted earlier? Just on the previous page.
 
A

Ahmed Aqdam

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ZaqZainab said:
I thought more the lone pairs more the replution and hence more the angle
Q20 i am confused about A and B??
Click to expand...
More repulsion when more lone pairs so the bonding pairs are pushed closer together and hence less angle.

20: The cis isomer is the one in which the two H are on the same side of the C-C double bond.
The one in B is trans as H is on different side.
 
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