2017 H2 Chemistry JC1 & 2 students post your questions here
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Originally posted by UltimaOnline:
A BedokFunland JC H2 Chemistry Challenge
99% of Singapore JC students will get this wrong, and about 50% of private tutors and school teachers will get this wrong.
Calculate the pH of 1.0 x 10^-8 mol/dm3 of HNO3.
Go ahead and calculate it, and if you like, post your final answer here to 3 decimal places (note : don't show your working, coz in case you get it right, don't ruin the fun for others). I'll only state if your final ans is correct or wrong, nothing more nothing less.
Is ph=6.96 to 3 sf?
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Originally posted by MapPwner:
Is ph=6.96 to 3 sf?
Good attempt. While not the A grade answer, at least it's not the U grade answer. I know you don't have a private tutor, so try asking your school teacher? But don't be shocked to find out that most JC school teachers and private tutors will also give the same answer you did.Assuming you'll like to try again (eg. after asking your school teacher), only post the correct final answer here, and don't post the correct working (as it'll ruin the fun for others).
And I can't give any hints, because it's impossible to give any hints without giving away the correct working and hence answer.
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So it wasn't the lychee fruit per se that caused the acute encephalitis deaths afterall, but the insecticide used.
Insecticide responsible for deaths of 13 children in Bangladesh: study
https://sg.yahoo.com/news/insecticide-responsible-deaths-13-children-bangladesh-study-004100050.html
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My BedokFunland JC H2 Chemistry Challenge Question :
Q1. Draw the full electron-flow curved-arrow reaction mechanism for every step of the synthesis pathway :
Cyclopentadiene -----> Octachlorocyclopentane -----> Hexachlorocyclopentadiene -----> Endosulfan alcohol -----> Endosulfan
Q2.
a) Explain why α-Endosulfan is obtained as a racemate.
b) Explain why β-Endosulfan is a meso molecule.
c) Suggest why α-Endosulfan is the more thermodynamically stable of the two isomers.
d) Suggest why the conversion of β-Endosulfan to the α isomer is irreversible.
e) Suggest why the conversion of β-Endosulfan to the α isomer is slow.
https://en.wikipedia.org/wiki/SNi
http://www.masterorganicchemistry.com/2014/02/10/socl2-and-the-sni-mechanism/Q3.
The chlorination of secondary alcohols with PCl5 results in an inversion of configuration, but when SOCl2 is used, the product could possess either a retention or inversion of configuration, as shown in the diagram above.a) Explain why addition of pyridine to the SOCl2 reaction results in the inversion of configuration.
b) Use of SOCl2 in either a non-nucleophilic solvent, or in dioxane (a nucleophilic solvent), for reaction with secondary alcohols, both result in the retention of configuration in the final product, but this retention is accomplished by 2 contrasting mechanisms. Explain these 2 contrasting mechanisms and why both result in the retention of configuration in the final product.
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Just want to ask what is your take on the difficulty of SAJC H2 Chem P2/P3 2013 Prelim Paper?Is it considered equivalent to A level standard or slightly harder?Other than the (killer) purification and synthesis question in p2 and excluding the planning question(since its in p4 now instead) and also careless mistakes after checking answers,I feel that the paper is actually rather simple even though it looks tricky.
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Originally posted by MapPwner:
Just want to ask what is your take on the difficulty of SAJC H2 Chem P2/P3 2013 Prelim Paper?Is it considered equivalent to A level standard or slightly harder?Other than the (killer) purification and synthesis question in p2 and excluding the planning question(since its in p4 now instead) and also careless mistakes after checking answers,I feel that the paper is actually rather simple even though it looks tricky.
You're right that the 2013 SAJC paper is more or less A level standard. Whether it's slightly tougher or not depends on which year of the A level exams that you're comparing with. I expect this year's A level exam to be more or less that of the 2013 SAJC papers standard. I'll be surprised if the A level paper is any easier or any tougher than 2013 SAJC papers. -
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i love chem
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I love chem
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i love chem
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Just asking again about another thing.For a student which has just finished learning Transition Elements/Metals Chapter and attempting TYS question 2008/P2/Q4,which is me in this case,is it normal not being able to understand most of the question,which are mainly part C and D?
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Originally posted by MapPwner:
Just asking again about another thing.For a student which has just finished learning Transition Elements/Metals Chapter and attempting TYS question 2008/P2/Q4,which is me in this case,is it normal not being able to understand most of the question,which are mainly part C and D?
Indeed, this is one topic that Cambridge can set more challenging questions (especially for new syllabus), that can be used to distinguish A grade students from the rest of the cohort. Because this topic is so vast, that different JCs will expose different students to different coordination complexes, colors and geometries, as well as extension applications such as Kstab.So evidently this topic, together with solubility equilibria, are your Achilles heel. And guess what, Cambridge can set challenging (ie. A grade) questions combining coordination complexes with solubility equilibria, eg. Kstab + Ksp. Your Achilles heel combo! *evil laugh*
But don't worry lah, you don't need to outrun the bear, you just need to outrun your peers on the bell-curve, if you can't do the question, then likely (have confidence in yourself) that the majority of the national H2 student cohort also can't do.
Back to the TYS qn : the more exposed you are a greater number of coordination complexes (ie. various metal cations coordinated with various ligands), their geometries and colors, etc, the better equipped you'll be when Cambridge asks such questions, testing your exposure to the depth of this topic.
If there's any specific part of the question that you have a query regarding the given answer (either provided by your school or a TYS publisher), go ahead and ask me on the forum.
Not just MapPwner, but all 2017 JC students, anything you don't understand about a TYS qn or Prelim qn, go ahead and quote the source, eg. 2016 RJC P2 Q3, and specify what about the answer that you don't understand or agree with.
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Haha yeah I feel that transition metals(i feel overtime this chapter should be easy) and Ksp(content/understanding still so-so) to me for now are 2 daunting chapters.
But otherwise,I feel that other chapters which I have little difficulty in should be beneficial to me in scoring for other components of the paper.Based on 2008 TYS paper,P3 and P2 except for transition metals,questions involving other chapters to me seem like free marks,so relatively easy to score near full marks/full marks for that question.
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Originally posted by MapPwner:
Haha yeah I feel that transition metals(i feel overtime this chapter should be easy) and Ksp(content/understanding still so-so) to me for now are 2 daunting chapters.
But otherwise,I feel that other chapters which I have little difficulty in should be beneficial to me in scoring for other components of the paper.Based on 2008 TYS paper,P3 and P2 except for transition metals,questions involving other chapters to me seem like free marks,so relatively easy to score near full marks/full marks for that question.
I've got a cool idea on how to help you out here.Go compile all the toughest Transition Metal and Solubility Equilibria questions you can find from all the TYS and Prelim Papers from the last 10 years, focusing inordinately on (the toughest questions from) these 2 topics (after all, you're only as strong as your weakest link, these 2 topics are your limiting reactants), and whatever you don't understand about the question and/or the given answers / solutions / mark schemes, post your query here and I'll give my comments.
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Originally posted by UltimaOnline:
I've got a cool idea on how to help you out here.Go compile all the toughest Transition Metal and Solubility Equilibria questions you can find from all the TYS and Prelim Papers from the last 10 years, focusing inordinately on (the toughest questions from) these 2 topics (after all, you're only as strong as your weakest link, these 2 topics are your limiting reactants), and whatever you don't understand about the question and/or the given answers / solutions / mark schemes, post your query here and I'll give my comments.
I will try to compile them all when I'm free while doing my revision for chemistry.I think for transition metals the reason why I couldn't do that question was because I didn't read my notes thoroughly to deduce the unknown colourless compound to be [CuCl2]-,as d-orbital splitting resulting in d-to-d electronic transition to form coloured compounds only occurs if the transition metal ion has partially filled 3d orbitals .In this case Cu(I) has fully filled 3d orbitals thats why it is colourless.
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i love chem
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Can I ask something about H2 chemistry question from VJC Prelim 2011/P3/Q4(b) on organic deductive on C10H8O2,which is a neutral compound.
In determing the structure of D,my answer was C6H6-C(carbon 1 of benzene ring)H=C(CH3)COO-(bond bonded back to carbon 2 of benzene ring),resulting in structure having 1 benzene ring and 1 6 membered cyclic ring suiting the formula and subsequent reactions.But the answer given was 1 benzene ring and 1 5 membered cyclic ring whereby the C=C bond was placed outwards of the 5 membered cyclic ring.
Is my answer considered wrong as my 6 membered cyclic ring structure will lead to bond-angle strain making the structure unstable?Or is it acceptable?
Also,just asking is this question considered difficult?
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Originally posted by MapPwner:
Can I ask something about H2 chemistry question from VJC Prelim 2011/P3/Q4(b) on organic deductive on C10H8O2,which is a neutral compound.
In determing the structure of D,my answer was C6H6-C(carbon 1 of benzene ring)H=C(CH3)COO-(bond bonded back to carbon 2 of benzene ring),resulting in structure having 1 benzene ring and 1 6 membered cyclic ring suiting the formula and subsequent reactions.But the answer given was 1 benzene ring and 1 5 membered cyclic ring whereby the C=C bond was placed outwards of the 5 membered cyclic ring.
Is my answer considered wrong as my 6 membered cyclic ring structure will lead to bond-angle strain making the structure unstable?Or is it acceptable?
Also,just asking is this question considered difficult?
Your fatal error (ie. why your alternative answer will not be accepted by Cambridge), is that your E (unlike VJC's answer) is not capable of geometric isomerism, as your double-bond is within a 6 membered-ring.This question is of average difficulty for an upper tier JC such as VJC (for upper tier JC prelim papers, there have been many deductive elucidation questions much tougher than this), so this question would be considered slightly difficult for mid tier JC, and rather difficult for lower tier JCs and MI. Cambridge A level questions should be of this difficulty or slightly easier, but anything is possible.
For yourself, I expect you didn't have any difficulty solving this question, so you prolly found this easy, except that your answer is wrong, and Cambridge would award you with some credit, exactly how much depends on the question (whether deductions are required or only final elucidations), and how you presented your answer.
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Originally posted by UltimaOnline:
Your fatal error (ie. why your alternative answer will not be accepted by Cambridge), is that your E (unlike VJC's answer) is not capable of geometric isomerism, as your double-bond is within a 6 membered-ring.This question is of average difficulty for an upper tier JC such as VJC (for upper tier JC prelim papers, there have been many deductive elucidation questions much tougher than this), so this question would be considered slightly difficult for mid tier JC, and rather difficult for lower tier JCs and MI. Cambridge A level questions should be of this difficulty or slightly easier, but anything is possible.
For yourself, I expect you didn't have any difficulty solving this question, so you prolly found this easy, except that your answer is wrong, and Cambridge would award you with some credit, exactly how much depends on the question (whether deductions are required or only final elucidations), and how you presented your answer.
Ah I see,no wonder.My peers found it difficult though.
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So other organic deductive questions such as AJC Prelim 2012/P3/Q3(b) are considered average difficulty to top JCs but slightly hard for mid/lower-tiered?I found the AJC prelim deductive qn simple though,simple as in able to elucidate the expected structure without even writing anything on paper to deduce.The VJC one was somewhat harder as i spent some time placing the c=c bond all over the place.
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Originally posted by MapPwner:
So other organic deductive questions such as AJC Prelim 2012/P3/Q3(b) are considered average difficulty to top JCs but slightly hard for mid/lower-tiered?I found the AJC prelim deductive qn simple though,simple as in able to elucidate the expected structure without even writing anything on paper to deduce.The VJC one was somewhat harder as i spent some time placing the c=c bond all over the place.
The VJC and AJC questions are very similar, except that, as you say, the VJC question is slightly tougher because of the double bond. So this particular AJC question is considered slightly below average difficulty for top tier JCs, and approximately average difficulty for medium tier JCs.Btw, since you've evidently no problems solving OC questions, how about focusing more on Ksp & TM questions?
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I actually am doing Ksp,TM questions currently from other JC prelim questions at my own free time and currently the questions i encountered are relatively manageable for now.Only asked about this particular organic deductive question because it was part of my school's set of banded lecture questions,which is part of the band 1 lecture questions.My school ranks students into 4 bands,band 1 being the best and band 4 being the worst and the questions provided for each band varies.
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Originally posted by MapPwner:
I actually am doing Ksp,TM questions currently from other JC prelim questions at my own free time and currently the questions i encountered are relatively manageable for now.Only asked about this particular organic deductive question because it was part of my school's set of banded lecture questions,which is part of the band 1 lecture questions.My school ranks students into 4 bands,band 1 being the best and band 4 being the worst and the questions provided for each band varies.
Surely your band1 questions include tougher OC deductive elucidation questions than the VJC and AJC questions? If not, don't just rely on your school's compiled questions, go obtain for yourself (and do them!) all the Prelim papers from the last 5 years at least (eg. you can buy them online) to challenge yourself.And of course, seeing how your OC mastery is already top of your JC, I'm more interested in you sharing tough Ksp and TM questions that you struggle with.