2014 H2 Chemistry Paper 2, Paper 3 and Paper 1 discussions
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Originally posted by AlexSummers:
Hi Sir. I screwed up the planning question... I didnt use a styrofoam cup and plotted the wrong graph... plus I didnt finish the plan after plotting the graph (ie calculations)... will it be detrimental to my overall?
No worries, that's just a couple of marks penalized, so you'll still pass your Planning question, which as long as combined with a high A grade performance for the rest of P2 qns, as well as P3 and P1, still can yield an overall A grade (which should be approx. 75%). -
Originally posted by Littleblackdot:
Shouldnt rhs be favored since co2(g) increase in the air?
No, position of equilibrium shifts to LHS, since [CO2] decreases, because atmospheric [CO2] is much lower than [CO2] in a bottle of carbonated drink.
http://en.wikipedia.org/wiki/Atmosphere_of_Earth#Composition -
Hi Sir,I would like to ask about the question reguarding the 99% question(can't remember the details exactly).Is it 0.99=0.5^t/ln2 or 0.01=0.5^t/ln2?
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Originally posted by Soft&Wet:
Hi Sir,I would like to ask about the question reguarding the 99% question(can't remember the details exactly).Is it 0.99=0.5^t/ln2 or 0.01=0.5^t/ln2?
The formula is for reactant. The question specified 99% for product. So it should be 1% for reactant. -
Hmm how abt the first part of second qn?
Do we rlly require to write out the chunks of words for the electrophilic addition?my sch says its no needed though....
And is 53 an A? my frens scoring 65s and 66s.. School teachers saying its more likely towards low 80 spectrum this yr. Sadssss
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Originally posted by Alohamadda:
Hmm how abt the first part of second qn?
Do we rlly require to write out the chunks of words for the electrophilic addition?my sch says its no needed though....
And is 53 an A? my frens scoring 65s and 66s.. School teachers saying its more likely towards low 80 spectrum this yr. Sadssss
What's required is not a textual description of electrophilic addition per se, but rather "stability of tertiary carbocation due to inductive effect", and "competing H2O nucleophile (present in higher concentration compared to Br-) attacking the carbocation intermediate". But even if you didn't write the above ideal model answer, you may still get full marks or close to full marks. No worries.
I'm talking about cut-off percentages for A grade, not raw score. And don't you listen to school teachers, they talk a lot of rubbish and BS. Cut off (overall) % to get A grade (as it stands, assuming P3 and P1 are of similar difficulty as last year) will be approximately 75%. If the upcoming P3 and P1 turn out to be tougher than last couple of years, it may decrease to as low as 72%. -
Ok thx sir for ur kind help. Will come back here hopefully with lesser queries on wednesday
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Originally posted by Alohamadda:
Ok thx sir for ur kind help. Will come back here hopefully with lesser queries on wednesday
No prob at all. Remember to choose your 4 Qns wisely for P3! Have fun! ;Þ -
Hi Ultima, got two questions for you, hope you don't mind.
For planning I did thermometric titration like the one in Wikipedia whereby you do titration and measure end point through temperature instead of volume. But all my friends say must keep volume constant which is not possible for thermometric titration. Are they wrong or am I missing something. If I am not wrong, the Qns did ask us to do that right.
As for the catalysed reaction rate graph, shouldn't it be a steeper straight line graph? Cause it is not a biological catalyst(I think so, I forget the Qns already).
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Originally posted by Ifaileverything:
Hi Ultima, got two questions for you, hope you don't mind.
For planning I did thermometric titration like the one in Wikipedia whereby you do titration and measure end point through temperature instead of volume. But all my friends say must keep volume constant which is not possible for thermometric titration. Are they wrong or am I missing something. If I am not wrong, the Qns did ask us to do that right.
As for the catalysed reaction rate graph, shouldn't it be a steeper straight line graph? Cause it is not a biological catalyst(I think so, I forget the Qns already).
The procedure described in Wikipedia is right, don't let your friends make you worry.
http://en.wikipedia.org/wiki/Thermometric_titration
And don't worry about losing a coupe of marks here and there for Planning. In fact, even if you totally skip the entire planning question but as long as you get all other questions in P2, P3 and P1 (almost) all correct, you can still get your A grade. No worries.
Actually the question *did* specify the catalyst was an enzyme. No worries lah. As long as your graph looks something like this one can liao.
If these are your main worries from P2, it means you probably can get a high A grade (ie. > 80%) for P2. As I already said earlier in this thread, overall cut-off % to get A will be approx 75%. Just don't screw up P3 and P1, and you should get your A no probs. -
So how did you guys find P3? Easy / Normal / Hard?
Which question did you not do? -
I did 2,3,4,5
For q3)c(iv) how do ah?
And for last qn, i kinda didnt label qn part f though...
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Originally posted by Alohamadda:
I did 2,3,4,5
For q3)c(iv) how do ah?
And for last qn, i kinda didnt label qn part f though...
A triply bonded C atom ideally (ie. for maximum stability) needs to be sp hybridized, ie. 180 degrees bond angle. Hence, the cycloalkyne cannot be formed, as it would suffer from extremely severe ring strain due to angle strain. -
How about the labeling of qn? Will deduct marks anot?
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Originally posted by Alohamadda:
How about the labeling of qn? Will deduct marks anot?
No worries. -
What if i juz wrote bond strain as angle between ctriplec is unexpected without stating angle?
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I did 1,2,4,5... but I regretted doing 2... Is it suppose to be difficult? i no longer know how to gauge anymore...
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Originally posted by Alohamadda:
What if i juz wrote bond strain as angle between ctriplec is unexpected without stating angle?
Hard to say for sure. No worries. Explanation is just 1 mark. -
Originally posted by AlexSummers:
I did 1,2,4,5... but I regretted doing 2... Is it suppose to be difficult? i no longer know how to gauge anymore...
All 5 qns are pretty balanced. No all-easy or all-hard question. Depends on individual proficiency of topics. -
Hi
Is is possible to come up with a suggested answer key? Haha. Sorry to troubleu
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Hi. I personally find paper 3 to be not easy especially the reactions (eg q5) and I am not quite confident after doing the paper. May I know whats the chance of obtaining a B if I couldn't quite attempt the planning but found the rest of p2 manageable, found p3 relatively tough and couldn't complete some parts here and not confident of many answers and there amounting to at least 20 marks. Thank you
PS: can anyone tell me how they think they fare/find the paper?
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Originally posted by Alohamadda:
Hi
Is is possible to come up with a suggested answer key? Haha. Sorry to troubleu
No sorry, but I'm sure many JC teachers and some other tuition teachers will shortly come up with a Solutions document that you can find online and download it. Meanwhile, if you've a couple of specific questions you want to check your answer, you can post them here and I'll give my comments. -
Sir
Last qn, what are the steps for the 3 org chem qns in qn 4?
Tq
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Originally posted by alycx:
Hi. I personally find paper 3 to be not easy especially the reactions (eg q5) and I am not quite confident after doing the paper. May I know whats the chance of obtaining a B if I couldn't quite attempt the planning but found the rest of p2 manageable, found p3 relatively tough and couldn't complete some parts here and not confident of many answers and there amounting to at least 20 marks. Thank you
PS: can anyone tell me how they think they fare/find the paper?
Don't worry about other students or Singapore JC teachers saying stuff like, "Wah, P2 and P3 all so easy! This time A grade cut-off will be over 80% liao!"
That's rubbish and bullshit. First of all, don't trust school teachers. Secondly, although many students will like to think that P2 and P3 are "soooo easy! Haha!" but frankly their answers may be not totally correct (especially since I personally disagree with many answers taught by Singapore JC school teachers, particularly in the context of the more challenging questions in this year's P2 and P3).
I cannot predict for you, since I have not read your submitted answers. But all I can say is, this year's H2 Chem papers are of the same difficulty as the last few years' H2 Chem papers, and as such the cut-off score for A grade will (almost definitely) remain at 75%. -
Originally posted by Alohamadda:
Sir
Last qn, what are the steps for the 3 org chem qns in qn 4?
Tq
i) H2O/H+, heat under reflux
KMnO4/H+, heat under reflux
ii) H2O/H+, heat under reflux
KMnO4/H+, heat under reflux
iii) KMnO4/H+, heat under reflux
warm with alkaline aqueous iodine, followed by acidification