2016 A Level H2 Chemistry Paper 2, 3, 1 discussions

last SG · 2016-11-08T20:10:45+00:00

I would think they should accept only NO2+S02=SO3+NO then regeneration bla bla blaso its like a homogeneous catalyst and Oxidising agent i would think elect...

ArJoe SG

Anyway in the majority of the years, the A grade should be at 70%, unless the paper is easy or difficult, otherwise there is usually no need to moderate i think….

Thefire521 SG

are you from top 5 jc? You seem to be very good at chem

haha no i setted the paper was just interested in the discussions of students sitting for my little test hahaha

@houdini yeah i think so long as the examiner sees you write h bond stronger that should be more or less it. 3 lines they dont expect you to explain so much so even if you gave that extra d.f thinigs, it should be fine so long you say one has h bond one dont have

houdini_00 SG

Thus, let's not give ourselves death sentences over one paper alone. I estimated a loss of 20/60 today for Paper 2 but I'm still optimistic that as long as you strive for Paper 3 and score decently to make up for your grades, you can still make it. A or B, that's Cambridge's job to assign our grades for us isn't it. Jiayou!

Thomas00 SG

are you from top 5 jc? You seem to be very good at chem

Fire521's concept sounds very solid.

ArJoe SG

haha no i setted the paper was just interested in the discussions of students sitting for my little test hahaha

for the cu dissolve in acid qn, i quote the eqn cu arrow cu2+ +2e- but irreversible arrow. Isit ok? Then the 2h+ +2e- arrow h2 also irreversible arrow. Isit ok? and for the no2 and so2 qn, i just wrote the eqn no2+so2arrow no+so3. Isit possible to get 1 mark lol.. i sound so pathetic

ArJoe SG

Fire521's concept sounds very solid.

Yup that was why i thought she/he was rjc/hci or h3 chem student..

Sir3 SG

For the lower melting point in question 1 part 1, why cant i say that the molecules contains more cis double bond thus less effective packing and thus lower degree of molecular symettry which leads to lower melting point? It you look at the table on fatty acids, the number of cis for each molecule went up thus shouldnt there havingg more cis in the triester outweigh that of the hydrogen bond formed?

ArJoe SG

You meant 20/72?

Thomas00 SG

Anybody found or have the suggested answers for P2 yet? Just curious and want to see :)

How many marks did you all lose approximately? All the best for remaining papers!

Thefire521 SG

Since the question asked you to quote data from data booklet, you should have just copied wholesale and wrote down the e value since they only wanted you to test feasibility of the reaction, but not write down the reaction occuring (there is no reaction anyway) If this was an electrochem cell and they asked you write down the half equations of the reactions occuring at anode and cathode, then yes you use irreversible arrows.

though i think they wouldn't penalise you if they are lenient on this

no2+so2arrow no+so3 should be worth 1 mark and the regeneration another mark. writing that it is a homogeneous catalyst probably gives you the last mark and explaining

@thomas there wouldnt be suggested answers for paper 2 since nobody will guarantee (even ultimate tutor ultima) since its collected up

houdini_00 SG

You meant 20/72?

Planning's a separate component. I estimate 8/12 for planning because of calculation errors at the end and 38/60 for the other segment. Not a decent score. I need to use P3 and P1 to pull me up, therefore.

Thefire521 SG

This is bio-

A tri-ester is simply the compound formed after an esterification reaction between glycerol and fatty acids.

Then the question asked you: Why triester melting point lower than the fatty acid monomer?

First assumption you made is that the double bonds are cis. Do you know that they can be trans double bond and trans double bond can give MORE effective packing and therefore higher melting point? - so this is already a huge assumption you made

Indeed, while triester may be larger in terms of having more electrons/dispersion forces, but using this explanation does not answer the question because that should mean triester will have higher melting point!

But for you, your major assumption was that the double bonds was cis. And in fact the part about the packing and cis double bond forming kinks is not under chemistry syllabus

AwkwardPotato SG

For the first question, i compared to strength of pdpd interaction vs hydrogen bond. Is that correct?

As for the c=c double bond qn, i rounded off my answer to 3? Will i be penalized?

For the reaction between NO2 and SO2 I used the data booklet so i ended up having So42- and N2 as the product instead? Is that wrong?

Ccii SG

What's the equation for CCl3-CHO + OH-?

Thefire521 SG

What's the equation for CCl3-CHO + OH-?

Gives u methanoate hco2- and chcl3 liquid that insolubles

Yes pdpd vs h bond

No so4 and n2 is wrong.

C=c double bond they asked for 3s.f. so anything that is not 3.s.f will minus 1

AwkwardPotato SG

I think i screwed up planning cause i only had like 15mins to write anD I WAS SO SLEEPY I COULDNT EVEN concentrate so i can barely read the qn wow!!! Oh but for planning is it right to use the calculated value which was like 4.6+g smth for the reaction? Btw what do the planning qn want i cant even remember cause i wasnt rlly awake.

Thefire521 SG

Please catch up on your sleep now so that you dont fall asleep for paper 3 as well

UltimaOnline SG

Thanks, Thefire521, for your willingness to help out with all the other students' queries. You're a private tutor or school teacher, not a JC student, correct? You said "haha no i setted the paper was just interested in the discussions of students sitting for my little test hahaha".

As to the concerns raised by alliance88 and houdini_00, I never claimed to be (in fact, I can assure you I'm *not*) speaking on behalf of Cambridge or MOE-SEAB regarding official grade boundaries. Afterall, the bell-curve is subject to the performance of the entire Singapore JC cohort, which I've no way of knowing. I'm only giving my opinion (for whatever it's worth) based on the relative difficulty of the paper, without considering the performance of the entire Singapore JC cohort.

I simply assumed (mistakenly, perhaps) it would be understood by everyone reading this thread, that I was just giving my own opinion, whatever it's worth, (similarly to how Bilahari Kausikan is not, and never claimed to be, speaking on behalf of the PAP government whenever he writes an opinion article) on how the A grade boundary might be swayed by the difficulty of the Paper, just as how many other private tutors and JC teachers would also give their own opinion on this matter, after each paper.

You're (not just alliance88 and houdini_00, but everyone else as well who feels likewise) welcome to ignore my future opinion posts on possible shifts on the A grade boundary, eg. after the upcoming P3 and P1, if you feel they're not useful or worse, discouraging.

Zhhh_ SG

if I forgot to x2 the Mr of Iodine, how many marks will I lose? my answer was 5.70 which was twice of 2.85. question was 4m.

Sir3 SG

Hi may i know why is so42- and n2 wrong? I wrote both eqns meaning one eqn produced so3 and n2o and the other produced so42- and n2... Will i get any marks

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