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BedokFunland JC's A Level H2 Chemistry Qns (Part 2)

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    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    12,749 posts since May '05
    • [Medicine / H2 Biology] - https://en.wikipedia.org/wiki/Thalassemia

      [China] - Father brings little daughter to play inside grave everyday, because he can no longer afford her expensive medical bills for her severe thalassemia, and hopes this will get her used to the grave so she won't be frightened when she dies soon.

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      http://stomp.straitstimes.com/singapore-seen/dad-in-china-takes-sick-2-year-old-daughter-to-grave-to-play-for-heartbreaking-reason

    • [Chemistry / Medicine] - Be careful. There is some unidentified chemical species in A&W Root Beer that gives some people (not sure if you're one of them? just drink up to find out) a terrible instant-onset long-lasting migraine / headache that panadol & aspirin can't help with. In comparison, the only other brand available in Singapore, Mug Root Beer, doesn't cause headaches. So it's not Root Beer per se, but the A&W brand which is problematic.

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      http://mothership.sg/2017/07/aw-confirms-return-to-spore-in-2018/

    • Apparently, very few, if any at all, Singapore JC students (even with the help of their private tutors and school teachers) are able to solve this excellent Vietnamese question, so I'll be gracious and give you the following hints : mathematically (based on the data provided in the question) there are infinite possible solutions, thereafter based on the periodic table you can narrow this down to only a few possible solutions, thereafter applying your knowledge and understanding of Chemistry, you can further narrow this down to only 1 possible solution, ie. the correct answer.

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    • Taiwan : http://wenr.wes.org/2016/06/education-in-taiwan

      Indonesia : https://link.springer.com/article/10.1007/BF00598171

      Malaysia : http://multilingualmania.com/english-or-national-language-thoughts-from-malaysia/

      Hong Kong : http://www.scmp.com/lifestyle/family-education/article/1583037/argument-continues-over-using-cantonese-or-putonghuaM

      Are you kidding? The best language of instruction (eg. when learning Chemistry, Physics, Biology, Medicine, etc) is obviously English, the lingua franca of the world, in order to effectively communicate with the rest of the world (ie. not just with America ; for instance in Europe, the many different Europeans all have their own distinct mother tongue language, but almost all are at proficient in English for the sake of communication with the rest of the world). Having English as the language of instruction has conferred the single most important educational advantage Singapore has had over other Asian countries (eg. Malaysia, Indonesia, Taiwan, Hong Kong, etc), and as Singapore's bilingual policies have proven, does not necessarily require sacrificing your mother tongue or ethnic culture altogether.

    • 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.

      To elaborate, barring any silly mathematical errors, there are only 3 possible answers commonly given, depending on your level of Chemistry conceptual understanding : the U grade answer, the D grade answer, and the A grade answer. Based on your answer, I'll assign you your grade.

      Edited by UltimaOnline 08 Jul `17, 5:23PM
    • ...take on the Singapore Education System, and on being a student in Raffles Junior College. It's a pity the video has since been taken ... time to hear my story. I was from Victoria School (VS) and Raffles Junior College (RJC). Growing up, I was taught to work ...

      Edited by UltimaOnline 06 Jul `17, 11:12PM
    • If you (as a JC student) found RJC Kevin Wee's personal story inspiring or at least helpful to you in some way, you might also be interested in hearing HCJC Xin Lin's story as well. She too, was stressed out by the life as a student in an elite JC, but in case you're wondering, she didn't burn her A level certificate.

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      Truth behind my JC life :

      https://stopthe-pretence.blogspot.sg/2012/03/truth-behind-my-jc-life.html

    • On a UK student forum, a girl posted the following :

      Okay a bit of background about me - I'm very ambitious and I always have been very academic, I like being successful and academia is my passion. I am studying for my masters degree in a science subject, and I might pursue a PhD. I have all of these big dreams for the future that I'm working on slowly. I've always wanted a partner who is similar to me somewhat so he has a similar passion for academia, or at least is working towards his dream job and has big goals.

      My current boyfriend lives in another country at the moment. When I met him he was exactly what I wanted, he had these big dreams and was studying so hard everyday because he was so determined, he wanted to be a doctor and was aiming for medical school, I loved that. Anyway, he said he didn't get the grades he wanted to and would rather not go to any med school at all than a 'crap one', and now doesn't want to become a doctor and isn't going to university. He's happy working in his father's clothing boutique. He says if he moves to England and marries me, he's happy opening up a little clothes shop and selling clothes. This shocks me because he's always talked about his extreme passion to become a doctor so this is such a change. Plus in terms of job prospects, if he comes to England, he has no degree, no A levels or GCSE's, just an international high school qualification.

      I feel guilty for feeling very disappointed in him, he could've retaken this exam, he could go to this 'crap' med school and succeed and STILL become a doctor but he's given up. Love shouldn't be about dreams/goals but I feel like we are becoming so incompatible and I should lower my standards but I feel like we are so different now. Someone please knock some sense into me.

      Someone then replied her :

      It's this attitude of partners judging others capabilities which leads to insecurities and low self-esteem. If you love him, you'll accept him for whatever he does.

      My personal comments :

      True love is indeed unconditional, but loving someone unconditionally doesn't necessarily mean he/she is the right person for you to marry. For a marriage to work, you'll need a lot more than unconditional love. You need mutually beneficial and complementary characters, personalities, habits, philosophies and goals (on every level, from professional career to family & friends to spirituality), and you'll need financial stability and sufficiency as well. Too many marriages break down and end in divorce, just because one or both spouse(s) kena financial difficulty, even if they (at initial point of marriage) truly and deeply loved each other.

    • Only 2 more weeks before the Special (Permanent) Discount Offer for JC2 students expires. I won't be offering any more such discount offers after July.

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    • Although the new H2 Chemistry syllabus specifies only a qualitative treatment of the Nernst equation is required, but you can bet your ass that most JCs will set Prelim paper questions on a quantitative treatment of the Nernst equation, and so will Cambridge, afterall what better way to illustrate a qualitative understanding than to perform calculations quantitatively?

      I have an extensive collection of Nernst equation problems ready for my BedokFunland JC students. All other students can go ask their school teacher or private tutor for practice on Nernst equation problems, and/or go Google out such Nernst equation problems on the internet for yourself to practice on. Have fun! :)

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      https://en.wikipedia.org/wiki/Nernst_equation

      Edited by UltimaOnline 10 Jul `17, 11:14PM
    • A BedokFunland JC Original H2 Chemistry Challenge

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    • [H2 Chemistry] - "Why or how do acid attacks cause disfigurement?"

      Such a simple Chemistry question with such an obvious answer, but you'll be surprised most JC students don't know the answer. And if you protest, "But acid attacks are not in the H2 syllabus!", my retort is : if you've truly educated yourself in Chemistry, it means to intelligently apply whatever you've learnt within the syllabus, to novel contexts beyond the syllabus. So yeah, certainly expect to have Cambridge do this for Chemistry as well, coz it would be totally unfair and a bloody shame if H2 Chemistry and/or H2 Physics loses to H2 Biology in this didactic, pedagogical, examinational characteristic :

      There will be one or more stimulus materials which may be taken or adapted from a source such as a scientific journal or book which may not necessarily relate directly to the content of the syllabus. Questions may require candidates to explain terms used in the passage, analyse data, justify decisions, perform calculations and draw conclusions based on information in the stimulus material.

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      Acid attack first aid: What you need to do immediately to help victims

      https://sg.yahoo.com/news/acid-attack-first-aid-immediately-131700262.html

      Edited by UltimaOnline 15 Jul `17, 5:21AM
    • Last 2 weeks before my Special Permanent Discount offer for 2017 JC2 students expire, and this Special Permanent Discount will no longer be offered after July 2017.

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    • To prevent your child growing up with a life-long (and potentially fatal) allergy of tree nuts and peanuts, there is increasing evidence that exposing your young toddler to small amounts of tree nuts and peanuts at a very young age, can help to prevent your child from developing an allergy to tree nuts and peanuts as he/she grows older, machiam vaccinating him to confer immunity. Note that tree nut allergy is a distinct and separate allergy from peanut allergy, and small amounts of both types of nuts should be given to young toddlers at a very young age.

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      http://mothership.sg/2017/07/child-had-severe-peanut-allergic-reaction-on-sia-flight-when-too-many-people-opened-bags-of-peanuts/

      Edited by UltimaOnline 18 Jul `17, 11:10PM
    • [Medical] - Startup touts neuro-electrostimulation device as 'medicine for the brain'

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      https://sg.yahoo.com/news/startup-touts-neuro-stimulation-medicine-brain-182659448.html

    • Last week of July left before my Special Discount Offer for 2017 JC2 students expires!

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      Watch the following video first, then answer my questions below :

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      https://www.youtube.com/watch?v=ShwH-B9FKNQ

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    • Originally posted by supercat:

      Hi there, I'm revising my A level chem + learning higher level chem to prepare for a chem test so I can exempt from chem mods. I have this question to ask.

      Which of the following compounds would react most rapidly with NaCN?
       
      a. 1-bromobutane
      b. (R)-2-bromobutane
      c. (S)-2-bromobutane
      d. 1-bromo-2-methylpropane

      My deduction is that either a or d is the answer, since b and c are technically the same compound (except the direction)

      Now, how do I know which will react faster? a has 1 R group, compared to d which has 2 R groups. I feel that d is more stable and so d would react most rapidly with NaCN. Am I right?

       


      This is still considered an A level Chem qn, so I'll help you out here. Once you do Uni level Chem proper, you can post your Uni Chem qns at The Chemical Forums, as my professional interest (as Mr BedokFunland JC) is specifically targeted at A level Chem only.

      Options A and D are both primary alkyl halides (your thinking that Option D is a secondary alkyl halide is incorrect : only if Option D was 2-bromo-2-methylpropane, then it would be tertiary, and 1-bromo-2-methylpropane is still primary), hence the electronics factor is similar. Therefore, the least sterically hindered Option A would be the fastest.

      For Options B and C, apart from your correct deduction that optical isomerism is irrelevant to the rate of reaction, let's consider them for the sake of comparison with Options A & D. Even though electronics would favor the secondary alkyl halides Options B & C for SN1 (over primary alkyl halide Options A & D), but the strong NC- nucleophile would favor SN2 anyway. Hence being SN2, Option A is fastest, followed by Option D, with Options B and C the slowest.

      If instead of 1-bromo-2-methylpropane, 2-bromo-2-methylpropane was specified for Option D (which was what you were prolly thinking of), then Option D (tertiary) would be faster than B & C (secondary) only if SN1 was favored (ie. weak nucleophile, and preferably protic solvent). Since SN2 is favored (ie. strong nucleophile, preferably aprotic solvent) in this question (although the solvent isn't specified by the question), then if Option D was 2-bromo-2-methylpropane, Option A (primary) would still be the fastest (even moreso than Option D being 1-bromo-2-methylpropane), followed by Options B & C, with Option D the slowest (due to greatest steric hindrance).

      Note that we've only considered nucleophilic aliphatic substitution SN1 and SN2 here, rather than elimination E1 and E2 (since solvent and temperature weren't specified by the question). If E1 and E2 are to be considered, a primary alkyl halide in an aprotic solvent with a strong Bronsted-Lowry base such as the NC- anion would favor E2 over E1, while a tertiary alkyl halide in a protic solvent with a weak Bronsted-Lowry base would favor E1 over E2.

      Edited by UltimaOnline 23 Jul `17, 9:53PM
    • Last few days before my Special Discount Offer for 2017 JC2 students expires, and won't be offered again for the rest of 2017!

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      There are over 200+ visitors to this H2 Chemistry thread every day, and yet almost all are silent lurkers. I know some of you lurkers are Singapore private tutors and Singapore school JC teachers, as well as foreign overseas visitors (students + teachers + tutors). But some of you are Singapore JC students, so to these students, why don't you make use of SgForums to register an account, and post your H2 Chem questions here? It's free to ask for help here, might as well make use of it. (Students who already have their own private tutors should ask your private tutors directly, eg. via WhatsAapp.)

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      So it wasn't the lychee fruit per se that caused the acute encephalitis deaths afterall, but the insecticide used.

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      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 :

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      Endosulfan is a derivative of hexachlorocyclopentadiene, and is produced by the Diels-Alder reaction of hexachlorocyclopentadiene with cis-butene-1,4-diol and subsequent reaction of the adduct with thionyl chloride.

      Q1. Draw the full electron-flow curved-arrow reaction mechanism for every step of the synthesis pathway :

      Cyclopentadiene -----> Octachlorocyclopentane -----> Hexachlorocyclopentadiene -----> Endosulfan alcohol -----> Endosulfan

      Technical endosulfan is a 7:3 mixture of stereoisomers, designated α and β. α- and β-Endosulfan are configurational isomers arising from the pyramidal stereochemistry of the teravalent sulfur. α-Endosulfan is the more thermodynamically stable of the two, and β-Endosulfan irreversibly converts to the α isomer, although the conversion is slow.

      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.

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      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.

      Edited by UltimaOnline 26 Jul `17, 6:39AM
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