2016 A Level H2 Chemistry Paper 2, 3, 1 discussions

last SG · 2016-11-08T20:10:45+00:00

I would think they should accept only NO2+S02=SO3+NO then regeneration bla bla blaso its like a homogeneous catalyst and Oxidising agent i would think elect...

UltimaOnline SG

Updated after Paper 1 :

kyungsoostan and Sir3,

A grade boundary for this year will most likely be approximately 75% (overall, combining all papers including SPA), depending on the entire cohort's performance.

However, note that your own (ie. all students') estimation of your marks may be inaccurate (eg. you don't actually know your SPA marks, you may have made careless mistakes you didn't realize, Cambridge's required answer may be different from your school's taught answer, etc).

Notwithstanding, assuming your estimation is accurate, then kyungsoostan's 77% is a safe A grade, and Sir3's 73.5% is a possible A grade. As long as you get > 70%, it's always *possible* to get an A grade (just that your chances increase dramatically at 75%), because the cohort's performance also has to be taken into account.

Guys I'm really trembling in fear... First i screw up paper2 (actually all my friends said it was hard) so i think i score around low B for that paper itself. Than for Paper 3, it was so easy! , but fml yeah i screw it up and my whole organic part was blank and i mixed up my R&C and haix. So my paper 3 was about low B too. yeah although i screw up, low B was quite possible. So based off p2 and p3 i got around 60-64%. Today's paper 2, i scored 27/40. First page all wrong idk what was i even thinking if not couldve 31 sia. but yeah its over. With those 3 papers i think i should be around 65 % AT MOST. Lets say spa affects my grades a little, will i drop to a D? I really do not want a H2 D... Haix. my uni course is AAB sia but i might end up with AAD if my chem really xiao suay.

Prepare for the worst, hope for the best. From your description, your most likely grade is a C, with a small chance of B or D.

Accordingly, be psychologically prepared to choose backup Uni courses with lower UAS requirements, and/or retake A levels as a private candidate (though if you have NS obligations, you've to decide exactly when to retake your A levels).

http://www.nus.edu.sg/oam/gradeprofile/sprogramme-igp.html

http://www3.ntu.edu.sg/oad2/website_files/IGP/NTU_IGP.pdf

This may sound harsh, but it isn't meant to demoralize you (of course you would rather hear soothing assurances like "no worries, you'll probably still get your B grade" but that's mere consolation not honest clarification), but rather to remind you, that whatever happens, make the most of it. Use every opportunity in life to grow, including growing in fortitude and resilience. Doing badly for A levels isn't the end, there are always 2nd chances in life, but only if you're willing to give them to yourself.

__________________________

Updated the night after P3

Anyway (not that anyone cares), but in case someone is wondering why I felt Q1 was time-consuming, it's because, while the question didn't actually ask for it (in fact only rather simple questions were asked about it), for the sake of understanding, I took my time to figure out the full mechanisms behind the Monsanto process, which are rather interesting, and the Monsanto process actually has much potential for many more challenging questions to be asked on it. Rather wasted, that Cambridge only asked very simple questions on the Monsanto process.

Since nobody else did what I did, then Q1 wouldn't be considered time-consuming. In which case since only Q3 is considered time-consuming (everyone agrees), I guess this Paper 3 should be considered a standard paper in terms of difficulty (though I still felt P2 was even easier than P3, prolly coz I love to write too much for open ended P3 qns every year which is consequently time consuming, but apparently I'm the only one, everyone else thinks P2 is tougher than P3), so I'm gonna re-adjust the expected grade boundary back to 75% (again, I stress this is of course an unofficial % expectation, because the performance of the entire Sg cohort also needs to be taken into consideration, and MOE-SEAB will never release the actual A grade boundary for each year).

Edited to add : in case anyone is looking for full solutions, I won't be providing them here ; many Singapore JCs' Chem departments will be preparing the solutions, as well as several private tutors and tuition centers, who will probably upload their solutions in pdf format on their tuition websites or google drive or scribd, etc. You can look for the solutions online yourself, or ask your school teachers if your school's Chem dept will be providing the full answers.

Updated right after P3

How did you JC students (and tutor/teachers such as TheFire521) find the Paper 3 today? How did your schoolmates find the Paper 3? Which Qn did you not do?

I estimate it's slightly on the tough side, due to Q1 and Q3 out of the 5 Qns being slightly time consuming.

Overall, A grade boundary may be approx (updated back to) 75% (based solely on difficulty of Papers 2 + 3, not yet considering performance of Singapore cohort, which I would not know).

Edited after P2 to add : As to the concerns raised by alliance88 and houdini_00, I never claimed to be (in fact, I can assure you I'm *not*) speaking on behalf of Cambridge or MOE-SEAB regarding official grade boundaries. Afterall, the bell-curve is subject to the performance of the entire Singapore JC cohort, which I've no way of knowing. I'm only giving my opinion (for whatever it's worth) based on the relative difficulty of the paper, without considering the performance of the entire Singapore JC cohort.

I simply assumed (mistakenly, perhaps) it would be understood by everyone reading this thread, that I was just giving my own opinion, whatever it's worth, (similarly to how Bilahari Kausikan is not, and never claimed to be, speaking on behalf of the PAP government whenever he writes an opinion article) on how the A grade boundary might be swayed by the difficulty of the Paper, just as how many other private tutors and JC teachers would also give their own opinion on this matter, after each paper.

You're (not just alliance88 and houdini_00, but everyone else as well who feels likewise) welcome to ignore my future opinion posts on possible shifts on the A grade boundary, eg. after the upcoming P3 and P1, if you feel they're not useful or worse, discouraging.

Edited after feedback from you students on this forum saying many students found today's Paper 2 on the tough side.

Overall, I'd say this was a rather standard Paper 2 in terms of difficulty.

Accordingly, as it stands (P2 alone), the A grade boundary will likely remain approximately 75% (as with most previous years).

Let's wait and see how goes P3 and P1, and adjust our A grade boundary expectations then.

To all JC2 students reading this : how did you and your schoolmates generally find today's paper? easy or tough?

Any questions and discussions regarding the Singapore A level 2016 H2 Chemistry Paper 2, 3 and 1, post here in this thread.

Thefire521 SG

Wa siao liao

This paper still okay somehow how come planning so easy now

But bio people the fatty acid dont read q also can do sia

UltimaOnline SG

Edited after feedback from you students on this forum saying many students found this paper on the tough side.

A standard Paper 2 in terms of difficulty.

Accordingly, as it stands (P2 alone), the A grade boundary will likely remain approximately 75% (as with most previous years).

Let's wait and see how goes P3 and P1, and adjust our A grade boundary expectations then.

theophilus SG

Watt ? easy, for A level standard I think quite challenging ah. Like a mid tier prelim standard I feel.

So anyone think they got the last part of question 1 right ? the one regarding leaving olive oil forming rancid solution or sth. I think i only got one mark by stating hydrolysis causing free fatty acids and glycerol. But I dont know the other reactions, like forming the di acid etc

Also quoting data from data booklet to show that K is more reactive than Cu, isit okay to quote the IE values and E values ???

DaLibrary SG

most of my peers found it quite challenging

for the last part of question 1, i think it's ester undergoing acidic hydrolysis to form free fatty acids and glycerol and also alkenes undergoing strong oxidation to form dicarboxylic acid and such.

i only quoted E values to explain why k is more reactive than cu so i'm not too sure about IE values

Tviq SG

??!!?! Easy? Definitely isn't easy compared to the previous years.Many of my schoolmates found it tough.Planning was quite simple, but the rest of the questions was more challenging. Almost similar prelims. And yes, i wasn't sure why k is more reactive than Cu

theophilus SG

I was thinking of oxidation too but there were insufficient reagents to cause that to happen. Like alcohol all need to kena pretty strong oxidizing agents and even if it did, glycerol was a tri hydroxy or 3 oh groups, how to form dicarboxyllic ?? Ohhh mannnnn

ScrewedUpO's SG

Thefire521 SG

@Ultima the bio students found it quite okay.

As for the 4 mark rancid question, its like an oxidative cleavage of the alkene in the long fatty acid to give the dicarboxylic acid and the short fatty acid chains.

As for the 1 mark last part significance question since u calculated no. Of double bond is 2.85, then u will just have to say what is the other component of the olive oil

As for comparing btw reactivitt of k and cu they did say from data booklet or otherwise so i would think either e value of ionisation energy or if u talk about periodic trends nuclear energy increase bla bla bla they shd accept

Tho i have to say they r moving to more application based q and paper 3 will spam all those inorgs and org deductions

UltimaOnline SG

After feedback from you students on this forum saying many students found this paper on the tough side, I've revised my judgment to say today's Paper 2 was a rather standard Paper in terms of difficulty.

Accordingly, as it stands (P2 alone), the A grade boundary will likely remain approximately 75% (as with most previous years).

Regarding the olive oil oxidative rancidity question.

The C=C group undergoes oxidative cleavage.

The following was not asked in the question and is hence not required. Just fyi.

This is known as oxidative rancidity of unsaturated fatty acids, which involves a free radical mechanism (the free radical character being delocalized hence stabilized by resonance over the C=C groups), either initiated by UV / sunlight (photo-oxidation), or catalyzed by a bacteria enzyme or transition metal.

Skyrev SG

Hi Ultima, do you know the average percentage for a B grade based on previous years?

UltimaOnline SG

Hi Ultima, do you know the average percentage for a B grade based on previous years?

B grades and below usually remain mostly unchanged (or less deviation) from the standard grade boundaries, compared to A grade boundary.

Unless P3 + P1 are surprisingly tough, B grade boundary should remain as just slightly above 60%.

Pjc rocks SG

To explain why copper is more reactive than potassium, I used the E null value to obtain . The E null value is more negative for K which means that it is readily oxidised to give K +. Is this explanation okay? Quite skeptical since it is 4 marks. Furthermore, for planning, how to determine that the reaction is complete.

grace98 SG

HI NEED HELP HERE. I was caught for not putting my pen down after the time and asked to write a misconduct report. What will happen to me?? Am I in big big trouble?

UltimaOnline SG

It's ok, but won't be sufficient to score all 4 marks (most students will only score 2 or 3 of the 4 marks). Just stating the ionization energy *and* redox potential, scores just 1 mark. The explanation (which I won't give here) is worth 3 marks.

Ensure the solid is completely dissolved, assisted by manually stirring with a glass rod.

UltimaOnline SG

HI NEED HELP HERE. I was caught for not putting my pen down after the time and asked to write a misconduct report. What will happen to me?? Am I in big big trouble?

Unlikely. You can always ask your own school teachers for their opinion on this (since they might have a better idea of your report), but most likely nothing will happen. Don't worry and focus well on preparing for the rest of your upcoming papers.

Skyrev SG

Ensure the solid is completely dissolved, assisted by manually stirring with a glass rod.

I left the conical flask of the mixture to stand in a water bath to ensure complete dissolving. Is that okay?

TheSpaceManatee SG

for the observation question in planning (2 marks) can i say effervescence and deep blue solid dissolves in excess h2so4 without saying a blue solution is formed?

For the K more reactive than copper question, I talked about much higher effective nuclear charge in Cu hence 4s1 electron more tightly bound to nucleus blah blah... correct?

for the draw nucleophillic addition mechanism, in the second step is it the lone pair on O just attack a H+ or is it lone pair attack H in H2O to give the product and OH-?

and for the NO2 effect on environment can just say photochemical smog and acid rain without talking about polluting river or corroding limestone buildings?

Also, for slow corrosion of coper i said that a layer of CuO forms that will slow down corrosion, is that correct?

other than that should be ok, but I skipped 10 marks of planning, is it still possible to get A? :( Thanks

theophilus SG

For the Cu and K explaination, does it run along the lines of activation energy for forming ionic compounds?

And there was a question about what does the c double bond do to the melting point, isit a super straighforward question and just state that it decreases the melting point or one step deeper some how having an alkene makes the melting point lower?

Thomas00 SG

I think the paper is quite tricky. The transition metal ligand question was quite tough. Didn't manage to draw the structure.

And can use pencil draw mechanism? Haha, scared they don't accept