2014 H2 Chemistry Paper 2, Paper 3 and Paper 1 discussions
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This thread is for 2014 H2 Chemistry Paper 2, Paper 3 and Paper 1 discussions.
I may make comments on the questions and answers after each Paper. A level students are welcome to post here in this thread, with their queries to check their own answers after each paper.
For starters, as you have only 1 day left before Paper 2, you may wish to revise the entire H2 Chemistry syllabus using the many excellent summary notes, tables and mindmaps for H2 Chemistry that are free-to-download (you just need to use your Facebook account to login) from Owlcove.sg ( http://owlcove.sg/ ).
Lastly, remember to get at least 8 hours of sleep the night before each A level paper, and also be sure to have a very light meal (just enough to supply sufficient glucose to your brain for the 2 hour duration) just before each paper, for only then will you be capable of performing your personal best. -
For those who are interested, the A grade threshold for H2 Chemistry is approximately 75%, give or take 1-3 % based on the bell-curve for the cohort.
So if this year's Papers 2, 3 and 1 are ridiculously easy, it may take up to 78% to score an A grade. Likewise and conversely, if this year's Papers 2, 3 and 1 are ridiculously tough, it may take as low as 72% to score an A grade.
Which scenario would you prefer? ;Þ -
What is your take for planning this year? I prefer 75%,balanced one
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Originally posted by a mugger:
What is your take for planning this year? I prefer 75%,balanced one
My personal take is, don't bother trying to predict Planning. Every year for the past 4 years, all 20 JCs fail spectacularly at predicting Cambridge's Planning question.
Regardless, those of you who are JC students, if your JC predicted any Planning question for this year, feel free to share it here for Mugger and all your fellow students?
Then 75% for A grade it is. If this year's papers are similar in difficulty to last year's papers. -
The cut-off score to get A grade in the Korean CSAT (A Level equivalent) Mathematics paper is 100%! Just 1 mark gone (even if it's just 0.1% of overall score), and there goes your A grade! Lol!
http://news.asiaone.com/news/education/easy-exam-adds-confusion-college-admission -
Originally posted by UltimaOnline:
The cut-off score to get A grade in the Korean CSAT (A Level equivalent) Mathematics paper is 100%! Just 1 mark gone (even if it's just 0.1% of overall score), and there goes your A grade! Lol!
http://news.asiaone.com/news/education/easy-exam-adds-confusion-college-admission
i wonder what is the number of students getting an A? -
For Korean CSAT, ask the Koreans.
For A Level H2 Chemstry, the overall % of students scoring an A grade is always somewhere between 20% to 30% (varies with each year; the bell-curve is not a absolute inflexible one, but only a relative modifier). The 'worst' JC has approximately 1% of students scoring A, while the 'best' JC has approximately 70% of students scoring A. -
Can help me take a look please :
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If the question allows condensed formula for optical isomers, then it's true you cannot write "H3CH2C-" but you must still write as "CH3CH2-". But if the Cambridge question requires "displayed structural formula" meaning you must show all the individual bonds, then you should really draw out both optical isomers exactly as if they were mirror images, eg. if LHS optical isomer shows -O-H, the RHS optical isomer should show H-O-.
Cambridge accepts either formal charges on the individual atoms, or overall ionic charge outside the square brackets (which represents "summation" of individual formal charges). But for dot-and-cross diagram, don't show formal charges, just only show the overall ionic charge outside the square brackets, as the positive formal charge looks too similar to a cross. -
Q1. How did *you* find today's P2? ( Easy / Normal / Hard )
Q2. How did your *school mates* find today's P2? ( Easy / Normal / Hard ) -
If Cambridge had asked "How many isomers in total? Draw all of them." Then almost no Singapore student would be able to get full marks. There are 8 stereoisomers in total.
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Hi
If i drew 4 isomers, still got marks?
And how to explain the reaction of aq br2 and the alkene provided? With respect to mechanism
And why must use naoh to remove acidified phenylamine if not no reaction can take place?
And how much to get A? Everyone say easy, so hard for me....
Thx sirr
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Yes, you should get full marks for drawing 4 isomers (either two sets of optical isomers, or 1 set optical isomer and 1 set geometrical isomers).
- Tertiary carbocation more stable (since alkyl groups are electron donating by induction).
- H2O is the competing nucleophile (present in higher molarity than Br-)
- After H2O nucleophile adds onto carbocation intermediate, deprotonation generates the final product of bromoalcohol.
The immediate product is phenylammonium chloride, which is ionic and hence difficult to seprate. Hence deprotonation is required to separate the molecular phenylamine via steam distillation.
Based on P2 alone, an A grade should still be approximately 75%. -
Do u think its difficult sir?
And if i stupidly wrote the wrong units for rate constant but value correct, 2 marks get 1 mark?
And why is fes2 yellow gold color?
And what are the reagents and conditions for the last part of last qn?
Thx sir i am very worried...
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Originally posted by Alohamadda:
Do u think its difficult sir?
And if i stupidly wrote the wrong units for rate constant but value correct, 2 marks get 1 mark?
And why is fes2 yellow gold color?
And what are the reagents and conditions for the last part of last qn?
Thx sir i am very worried...
Difficulty is same as last couple of years. So A grade cut-off score should still be approx 75%.
Yes you get 1 mark.
Same answer as why transition metal compounds are often coloured. You must specify that the disulfide ion functions as a ligand here.
HCl(g), followed by *excess* concentrated ethanolic NH3, heat in sealed tube.
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Need to write excess nh3?
This is my answer: excess con nh3 dissolved in alcohol, heat in sealed tube? I no specify alcohol
Can sir?
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Hi Ultima, thanks for taking the time to respond to our queries with regards to today's paper. Got a question for you too, hope you don't mind.
If I recall correctly, there was a question asking for the graphical relationship between rate of enzyme-catalysed reaction and concentration of CO2 (aq). My answer was a steeper but concave downwards curve followed by a straight line with the same gradient as the previous answer, which I believe was a straight line with a positive gradient if I'm not wrong. Something like a rate of reaction against concentration of substrate curve, just without the plateau. My understanding is that the x-axis was concentration of CO2, and not the enzyme/substrate, hence my answer, but I've observed that many others drew the same curve with a plateau. Hopefully you can clarify my doubts!
Have a nice day all. :)
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Originally posted by Alohamadda:
Need to write excess nh3?
This is my answer: excess con nh3 dissolved in alcohol, heat in sealed tube? I no specify alcohol
Can sir?
Alohamadda, yes you're right, it needs to be "excess". No need to specify "ethanol", just "alcohol" will do. In fact, many students didn't even mention ethanolic/alcoholic solvent. These students may or may not be penalized (Cambridge Mark Scheme does vary a little between different years). -
Originally posted by Temporary212:
Hi Ultima, thanks for taking the time to respond to our queries with regards to today's paper. Got a question for you too, hope you don't mind.
If I recall correctly, there was a question asking for the graphical relationship between rate of enzyme-catalysed reaction and concentration of CO2 (aq). My answer was a steeper but concave downwards curve followed by a straight line with the same gradient as the previous answer, which I believe was a straight line with a positive gradient if I'm not wrong. Something like a rate of reaction against concentration of substrate curve, just without the plateau. My understanding is that the x-axis was concentration of CO2, and not the enzyme/substrate, hence my answer, but I've observed that many others drew the same curve with a plateau. Hopefully you can clarify my doubts!
Have a nice day all. :)
Hi Temporary212,
Kinetics transits from 1st order to zero order (ie. the plateau) when all the active sites of the limited amount of enzyme is used up.
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Hello sir, last one...
For the first part of first qn, what ish the answer? Is na included?
And how are they marking for the c=c bond orbital qn?
Tq
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Originally posted by Alohamadda:
Hello sir, last one...
For the first part of first qn, what ish the answer? Is na included?
And how are they marking for the c=c bond orbital qn?
Tq
First part of first qn (Planning) is simply H+(aq) + OH-(aq) --> H2O(l)
Combine the details of these 3 diagrams :
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Hi , I would like to ask how did the ph of the co2 change when exposed to air? And for the planning if I wrote out the full equation for the including spectator ions it is correct? Lastly for the mechanism do I just have to draw or do I have to include words to for the last qns , and how does the isomer looks like ?
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Originally posted by Littleblackdot:
Hi , I would like to ask how did the ph of the co2 change when exposed to air? And for the planning if I wrote out the full equation for the including spectator ions it is correct? Lastly for the mechanism do I just have to draw or do I have to include words to for the last qns , and how does the isomer looks like ?
Position of equilibrium for all 3 reactions shifts to the LHS. Hence pH increases.
No, spectator ions not allowed.
Both mechanism and textual explanation (see my post earlier in this thread) required for full marks.
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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?
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Shouldnt rhs be favored since co2(g) increase in the air?