2014 H2 Chemistry Paper 2, Paper 3 and Paper 1 discussions
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So if i get my structure of C wrongly, which obviously means I got the structure of A wrongly too cause it will be derived from C.. then do u think there will be ecf for my structure of A?
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Originally posted by moonwalkers:
So if i get my structure of C wrongly, which obviously means I got the structure of A wrongly too cause it will be derived from C.. then do u think there will be ecf for my structure of A?
Yes, fortunately for you, Cambridge does allow for error carried forward in Deductive Elucidation questions. -
Is there any instance where a student screwed up one of his SPA but did well eventually? (Screwed up as in getting anomalous results for titration)
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Originally posted by Kingweixian:
Is there any instance where a student screwed up one of his SPA but did well eventually? (Screwed up as in getting anomalous results for titration)
Can. As long as you passed your SPA (ie.>50%), and you do very well (ie.>85%) for all your remaining papers, still can get A (ie. overall 75%), based on the weightages (see page 4 below) :
https://www.seab.gov.sg/content/syllabus/alevel/2015Syllabus/9647_2015.pdf -
Sir, for 3d ii) can i use the empirical formula of S?
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Originally posted by Adelineeeee (::
Sir, for 3d ii) can i use the empirical formula of S?
No, it must be the molecular formula. But if everything else about your equation is correct, you'll still get 1 mark out of 2. -
Originally posted by UltimaOnline:
Can. As long as you passed your SPA (ie.>50%), and you do very well (ie.>85%) for all your remaining papers, still can get A (ie. overall 75%), based on the weightages (see page 4 below) :
https://www.seab.gov.sg/content/syllabus/alevel/2015Syllabus/9647_2015.pdfBased on syllabus
Grading Conditions
Candidates’ results are based on the aggregation of their marks in the various papers, i.e. there are no hurdle conditions under which a prescribed level of performance in an individual paper prevents the award of an A level result.
In fact, you still can get an A if you failed SPA, but that will mean a near perfect P1 - P3.
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Technically true, but also all that much more difficult to pull off, so I didn't want to say so.Originally posted by SBS n SMRT:
Based on syllabus
Grading Conditions
Candidates’ results are based on the aggregation of their marks in the various papers, i.e. there are no hurdle conditions under which a prescribed level of performance in an individual paper prevents the award of an A level result.
In fact, you still can get an A if you failed SPA, but that will mean a near perfect P1 - P3.
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SIr, how about 3b ii) ? Can i say that Phosphorous has empty low lying 3d orbitals and hence can accomodate the H20 in moist air?
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Originally posted by Adelineeeee (::
SIr, how about 3b ii) ? Can i say that Phosphorous has empty low lying 3d orbitals and hence can accomodate the H20 in moist air?
No. Because this question isn't asking you to compare a period 2 vs a period 3 element in the context of susceptibility to hydrolysis. -
Sir
How to form pcl3 and how to purify it? From qn 3
Thz
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Originally posted by Alohamadda:
Sir
How to form pcl3 and how to purify it? From qn 3
Thz
http://en.wikipedia.org/wiki/Phosphorus_trichloride#Preparation -
Hi sir, i would like to know the answer for question 1(b)
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Ok thanks.
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Originally posted by Momento:
Hi sir, i would like to know the answer for question 1(b)
Just straightforward calculations. Final answer ratio is 3.57 -
To elaborate on Q3c(iv) and Q1d(ii), both questions having a related theme of "ring strain due to angle strain", the answer (for Q3) requires mention of of "triply bonded C atoms are ideally sp hybridized" and "sp hybridized C atoms have 180 deg (for Q3)" or "sp3 hybridized C atoms have 109.5 deg (for Q1)" which "deviates significantly from bond angles within the ring (in Q3 & Q1)" and that due to this "angle strain" or "ring strain" as a result of "inter-electron repulsion", therefore (for Q1) "strained bonds break more easily" or "bond dissociation enthalpy is less endothermic".
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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
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Originally posted by Kingweixian:
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
Yes, that's correct. -
Sir, may i ask whats the best way to study for paper 1
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Originally posted by Momento:
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). -
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!
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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
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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. -
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?
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Originally posted by Soft&Wet:
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/