Chemistry: Post your doubts here!

[CaptainDanger]

9701_s11_qp_12.pdf

9701_s11_ms_12.pdf

Q 29???

 

[Amy Bloom]

isnt SF4 trigonal bi-pyramidal ? SF6 is octahedral or square bipyramidal or for that any 5 bonding pair and 1 lone pair, 4 bonding pair and 2 lone pair will be square bipyramidal.

No. SF4's got 4 S-F bonds. So, it's gonna be "square" at the "base". Plus you've got 2 lone pairs at the top. If you consider the valence shell electron pair theory (lonepair/lonepair > lonepair/bond pair> bond pair/bond pair), the 2 lone pairs on top will repel other bonded pairs and hence the shape's going to be like a pyramid, but square based. Got it?

 

[Student12]

No. SF4's got 4 S-F bonds. So, it's gonna be "square" at the "base". Plus you've got 2 lone pairs at the top. If you consider the valence shell electron pair theory (lonepair/lonepair > lonepair/bond pair> bond pair/bond pair), the 2 lone pairs on top will repel other bonded pairs and hence the shape's going to be like a pyramid, but square based. Got it?

Yeaa point ! thanks

 

[Amy Bloom]

Yeaa point ! thanks

u welcome

 

[Zishi]

9701_s11_qp_12.pdf

9701_s11_ms_12.pdf

Q 29???

The answer should be D. The -OH on left won't be oxidised by cold, dilute KMnO4, but the alkene would be oxidised to a diol. When hot, conc. KMnO4 is used, that -OH group is oxidised to a ketone and the carbons with the double bond in the ring(alkene group) would be oxidised to Carboxylic acid and a ketone respectively.

 

[geek101]

Can someone explain Q14 and 16?

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s03_qp_1.pdf

thank you

 

[Zishi]

Can someone explain Q14?

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s03_qp_1.pdf

thank you

C, because a lone pair from the chloride ion would attack the AlCl3 molecule. As Aluminium has an incomplete octet, there should be an empty orbital to accept the lone pair from chloride ion.

 

[Student12]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w03_qp_1.pdf

Can anyone explain Q2,3,15 and 20 ??

 

[smartangel]

can someone please explain Q1..c i. we get 0.04 moles of acid and alcohol,,dont we subtract it from 0.1 to get moles at equilibrium?
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_s11_qp_22.pdf

 

[smzimran]

can someone please explain Q1..c i. we get 0.04 moles of acid and alcohol,,dont we subtract it from 0.1 to get moles at equilibrium?
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_22.pdf

No. of moles of NaOH is 0.04 as we calculated earlier meaning (0.1 - x) = 0.04
Because alcohol was the reactant and equilibrium concentration of reactant is given by:
(initial concentration - x) so (0.1 - x) = 0.04 and
therefore x = 0.06
So concentretion of acid and alcohol is (0.1 - x) = (0.1 - 0.06) = 0.04

This paper reminds me of last year, I gave this very paper in the exam last year in AS

 

[smartangel]

No. of moles of NaOH is 0.04 as we calculated earlier meaning x = 0.04
So concentretion of acid and alcohol is found out by
= (0.1 - x)
= (0.1 - 0.04)
= 0.06

This paper reminds me of last year, I gave this very paper in the exam last year in AS

haha so does your answer match with the marking scheme?
coming back to the question.. i really dont get it. could you please explain why have they taken 0.04 for the acid and alcohol.their equilibrium moles should be 0.06.?

 

[smzimran]

haha so does your answer match with the marking scheme?
coming back to the question.. i really dont get it. could you please explain why have they taken 0.04 for the acid and alcohol.their equilibrium moles should be 0.06.?

I made a mistake earlier i corrected it check the first post...
Btw, i dont remember my solution from last year but i do remember that i got Kc = 2.25 so i must have done it right there

 

[smartangel]

I made a mistake earlier i corrected it check the first post...
Btw, i dont remember my solution from last year but i do remember that i got Kc = 2.25 so i must have done it right there

oh okay. thanks a lot!

 

[smartangel]

Q4 b. how is it secondary alcohol as mentioned in the marking scheme? OH is on the 4th carbon atom.. is it because the c atom with OH is joined to 2 other c-atoms?
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_s11_qp_23.pdf

 

[Zishi]

Q4 b. how is it secondary alcohol as mentioned in the marking scheme? OH is on the 4th carbon atom.. is it because the c atom with OH is joined to 2 other c-atoms?
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_23.pdf

Yes.

 

[smartangel]

Yes.

okay thanks.. if we just write alcohol will it be marked as a wrong asnwer?

 

[Zishi]

okay thanks.. if we just write alcohol will it be marked as a wrong asnwer?

Probably. I have seen some mark schemes which do cut a mark for not writing the type of alcohol.

 

[Student12]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
Can anyone explain 1,4,22,30 and 39 from this paper plz ??

 

[KurayamiKimmi]

Hey i have a doubt related to "Hess's Law calculations"
I always get confused what equation's enthalpy change to minus and what to plus - so can anyone please explain Hess's Law calculations ? ^^

 

[workaholic]

i dont get why we use excess air when converting SO2 to SO3 in the contact process......i know it shifts the equilibirium shifts to the right but i dont get why...??????