Chemistry: Post your doubts here!

[LeoMessi]

More help please!
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23 C because only Pentan-3-ol has a chiral carbon. Drawing the displayed formula for such type of questions REALLY helps
30 Na will react with an alcohol to give R-O Na , the number of oxygens remains the same. Elimination will occur with Al2O3, with option B esterification will occur with the acid which increases the number of oxygen atoms and in option C OH group will be replaced by HBr. So D is the answer

 

[h4rriet]

Yet again im posting please do help
" Question number 7 please help
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf
And question number 11 and 23
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf "

What you have to do is draw ICE charts for all the equations (A, B, C and D). Then see if the sum of equilibrium moles is 2+x/2.
Here's the ICE chart for D:

 

[HubbaBubba]

23 C because only Pentan-3-ol has a chiral carbon. Drawing the displayed formula for such type of questions REALLY helps
30 Na will react with an alcohol to give R-O Na , the number of oxygens remains the same. Elimination will occur with Al2O3, with option B esterification will occur with the acid which increases the number of oxygen atoms and in option C OH group will be replaced by HBr. So D is the answer

I wrote Na for 30, but the answer is CH3COOH. I have no idea why, as that would give an ester, and that has two O atoms.

 

[h4rriet]

Yet again im posting please do help
" Question number 7 please help
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf
And question number 11 and 23
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf "

23. Ethene is half of the products. So there must be 2 ethene molecules and 1 propene and methane. 3+1+(2x2)=8. The compound that is cracked must contain 8 carbons.

 

[h4rriet]

I wrote Na for 30, but the answer is CH3COOH. I have no idea why, as that would give an ester, and that has two O atoms.

Check the mark scheme again. Pretty sure it's Na.

 

[Dr.MMM]

which year?

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_11.pdf

 

[HubbaBubba]

Check the mark scheme again. Pretty sure it's Na.

Sorry misread the ms

 

[h4rriet]

More help please!
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24. Because of the rings, the compound can't be planar. Because of the rings, there can exist no cis-trains isomers.
8. Pressure depends on the mole ratio, so you'll need to be calculating the moles here. Mass of H2=2 g, molecular mass=2, so n=1. Calculate the total moles in A, B, C and D. C's the answer, if I'm not mistaken.
11. Draw an ICE (initial moles, change in moles, equilibrium moles) chart.

 

[Raiyan3]

What you have to do is draw ICE charts for all the equations (A, B, C and D). Then see if the sum of equilibrium moles is 2+x/2.
Here's the ICE chart for D:

Rightttt Thanks alot buddy! That really did help buddyy!

 

[HubbaBubba]

24. Because of the rings, the compound can't be planar. Because of the rings, there can exist no cis-trains isomers.
8. Pressure depends on the mole ratio, so you'll need to be calculating the moles here. Mass of H2=2 g, molecular mass=2, so n=1. Calculate the total moles in A, B, C and D. C's the answer, if I'm not mistaken.
11. Draw an ICE (initial moles, change in moles, equilibrium moles) chart.

I did draw an ICE, but I don't understand how they got 4(b-x) at the bottom. I just got (b-x)^2

 

[imperial]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_11.pdf

20

 

[Raiyan3]

Question number 11 please
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf

 

[Alice123]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_11.pdf
Q4 please Ahmad Zaeem

 

[darkxangel]

How to do this ?

 

[darkxangel]

I think C. (Na can react with both -CO2H and OH, there is 3 in C so -3 but NaOH only with -CO2H so -1) I'm not sure though as I didn't revise from a long time.

I have a question : http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_11.pdf

Number 9, the answer is D but I don't know how to get it.

i didn't quite get it :/
I get the part where Na reacts with both -CO2H and -OH but after that i don't get it ..
and
yes it is C.

 

[h4rriet]

I did draw an ICE, but I don't understand how they got 4(b-x) at the bottom. I just got (b-x)^2

If x moles of HI dissociates, then H2 and I2 gain x/2 moles (mole ratio 2:1). Amount of HI left = b-x. Now, Kp=p(I2)xp(H2)/p(HI)^2. [(x/2)*(x/2)]/(b-x)^2 will simplify to D.

 

[imperial]

i didn't quite get it :/
I get the part where Na reacts with both -CO2H and -OH but after that i don't get it ..
and
yes it is C.

Na reacts with both groups to form ONa- which is charged (-1), there is three so 3 ONa- will form

NaOH is the same thing but with only -CO2H group.

 

[ShaanSiddiq090909]

Someone please post the link for solved yearly past papers for chem

 

[h4rriet]

How to do this ?View attachment 28899

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_11.pdf

20

With cold, dilute KMnO4, the C=C bond turns into C(OH)-C(OH). With hot, concentrated, it turns into C=O and O=C.

 

[darkxangel]

Na reacts with both groups to form ONa- which is charged (-1), there is three so 3 ONa- will form

NaOH is the same thing but with only -CO2H group.

Oh Alright . Thanks