Chemistry: Post your doubts here!

[kingo44]

Which statements are true for an SN2 reaction?
1 One bond is broken as another bond is formed.
2 The formation of a transition state involves the collision of two molecules or ions.
3 A carbon atom in the transition state is bonded, either fully or partially, to five other atoms

 

[Youssef Tawil]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
Number 11 ?? anyone please??? Answer is C

 

[GCE As and a level]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
Number 11 ?? anyone please??? Answer is C

my doubt too
if u got the answer plz tag me

 

[Najam0096]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w06_qp_1.pdf

Can someone help me with q4?

 

[kruti]

srry man
i have the same doubts :s
how much u scored in this paper ??

I didn't count. but must be in the 20s somewhere.

 

[kruti]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w06_qp_1.pdf

Can someone help me with q4?

I am not too sure about this but I think D is the right answer because as you down the alkane homologous series, the boiling point and melting point increases. So, maybe more energy would be needed for larger alkanes to undergo combustion and therefore more residual gas is produced by smaller alkanes over a certain period of time.

 

[FarahMJ]

Please help with these...i will really appreciate it!

Ans B

1 and 2 correct

 

[Hadi Murtaza]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
Number 11 ?? anyone please??? Answer is C

my doubt too
if u got the answer plz tag me

U dont even have 2 do any calculations of da stoichiometry. Valency of C is 4, valency of Al is 3, so u cross multiply n forms Al₄C₃. All other options wud fail 2 satisfy da octet rule

 

[kruti]

Please help with these...i will really appreciate it!

Ans B

1 and 2 correct

Question 26 is quite easy. Both W and Y would have to get changed to a halogenoalkane before the final products are formed.
I

 

[Metanoia]

U dont even have 2 do any calculations of da stoichiometry. Valency of C is 4, valency of Al is 3, so u cross multiply n forms Al₄C₃. All other options wud fail 2 satisfy da octet rule

S11Q12

In this case, the cross multiplication does give us the answer, but have to be careful at A levels, not all species need to satisfy the octet rule.
E.g AlCl3 and SO4 2-


This was what i suggest some posts ago

Understand that whatever moles of C we have at the beginning will eventually be the same number of moles of C in CO2 at the end.

Let x and y be the ratio of Al and C respectively.
AlxCy --->???---> CO2

Working backwards from CO2,
moles of CO2 = 72/24 000 = 0.003 moles = moles of C in AlxCy

Going through the options
A Al 2C3, moles of Al2C3 = 0.144/90 = 0.0016, moles of C = 0.0016 x 3 = 0.0048 (incorrect)
B Al 3C4 , moles of Al3C4 = 0.144/129 = 0.0016, moles of C = 0.0016 x 4 = 0.0045 (incorrect)
C Al 4C3 , moles of Al4C3 = 0.144/144 = 0.001, moles of C = 0.001 x 3 = 0.003 (BINGO!)
D Al 5C3

 

[Youssef Tawil]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf
Number 28????? answer is C

 

[Youssef Tawil]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_13.pdf
Number 12 ?? answer is D

 

[kingo44]

please metanoia more buddy more u made my day good i want mire

 

[kingo44]

i wait for u [atiently alot

 

[Metanoia]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w06_qp_1.pdf

Can someone help me with q4?

W06qp1

Just take 10cm3 of CH4 as example and form a balance eqn

CH4 + 2O2 --> CO2 + 2H2O

We will use up 20 cm3 of O2 and produce 10 cm3 of CO2.

So 50 cm3 of unused O2 and 10 cm3 of CO2 gives us total of 60cm3 of gas for CH4.

So its graph D if we look at CH4.

 

[kingo44]

metanoia can u do may june 2002

 

[Metanoia]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_13.pdf
Number 12 ?? answer is D

w11q13

Check post #9228 on pg 462

It is likely that you wrongly included Ag (s) into the Kc expression? If so, remember we don't include solids in the Kc.

 

[ashcull14]

 

[ashcull14]

 

[ashcull14]