2014 H2 Chemistry Paper 2, Paper 3 and Paper 1 discussions

last SG · 2014-11-17T21:59:01+00:00

Guys I know this is a chem discussion page but can someone post their answers for Bio MCQ today? :S Think I'm gonna get 33/34 crying

Kingweixian SG

Can I say for 2diii) Can I say M is not chiral cos it is not bonded to 4 different substituent( 2 substituent are the same) since chiral concept is just whether if the compound is bonded to 4 diff substitient and the qn is 1m

UltimaOnline SG

Yes, that's correct.

Momento SG

Sir, may i ask whats the best way to study for paper 1

UltimaOnline SG

Sir, may i ask whats the best way to study for paper 1

Practice the 2010, 2011, 2012 and 2013 Singapore A Level Paper 1s, then all 20 JCs 2014 Prelim Paper 1s (or if you're short of time, the top 10 JCs Paper 1s).

moonwalkers SG

Hi,

1) For p2, can i check with you, if the graph drawn for the rate against time graph (in the presence of catalyst), if i drew it as a line which is steeper than the one w/o catalyst, but didn't plateau it, will I get 1m out of 2?

2) And also for the explanation of that graph draw, if i mention that adding catalyst will increase the rate constant, hence a steeper gradient because rate is now faster, but no mention about plateauing, will there be marks?

3) For p3, qn3a, if I mentioned the pts that I is a stronger reducing agent than Cl. And H2SO4 is a stronger oxidising agent than H3PO4, so if H2SO4 is used against I2, then it will be oxidised to HI, and further oxidised to I2 again which would contaminate HI.

With the eqns,

H3PO4 + NaI ---> HI + NaH2PO4

H2SO4 + NaI ---> HI + NaHSO4

2HI + H2SO4 ---> I2 + SO2 + 2H2O

how many marks do u think i can get?

4) For qn 1, about why H2O2 is more acidic than H2O, can i mention about H2O2 having an additional -OH electron withdrawing grp which stabilises its conjugate base so it being more acidic?

Thks!

rynal SG

the graph in P2 for reaction kinetics ah we were supposed to draw the new graph for enzyme-catalysed reaction on the one on the right which is a concentration/time graph and it thus its a steeper straight line rite? :P alot of my frens did the same thing too :P

UltimaOnline SG

For both Moonwalkers and Rynal, the correct answer for the enzyme catalyzed graph is :

Moonwalkers :

Q1 & 2 ) You'll get some marks, not full marks, but you'll get some marks. Exactly how many marks is impossible to say without looking at your exact submitted answer. But don't worry too much about this. Focus on your P1.

Q3) Your equations are correct, but (assuming what you submitted is what you posted) you lose marks for the following errors :
It's HI that's a stronger reducing agent than HCl, and not "I is a stronger reducing agent than Cl".
"The statement H2SO4 is used against I2, then it will be oxidised to HI, and further oxidised to I2 again which would contaminate HI" contains 2 errors :
firstly, the question describes H2SO4 being reacted with NaI, not I2; secondly, if I2 is converted to HI, then I2 is reduced to HI, not oxidized.

Q4) To be technically accurate, it should be an additional electronegative, inductively electron-withdrawing "O atom" rather than "OH group". Afterall the H is present in both conjugate bases, it is the 2nd O atom which is present in HOO- but not in HO-. Cambridge may or may not award you a mark for this.

Soft&Wet SG

Hi sir,do you have softcopies of past year A level h2 chem p1 paper?Are there any sources where i can find these papers?

UltimaOnline SG

Hi sir,do you have softcopies of past year A level h2 chem p1 paper?Are there any sources where i can find these papers?

For Singapore papers, there aren't any soft copies around. For UK 'A' levels, you can download them from http://www.xtremepapers.com/

student1996 SG

Hi, for paper 3 qn 3civ) is it possible to say that the p orbitals containing lone pair of electrons on Cl overlaps with the pi orbitals of the c=c, thus causing partial double bond formation and making it hard for the C-Cl bond to break?

moonwalkers SG

Thanks Ultima..

Oops i wrote wrongly about H2SO4 being used against I2, actually I meant H2SO4 being used against NaI, it would produce HI which would be further oxidised by H2SO4 to I2 which contaminates HI. But I think I carelessly wrote in my exam script that I is a stronger reducing agent than Cl, so maybe I would be deducted a mark for this?

For p3 q5, the effect of adding NH3 (before in excess) to Cu2+,

Its Cu2+ + 2OH- ---> Cu(OH)2 (reversible arrow), but if i didn't write the initial eqn of NH3 reacting with H2O to form OH-, will I be penalised?

And if i used LCP in the later part to explain why Cu(OH)2 ppt dissolves to form dark blue soln, but didnt use Ionic pdt < Ksp concept to explain why it dissolves, is it okay?

Thks!

UltimaOnline SG

Yes, that should be acceptable by Cambridge as well.

UltimaOnline SG

Thanks Ultima..

For p3 q5, the effect of adding NH3 (before in excess) to Cu2+,

Its Cu2+ + 2OH- ---> Cu(OH)2 (reversible arrow), but if i didn't write the initial eqn of NH3 reacting with H2O to form OH-, will I be penalised?

And if i used LCP in the later part to explain why Cu(OH)2 ppt dissolves to form dark blue soln, but didnt use Ionic pdt < Ksp concept to explain why it dissolves, is it okay?

Thks!

Yes, you'll lose a mark for it.

Yes, you'll be penalized. The hydrolysis equation is required.

Yes, that's fine. No worries.

moonwalkers SG

Kk thanks!

Can I know why you think the cut off for A last year was 75%?

And do you think its possible for me to get an A this year if i got a range between 72-75%?

UltimaOnline SG

Kk thanks!

Can I know why you think the cut off for A last year was 75%?

And do you think its possible for me to get an A this year if i got a range between 72-75%?

I can't divulge the full reasons here, but I certainly have good reasons for my confidence that this year's cut-off grade will be 75% (barring a much-easier-than-expected or a much-tougher-than-expected P1, which is very unlikely).

If you're right about your final % score, then you'll stand a fair (depending on your final exact % score) chance of getting an A grade this year.

Kingweixian SG

Can I ask what’s the answer for 2a, 2b and 2ci for p3
cos I not sure if I correct a not

UltimaOnline SG

Can I ask what’s the answer for 2a, 2b and 2ci for p3
cos I not sure if I correct a not

-914, -116.5, +0.1045

littledragon SG

hello, could someone could give me a weightage or rough weightage for each paper?
so far what i know is that planning is 5%, SPA is 15%.. so how would p1,2,3 fit the remaining 80%?

this comes after much regretted paper 3 during which my mind went blank upon seeing weird qns like heating LiAlH4 would make it a stronger reducing agent etc... i might not have done so well for that :X

so.. id love to know how much paper 3 would have screwed my overall score over so i can better prepare myself for how much p2 and 1 can pull me up..

Alohamadda SG

if for qn 2b) i quoted -116.5 as -117 (3sf) as final answer, will deduct?

The Code SG

A Level Chemistry Paper 2 Planning Practice : http://twig.sg/facebook/Paper 2 Planning.pdf

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