Chemistry: Post your doubts here!

[Metanoia]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_1.pdf
Q4 D is the answer
Q8 D is the answer what about A? PV=nRT n and R and T constant so P=1/V so P increases V decreases? and i do understand why D is correct but why is A wrong?
Q22 i have a problem with angles any notes will do?
Q26 C or B isnt it the same thing C is the actual answer
Q29 what about C? D is the answer
Q38 why int 2 correct
Q39 it is a primary alcohol so shouldn't it be forming an aldehyde

s08qp1

Q4. BaO2 anion is two oxygen atoms with a total of -2 charge, hard to type out......(O2)2-
We have one single bond among the two atoms and 1 extra electron to each atom.

Q8. If you link it to y = 1/x , you should remember its a curve, with the axis as asymptotes.

Q22. The carbons are all saturated with 4 single bonds, so tetrahedral, 109.5

Q26.
Increase in the 2 oxygen means that the 2 OH has been oxidized to 2 COOH groups.
The two OH must be primary alcohols. Since is an unbranched butanol, the OH groups are on carbon 1 and 4.
If you choose B, the OH attached to the 3rd carbon becomes a ketone instead of the required acid.

Q29. C is ester group, not acid group.

Q38. hmm.. maybe you can explain why you think 2 is correct?

Q39. Its a secondary alcohol.

 

[Ahmed Aqdam]

Thanks
i am still confused about
Q9 how did you find the moles? shouldn't metallic salt be 0.10/(50*10^-3)=2??
SO3 2- be 0.10/(25*10^-3)=4??


Thanks
Q19 why not
CH3-CH2-CHI2??

The second carbon has two H which are same and last one has two I which are same so not optical isomer.

 

[sadiaali]

Please anyone Q 4.Thanks a lot for giving your time explaining me.
Link:http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w13_qp_13.pdf
MS: http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w13_ms_13.pdf

 

[Ahmed Aqdam]

Please anyone Q 4.Thanks a lot for giving your time explaining me.
Link:http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_qp_13.pdf
MS: http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_ms_13.pdf

X will be in Group 7 as it forms X- ions and can be oxidised. Option D has ionisation energies of group 7 element (iodine) so it will be D.

 

[Suchal Riaz]

If anyone has any problem ask me tag me 'suchal riaz' or text me if i am not available.

 

[_Ahmad]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w13_qp_13.pdf

can anyone please explain Q27

 

[Suchal Riaz]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_qp_13.pdf

can anyone please explain Q27

it has a chiral carbon. so think of a single center carbon with one H attached on OH attached and two other groups attached. to make it chiral these two must be difficult. to make n smallest one must be CH3 and other must be C2H5

 

[MiniSacBall]

it has a chiral carbon. so think of a single center carbon with one H attached on OH attached and two other groups attached. to make it chiral these two must be difficult. to make n smallest one must be CH3 and other must be C2H5

Well sir you have got this one wrong, the question says that it doesn't react with hot,acidified KMnO4. Thus, it has to be a tertiary alcohol.
So to make n smallest i has to CH3, C2H5 and C3H7.
So it would be C

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_qp_13.pdf

can anyone please explain Q27

I have answered above which is C

 

[_Ahmad]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_qp_13.pdf

Q3,31,

 

[ZaqZainab]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
Q8
B and D the same thing?

 

[Ahmed Aqdam]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
Q8
B and D the same thing?

Combustion of PbO is when it reacts with O2. This is not the combustion of Pb but PbO.
Formation of PbO is when Pb and O2 react to form PbO.

 

[Suchal Riaz]

Well sir you have got this one wrong, the question says that it doesn't react with hot,acidified KMnO4. Thus, it has to be a tertiary alcohol.
So to make n smallest i has to CH3, C2H5 and C3H7.
So it would be C



I have answered above which is C

i didn't read that part. sorry. i was watching pokemon trying to resurrect my sad old memories :'(

 

[Hadi Murtaza]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_qp_13.pdf

Q3

moles of TlNO₃ = (10 × 0.3)/1000 = 0.003 moles
moles of NH₄VO₃ = (20 × 0.1)/1000 = 0.002 moles

So it takes 0.002 moles of V to oxidize Tl(+1) to Tl(+3)
or it takes 0.003 moles of Tl to reduce V(+5) to V(unknown)
Now cross multiply
V(5 - unkown) * 0.002 = 0.003 * Tl(3 - 1)
V(5 - unkown) = (2 * 0.003)/0.002
V(5 - unkown) = 3

So change in oxidation state is - 3
Anwer: B

 

[..sacrifice4Revenge..]

What factor decides that in finding enthalpy change of a reaction do we need the formation data or combustion data?!

 

[Suchal Riaz]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_qp_13.pdf

Q3,31,

 

[ZaqZainab]

Combustion of PbO is when it reacts with O2. This is not the combustion of Pb but PbO.
Formation of PbO is when Pb and O2 react to form PbO.

opps i mean A and D are the same thing right then?

 

[Suchal Riaz]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_qp_13.pdf

Q3,31,

H3 + means three hydrogen bonded to each other with a positive charge. so it has three protons. no neutrons. and 2 electrons are there is a positive charge on it.
L + is one lithium ion with one lithium-6 which has lost one electron. lithium has 3 protons. 6-3=3 neutrons. and has lost one electron so total 2 electrons.
now we have data. both contains three protons. both contain 2 electrons. but they do not contain same number of neutrons. (1) and (2) is correct. (3) is wrong. answer B

 

[Suchal Riaz]

opps i mean A and D are the same thing right then?

enthalpy change of combustion of lead means complete oxidation. until it oxidises to Pb3O4. that is same as formation of Pb3O4 not of PbO

 

[Suchal Riaz]

What factor decides that in finding enthalpy change of a reaction do we need the formation data or combustion data?!

enthalpy change of combustion means COMPLETE combustion. Carbon can form two products when burning: CO2 or CO.
enthalpy change of combustion of C is same as enthalpy change of formation of CO2 but not same as enthalpy change of formation of CO

 

[Suchal Riaz]

ahmed faraz