Chemistry: Post your doubts here!

[Youssef Tawil]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
Number 30?? answer is C ?? Please anyone???

 

[loveyuan]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s07_qp_1.pdf

question 22 ans A . why ?!

 

[loveyuan]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
Number 30?? answer is C ?? Please anyone???

number of the mole of alcohol = 30/46
number of mole of acid = 30/60
limiting reagent is acid since its no of mole is smaller
so mass of theorical yield of ester - 30/60 x 88 = 44
perecentage = 22/44 x 100% = 50%

 

[huh]

Thanks so much. You're the best.

Focus on the H atoms across the C=C bonds.
B is trans and D is cis isomer.

 

[AhsanAfzal]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_11.pdf
someone pls explain Q24

 

[_Ahmad]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf

Q7,10,25,28,

 

[Youssef Tawil]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_qp_1.pdf

question 22 ans A . why ?!

A carbocation is the intermediate , it is electrophilic addition of alkenes and the intermediate is carbocation. C is wrong as it is free radical substitution of alkanes, B is wrong as it is nucleophilic substitution of primary halogenoalkane so it is SN2 (no formation of carbocation)

 

[SIstudy]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_11.pdf Q2, pls help :/

 

[..sacrifice4Revenge..]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s10_qp_12.pdf
q27,
ans is B, y cant it be D? :S

q35, ans C
why is Carbon not correct,
like it could be CO+1/2 O2-> CO2

 

[..sacrifice4Revenge..]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_11.pdf Q2, pls help :/

ok,
according to the data,

the equation of the reaction is.
PbCl4 +4NaBr-->Pb+2Br2+4NaCl.

now
6.980g of PbCl4
calculate its moles,Mr=349
6.980/349
=0.02mol

now since mol ration is 1:2,
we have 0.04mol of Bromine.

to get the mass.
multiply moles with its mr
= 0.04X79.9
=3.196
^ your answer.

 

[DeViL gURl B)]

Q6. need to make sure units are correct
pV= nRT
R = 8.31
T= 303K
n= 0.56/28= 0.02 mol
p= 120 000 Pa

You can solve for v (in terms of m^3)

Q7.
Formation of propanone

3C (s) + 3H2 (g) + 1/2 O2 (g)--> C3H6O (g)

heat of reaction = heat of combustion of reactants- heat of combustion of products
= 3(-394)+3(-286)-(-1786)
=-254

Q13. ? What answer?

Q14.
I'm guess the hurdle is getting the balanced equation?

10Al + 3Ba(NO3)2 --> 5Al2O3 + 3BaO + 3N2

moles of barium nitrate = 0.783 / 261 = 0.003
moles of N2 = 0.003
vol of N2 at RTP = 0.003 x 24000 = 72 cm^3

Q38.
Mr of alcohol = 74
Moles of alcohol used = 70/74 = 0.946
Moles of alcohol converted into products = 0.946 x 62% = 0.586

1. If 0.586 mol of butanone was obtained, it would weight 0.586 x Mr of butanone = 0.586 x 72 = 42.2 g (statement 1 true)
2. If 0.586 mol of butanoic acid was obtained, it would weight 0.586 x Mr of butanoic acid = 0.586 x 88 = 51.6 g (statement 2 true)
3. If 0.586 mol of 2-methylpropanoic acid was obtained, it would weight 0.586 x 2-methylpropanoic acid = 0.586 x 88 = 51.6 g (statement 3 true)

Well thank you soo much for the help!
But I didn't get question 6 I did all the possible ways..
Would U please explain it ..

For question 13 the answer is c

 

[..sacrifice4Revenge..]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_11.pdf
someone pls explain Q24

ans is B, butan-2-ol

so,
now if you oxidise
A, butan-1-ol, you get an aldehyde on mild oxidation and carboxylic acid on further, 2 products, so wrong answer.
B, oxidising butan-2-ol gives us only butanone. so it's the correct option.

draw out all the given structures, or do it mentally for questions like this.

 

[GCE As and a level]

..sacrifice4Revenge.. Metanoia ZaqZainab AND @ EVERY BODY
Could u plz help me with this
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s07_qp_1.pdf

Q12...Answer B>>I cant understand the question :s
Q17...Answer C>>Why SO2 is produced instead of SO3......Its written excess oxygen....and in other questions in a different year,they write that SO3 is produced :s
Q18...Answer D>>Again i cant understand the questions
Q21...Answer D
Q22..Answer A>>Could u plz give me a brief explanation for the mechanisms we have in AS syllabus ??!!
Q25..Answer C
Q26..\answer C
Q34..Answer D>>How am i supposed to know
Q38..Answer A>>Shouldn't the answer be C :s
THNX GUYS

 

[DeViL gURl B)]

Oct/Nov 2012 variant 11
Guys please explain question 17 the answer is D
Q 11 answers 11 answer is A

Q 10 answer is C
Question 15 answer is B
Question 4 answer is A ?? How??
Please full explanation needed!!

 

[chishtyguy]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_12.pdf
q27,
ans is B, y cant it be D? :S

q35, ans C
why is Carbon not correct,
like it could be CO+1/2 O2-> CO2

Question 35
Remember it particularly mentions atmosphere,
Reaction of Nitrogen and sulphur can occur in atmosphere while CO has triple bond it can't take place

Q 27
Butan-2-ol forms 2 alkene and a cistrans
while in option D, No cistrans only 2 alkene

 

[_Ahmad]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf

Q7,10,25,28,

 

[chishtyguy]

WHO HATES CHEMISTRY??

Don't say that.. A's Chemistry requires a lot of practice and cleared concept... It's MCQs are hell... But ones's u get ur concept get cleared.. iA u can conquer it.. Just dont lose hope...

 

[kingo44]

if u hydrolyse ester how many oh are produced

 

[kingo44]

how 2 are formed is the hydroxyl group in carboxylic acid applicable also please clarify

 

[GCE As and a level]

Don't say that.. A's Chemistry requires a lot of practice and cleared concept... It's MCQs are hell... But ones's u get ur concept get cleared.. iA u can conquer it.. Just dont lose hope...

Man i have practiced most of P1 chemistry and still i am scoring in 20's :s
In p 21 , I think thatr i willlose 20 marks due to my silly mistakes in the silly questions
In p 32, i can lose up to 7-8 marks
so in P11,I need a high score to get an overall A incase{and for sure} the gt is high
Any way thanks man..and sure I will never lose hope...Inshallah Allah will help me
Allah kareem