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

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).

UltimaOnline SG

Hi, does anyone know the answer for 1 eiv? Is B an intermediate or a catalyst???

Catalyst.

UltimaOnline SG

Just curious does this 75 mark range include spa? If it includes spa then it would have been much more attainable, given that it is easy to score full marks or close to that in spa.

Overall.

I suspect many students may overestimate their SPA marks.

Thomas00 SG

Ultima, any rough idea about the range for B,C and D grade roughly? Which grade is usually the majority?

Thomas00 SG

So is it catayst, catalyst and reactant for A,B and C respectively?

UltimaOnline SG

Ultima, any rough idea about the range for B,C and D grade roughly? Which grade is usually the majority?

The bell-curve and concordant grade boundaries are relative and varying, not absolute, so every year, a different % of students will score A grade, B grade, etc.

If it were absolute (which it's not), then every grade should have equal % of students.

In practice, B grades are usually the 'majority', for most years, relative to all the other grades.

The grade boundaries for C and D do not differ significantly from the basic grade boundary used in Singapore JCs, for most years. B grade is usually a couple of % points above 60% for H2 Chem, depending on difficulty of papers and entire cohort's performance.

UltimaOnline SG

So is it catayst, catalyst and reactant for A,B and C respectively?

Yes.

Thefire521 SG

Mine was 0.000400atm^-2

seems like a correct kp though dont remember the next 2 digits after 4

Thefire521 SG

Ultima, any rough idea about the range for B,C and D grade roughly? Which grade is usually the majority?

Though i have to say every year consistently there would be 60-70% of students in top JC's getting their As for chemistry, physics, biology and 80% for Mathematics, considering there are almost around 800-1000 students per sch, i would say a sizeable number would get their As

dont worry too much. the A depends on many factors, and largely also luck. so i think try your best and see what you get and move on in life

Thomas00 SG

Thanks Ultima and Fire for responses! I'm not from the top few JCs so i am just trying my best and see how things goes. Would be hoping for B and Cs.

Acerbicia SG

Haha, I actually thought that this paper was pretty easy (slightly easier than usual As? and a LOT easier than schools' prelims). Not much application/new stuff (like grignard, williamson's, thiols etc) except for Q1, mostly calculations or organic. Surprised kinetics and Ksp didn't come out at all.

Finished it within 1.5hrs or so. I did Q2-5 and actually spent the least time on Q3 haha like 15 minutes although afterwards I was afraid they'd mark for deductions so I went back to painstakenly write them out LOL. Stuff I lost marks at were things I forgot or didn't study (e.g. principles of VSEPR) or couldn't explain well. Carelessness was definitely a factor too.

I messed up my energy cycle LOL drew my arrow the wrong way but funnily enough I modded it to get a positive value because I know it's not supposed to be negative haha though for some reason it didn't occur to me that the arrow should have been in the other direction. I did get 202. Hopefully the marker is half-asleep and doesn't realize. Heh.

That reminds me- Ultima/Fire/any peers: I explained that the C-H bond is very strong to explain that alkanes are unreactive but ignored the C-C bond as it's weaker and not characteristic of alkanes. Is that fine?

P.S. If anyone's scared that I found it easy- I think I'm pretty solid when it comes to calculations/elucidation/synthesis etc so I'm good with P3 where I get to choose questions with minimal explanation. I suck at explaining (my P2 was... well HAHA not good, not good, not good at all). I definitely lost more marks in P2 than in P3 LOL.

UltimaOnline SG

15min for Q3, you might hold the Singapore record for fastest completion time for Q3 (but your answers must be all correct of course). Well done.

Cambridge will accept any 2 valid reasons for the inertness of alkanes. If you intend to use bond strength as a reason, then you need to include both C-C and C-H bonds for 1 mark.

Sir3 SG

Hi for qn 1 for ABC

If i wrote A was a base(HI) cause it donated proton in the first step and C was a ligand instead of a reactant would i be marked wrong?? I didnt see the preamble where they said that A B C must be a catalyst,reactant or intermediate

UltimaOnline SG

Hi for qn 1 for ABC

Zero marks for your A and C. For Cambridge, that's the justified penalty for not reading and following the question's instructions.

zenthyl SG

Thanks for the replies.

I pretty much had a good time doing this paper - and most of my answers were correct after cross-checking with my peers actually.

I'm just worried for the questions with high explaination mark weightage (like the ones with difference in b.p. are 6 marks) bc they'll probably want to see certain key words. So idk thankfully I did know how to answer but on the flipside I took a little more time to explain carefully (for the fear of losing marks haha).

I took around 1 hour 30 mins to complete it too? Did Q1,2,4,5 tho. Anyway I hope it was as good for other people as it was for me :) And yeah I did screw up paper 2. Maybe.

Thefire521 SG

Thanks for the replies.

I pretty much had a good time doing this paper - and most of my answers were correct after cross-checking with my peers actually.

I took around 1 hour 30 mins to complete it too? Did Q1,2,4,5 tho. Anyway I hope it was as good for other people as it was for me :) And yeah I did screw up paper 2. Maybe.

Yes, which is why if you had studied and memorised the learning outcomes one by one, the explanation for the reactivity questions, vsepr, acidity would not have been an issue, though they are probably more lenient than schools LOL (if you have seen CIE mark schemes before)

Some examiners also hate looking at rambling things they rather you explain it consisely, but then again better to be safe than sorry

Did you spend the last 30 minutes trying Q3? Haha

Who knows? Paper 1 might be a killer!

Sir3 SG

Hi for why alkanes are inert, if i gave 2 reasons which are 1.the c-h bond is stronf thus lots of energy needed and 2. I said that electronegativity between carbon and hydrogen is similiar so carbon will not acquire a partial positive charge will this get 2 marks? (On a side note one of my classmataes stated that carbon is unable to expand its octet structure in alkanes ao it is unreactive..will that get the mark?it sounds unusual though)

As for the bond energy qn, if i drew my diagram correctly but i forgot to times 2 the bond formation of brf3, how many marks are lost?

And for drawing fo electrochem cell, i didnt state that it needs to be under 298k and 1atm, but i did label 1 mol/dm^3 of ions so how many marks are lost for this qn?

thanks.. Worried here đ

Skyrev SG

Shouldn't the standard enthalpy change of formation of BrF3(l) be -150.5 kJmol^-1?

Thefire521 SG

Shouldn't the standard enthalpy change of formation of BrF3(l) be -150.5 kJmol^-1?

dont think so. I think they gave it as -300 something? no? dont have the paper with me now

Thefire521 SG

As for the bond energy qn, if i drew my diagram correctly but i forgot to times 2 the bond formation of brf3, how many marks are lost?

And for drawing fo electrochem cell, i didnt state that it needs to be under 298k and 1atm, but i did label 1 mol/dm^3 of ions so how many marks are lost for this qn?

thanks.. Worried here 

Hi. Saying alkanes are inert because c-h bond is strong is not a valid reason. Alkenes, for example have c=c bonds which are even stronger (in terms of bond energy), but they are more reactive.

I would more or less think there are many many ways to justify, whether is it by polarity or the fact that they have no lone pair of electrons available for donation (so rarely becomes nucleophile nor electron deficient to become electrophile...)

If you say carbon cannot expand octet, i would think they might give it to you but to think of it the same reasoning-that alkenes are also made up of carbons which cannot expand their octet, so this reason isnt very important.. (i believe students probably give this answer alot when asked why ccl4 cannot hydrolyse in water, but should not for this question)

If you did not label full set of standard conditions, then that should be 1 mark gone.

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