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2017 H2 Chemistry JC1 & 2 students post your questions here

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  • MapPwner's Avatar
    138 posts since Aug '15
    • Originally posted by Ellipsisss:

       

      Haha slightly comforting, just hope I don't get trample on even in bell curve :/

       

      Oh MapPwner congrats on your reddit comment becoming famous xD

      I was bored merely and just commented there+posted suggested answers for the practical(which aren't 100% accurate and shouldn't be taken to be fully correct,especially QA explanations)

      But of course,there are slight disagreements to the answers i posted,such as the question in the practical showing the reaction mechanism of Fe(H2O)6 3+ catalyst with H2O2 to decompose it,which the question required with your observations.My suggested answer just said stating the formation of an intermediate complex in step 1 as the catalyst is used up,and regeneration of the catalyst in step 3 is already 2 marks secured,and of course someone said must use observations throughout haha,which i think should be the last mark bah to get the full 3 marks for the question.Maybe you can suggest what u wrote for this question?

    • Originally posted by UltimaOnline:

      Alongside RJC and DHS, this year's VJC prelim papers also rank amongst the top of all Singapore JCs' prelim papers, in terms of quality of questions and standard of difficulty.

      Based on yesterday's P4, you can expect that this year's 2017 A level's P2, P3 and P1 to be comparable with the RJC, DHS and VJC papers. So be sure you (ie. all JC students intent of scoring a distinction for your H2 Chem) go through these 3 JCs' 2017 prelim papers very thoroughly.

      Disclaimer : I haven't, and probably won't, go through all of the other remaining Singapore JCs' 2017 prelim papers (I've gone through about 2/3 of all JCs, and find the quality of the RJC, DHS and VJC 2017 prelim papers in particular to be worthy of honorable mention). So it's entirely possible that some other JCs' 2017 prelim papers are every bit as good as RJC / DHS / VJC. And everyone is entitled to his/her own opinion. If you've any specific JC's 2017 prelim papers that you particularly enjoyed doing (helps if you're masochistic), do share your vote here.

      Overall, I'm honestly glad to see a substantial increase in both the quality and difficulty of all JCs prelim papers this year. Very good work done here setting the 2017 prelim papers, all Singapore JC teachers. And based on yesterday's P4, Cambridge certainly seems to have the same idea (ie. raising the quality, creativity and difficulty of the A level papers for the new syllabus). So be mentally (and emotionally!) well-prepared.

      Thanks for the tip UltimaOnline,will definitely try out RJC/VJC/DHS papers when I'm free.

      Completed DHS P2 so far and relatively minimal mistakes made except for the sulfonic acids question,rest were relatively easy for me.

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    13,909 posts since May '05
    • Ellipsisss, no worries about my BedokFunland JC Challenge Qns. If Cambridge used my BedokFunland JC Challenge questions for A levels , the number of distinctions in the Singapore cohort would be reduced to 1%.

      Focus on doing as many 2017 Prelim Papers as you can now, both Ellipsisss and MapPwner (and all other students reading this thread). Any questions from any 2017 Prelim Papers, feel free to post here, I'll help you guys out.

      MapPwner and Ellipsisss, let us know which JC's 2017 Prelim Paper you vote to be the toughest. And individual questions as well, eg. MapPwner found the DHS question on sulfonation to be tough.

      In this way, the many silent JC student lurkers reading this thread can choose to attempt your recommended tough questions from 2017 Prelim Papers, and they can learn and benefit from such questions.

  • Hello199999's Avatar
    1 post since Oct '17
    • How do you rate SRJC chemistry prelim? When I was doing it, it seemed easy but in reality it wasn’t? Is the paper difficult? Or is it just that I’m not up to the mark?

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    13,909 posts since May '05
    • Originally posted by Hello199999:

      How do you rate SRJC chemistry prelim? When I was doing it, it seemed easy but in reality it wasn’t? Is the paper difficult? Or is it just that I’m not up to the mark?


      The SRJC 2017 Prelim Papers are very good, well-balanced papers, with a good spread of both easy and difficult questions. If this year's P4 is an accurate indicator of the difficulty level of the remaining papers, then you can expect the difficulty of this year's A level P1, P2 and P3 to be very close to the SRJC 2017 Prelim Papers. Of course, the remaining A level papers *could* be shockingly tougher or easier than everyone's expectations, but I seriously doubt the variance will be that large, most likely will be very close to this year's SRJC standard, which is already considered tougher than previous years' A level papers. Welcome to the new H2 syllabus.

      Good recommendation by Hello199999. All JC students do attempt the SRJC 2017 Prelim Papers.

      Any specific questions from any 2017 Prelim Paper, eg. SRJC, RJC, VJC, DHS, etc, that any student has query on, feel free to post here to ask for help.

  • MapPwner's Avatar
    138 posts since Aug '15
    • Originally posted by UltimaOnline:


      The SRJC 2017 Prelim Papers are very good, well-balanced papers, with a good spread of both easy and difficult questions. If this year's P4 is an accurate indicator of the difficulty level of the remaining papers, then you can expect the difficulty of this year's A level P1, P2 and P3 to be very close to the SRJC 2017 Prelim Papers. Of course, the remaining A level papers *could* be shockingly tougher or easier than everyone's expectations, but I seriously doubt the variance will be that large, most likely will be very close to this year's SRJC standard, which is already considered tougher than previous years' A level papers. Welcome to the new H2 syllabus.

      Good recommendation by Hello199999. All JC students do attempt the SRJC 2017 Prelim Papers.

      Any specific questions from any 2017 Prelim Paper, eg. SRJC, RJC, VJC, DHS, etc, that any student has query on, feel free to post here to ask for help.

      Just curious,how do you rate the difficulty of PJC and AJC chemistry prelim papers?I feel that AJ prelim is slightly harder but otherwise,more or less relatively manageable and very doable papers.

      I recently completed DHS P3,VJC P2,RJC P2.Personally felt that DHS P3 was relatively tricky.

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    13,909 posts since May '05
    • Originally posted by MapPwner:

      Just curious,how do you rate the difficulty of PJC and AJC chemistry prelim papers?I feel that AJ prelim is slightly harder but otherwise,more or less relatively manageable and very doable papers.

      I recently completed DHS P3,VJC P2,RJC P2.Personally felt that DHS P3 was relatively tricky.


      Both sets of the PJC and AJC 2017 papers are well-balanced papers (with a good spread of easy and slightly tough questions), that all JC students should certainly practice on.

      Difficulty-wise, as you say, AJC is slightly tougher (particularly P3) than PJC, and both JCs' 2017 papers are somewhat easier than the RJC / VJC / DHS / SRJC 2017 papers.

      It's fair to expect the difficulty standard of this year's A level exam papers to mostly lie somewhere in between the 2 difficulty levels, but of course, there's a small chance it could be an unexpected outlier : even easier than the PJC papers, or even tougher than the RJC papers, but this is extremely unlikely (based on the P4 just over, P2+3+1 are unlikely to be easy papers).

  • CKTR's Avatar
    84 posts since Jun '15
    • Hi UltimaOnline, for qns 10 VJC 2014 P3 qns 1a iii, why is it that the ratio of [Mg2+]/[Cu2+] = Kc?

       

      Edited by CKTR 02 Nov `17, 12:02AM
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    13,909 posts since May '05
    • Originally posted by CKTR:

      Hi UltimaOnline, for qns 10 VJC 2014 P3 qns 1a iii, why is it that the ratio of [Mg2+]/[Cu2+] = Kc?

       


      Because the equation is Cu2+(aq) + Mg(s) --> Cu(s) + Mg2+(aq), and the thermodynamic activity of solids is taken to be 1 (mathematical derivation of this is done at University level).

  • CKTR's Avatar
    84 posts since Jun '15
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    13,909 posts since May '05
    • Originally posted by CKTR:

      Oh yeah I forgot thanks.

      Btw I found ACJC the most challenging imo


      Excellent recommendation by CKTR!

      The ACJC 2017 prelim papers certainlyy belong to the upper difficulty tier of 2017 prelim papers, together with RJC / VJC / DHS / SRJC etc.

      Indeed in some ways, this might be just be my favorite set of 2017 prelim papers, due to it's multiple extensive questioning (ie. 5 questions across P2 & P3) of unfamiliar (ie. not taught within the H2 syllabus) curved-arrow electron-flow reaction mechanisms, which as some of you might know, is in line with BedokFunland JC style (ie. I would be utterly delighted if the actual Singapore A Level exam papers used the ACJC 2017 prelim papers).

      So all JC2 students serious about scoring a distinction grade, be sure you thoroughly go through this upper-tier set of ACJC / RJC / VJC / DHS / SRJC papers before next week's P2 & P3. Any questions post em here.

  • arianivel's Avatar
    1 post since Nov '17
    • Hi

      How about NYJC’s prelim paper? Like what is the difficulty level according to you?

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    13,909 posts since May '05
    • Originally posted by arianivel:

      Hi

      How about NYJC’s prelim paper? Like what is the difficulty level according to you?


      Difficulty-wise, given the high standards of the NYJC papers in recent years, a little disappointing this year. Quality of the papers is still good (and still recommended for all students to practice on), but difficulty-wise, it's somewhere in between the 2 difficulty tiers for this year.

  • MapPwner's Avatar
    138 posts since Aug '15
    • Originally posted by UltimaOnline:


      Excellent recommendation by CKTR!

      The ACJC 2017 prelim papers certainlyy belong to the upper difficulty tier of 2017 prelim papers, together with RJC / VJC / DHS / SRJC etc.

      Indeed in some ways, this might be just be my favorite set of 2017 prelim papers, due to it's multiple extensive questioning (ie. 5 questions across P2 & P3) of unfamiliar (ie. not taught within the H2 syllabus) curved-arrow electron-flow reaction mechanisms, which as some of you might know, is in line with BedokFunland JC style (ie. I would be utterly delighted if the actual Singapore A Level exam papers used the ACJC 2017 prelim papers).

      So all JC2 students serious about scoring a distinction grade, be sure you thoroughly go through this upper-tier set of ACJC / RJC / VJC / DHS / SRJC papers before next week's P2 & P3. Any questions post em here.

      I feel ACJC P2 is rather doable but P3 otherwise there are certain parts(reactions of halogens with H2SO4,decomposition of Group II nitrates) which are technically not part of our syallabus but tested in the paper somewhat stumped me and I read about them slightly in depth to play safe,as my school didn't touch on those as its said to be out of syallabus.

  • do12453's Avatar
    13 posts since Nov '17
    • Hello, wat is the use for

      Sect 6 (proton shift values)

      And sect 7 (charaxteristic infrared spectrum)

      I notice it is in the data book but nv use before. Is it testable?

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    13,909 posts since May '05
    • Originally posted by do12453:

      Hello, wat is the use for

      Sect 6 (proton shift values)

      And sect 7 (charaxteristic infrared spectrum)

      I notice it is in the data book but nv use before. Is it testable?


      H3 syllabus.

  • MapPwner's Avatar
    138 posts since Aug '15
    • Can I just ask whether in the formation of a triiodide ion,I3^-1,from Iodine and an iodide ion,one of the I in I2 forms a dative bond with the I^-1 to form a linear molecular geometry I3- structure?

      Likewise for [I2Br]^-1,one of the I in I2 forms a dative bond to the more electronegative Br- to form [I2Br]^-1 with the same molecular geometry?

      Are we expected to know grp 12/17 reactions in the current new syallabus,for instance such as reaction of Br2 with concentrated H2SO4?

       

      Edited by MapPwner 04 Nov `17, 5:23PM
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    13,909 posts since May '05
    • Originally posted by MapPwner:

      Can I just ask whether in the formation of a triiodide ion,I3^-1,from Iodine and an iodide ion,one of the I in I2 forms a dative bond with the I^-1 to form a linear molecular geometry I3- structure?

      Likewise for [I2Br]^-1,one of the I in I2 forms a dative bond to the more electronegative Br- to form [I2Br]^-1 with the same molecular geometry?

      Are we expected to know grp 12/17 reactions in the current new syallabus,for instance such as reaction of Br2 with concentrated H2SO4?

       


      To be precise, "accepts... from", not "forms... with". But bear in mind I- is an anion, and the adduct is an anion, so for dot-and-cross diagrams (if required), while the dative bond should still be shown with a dot-dot or cross-cross, a hollow-dot (ie. electron accepted from the species which reduced 1/2 I2 to the I- reactant, presumed to be the counter-cation present throughout, eg. K+) must be clearly shown as part of a lone pair in both the I- reactant and I3- product.

      Yes, of course (isn't it obvious why the ionic geometry of the adduct is linear?), Cambridge can certainly ask you to draw out the full mechanism (in which case no 'dative' arrowhead bonds should be shown anywhere in the product, just a curved arrow from the I- or Br- nucleophile to the I2 electrophile, then all straight lines (ie. normal bonds) in the product, any 'dative' arrowhead bonds shown will be penalized), as this mechanism is already much easier than the other ones asked in 2017 ACJC Prelim papers.

      The conceptual basics (eg. trend of redox potentials), yes. The technical details (eg. memorization of equations), no. But distinction A grade students are indeed expected to be exposed beyond the syllabus, and/or are expected to be intelligent enough to figure out the reaction, equation and products (eg. using Data Booklet for hints) even without prior exposure. So yes, Cambridge can indeed ask on these not-in-syllabus reactions, although Cambridge would probably be a little kinder, and give slightly more hints than Singapore JC prelim papers.

      Edited by UltimaOnline 04 Nov `17, 7:24PM
    • MapPwner, do you want me to explain why I3- or BrI2- has linear ionic geometry? Is that the part you have difficulty with? Or has my previous reply addressed your queries?

    • Ellipsisss, here's a chance for your 'redemption' (you were game enough to attempt my earlier BedokFunland JC Challenge Qn, but as I said, I'll only reveal the answers for such Challenge Qns to my own BedokFunland JC students, so I left you hanging back there regarding the imidazole ring of histidine, well, here's a simpler question that has a higher probability of being asked by Cambridge for the new H2 syllabus).

      Since the new syllabus specimen paper asked for the hybridization of N atoms (where in the old syllabus, questions were restricted to C atoms), almost all the 2017 Singapore JC Prelim Papers started following suit. So here's a BedokFunland JC question for all of you.

      State *and* explain the hybridization of the N atom in the amide functional group.

      Note : At Uni levels, the actual hybridization will be x% this, y% that, z% something else, but at A levels, you're expected to identify the single 'major' hybridization that contributes most to the actual hybridization.

      I'll leave it to you guys (feel free to attempt and post what you would write as your answer if this question comes out in this coming week's P2 or P3) to discuss this very easy question, I'm sure you guys don't need me to spoonfeed you the answer, but try to resist googling out the answer before attempting it yourself, that's just lazy.

  • do12453's Avatar
    13 posts since Nov '17
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    13,909 posts since May '05
    • Originally posted by do12453:

      Is it sp2 because amides are trigonal planar electron geometry?


      You'll need to elaborate to get full marks. If you say sp2 because of trigonal planar electron geometry, then why trigonal planar electron geometry?

  • do12453's Avatar
    13 posts since Nov '17
    • Is it because the 3 bond pairs for trigonal planar must be in the same plane? Hence if sp3 it will be trigonal pyramidal (not planar), and if sp the 2 p orbitals are not same plane?

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    13,909 posts since May '05
    • Originally posted by do12453:

      Is it because the 3 bond pairs for trigonal planar must be in the same plane? Hence if sp3 it will be trigonal pyramidal (not planar), and if sp the 2 p orbitals are not same plane?


      You're still missing the mark (literally, hehe).

      Comparing the N atoms in both amines and amides, both have 1 lone pair + 3 bond pairs, so why are their hybridizations different?

      I've given out too many clues liao, I'll leave it for other students here (including you silent lurkers, post leh!) to attempt and post their answers. See what they say.

    • Last 24 hours left before Paper 2. Any final questions from the 2017 Prelim Papers or TYS, better faster ask now!

      After P2 is done tomorrow (and P3 on Fri), I'll leave it to you students (eg. MapPwner) to lead the discussions on the questions.

      If anyone wants my comments on any P2 or P3 questions, pls type out the qn from memory (for P2), or upload a photo of the qn (for P3).

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