2015 A Level H2 Chemistry Paper 1, 2, 3

last SG · 2015-11-06T20:43:51+00:00

History students!! Do check out my site for notes that will guarantee you an A in H2 History :) pass on the message to all who are struggling with this subje...

Weihaw08 SG

Indeed this is a tricky question, and many students struggled with this. Because in the H2 syllabus, every sigma bond is formed by the head-on or end-on overlap of either s orbitals or hybridized (sp, sp2, sp3) orbitals. But going beyond the H2 syllabus, sigma bonds can indeed be formed by the head-on or end-on overlap of p orbitals as well. Chemistry is chemistry (regardless of in or out of syllabus), so the correct answer to this question is still "sigma bonds can be formed by either s or p orbitals".

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

https://sites.google.com/site/ed350201003/Task

But, the question specifically refer to hydrocarbons only. :0

julians199 SG

Vitalitylx SG

40 is B because 3 has a plane of symmetry. Take a look at the 3d shape , plane 3 is exactly a mirror image whereas 1 is not.

studentxyz SG

UltimaOnline SG

In this case the context is hydrocarbon..so im guess now the s orbital of hydrogen overlap with (unhybridised) p orbital of C to form a C-H bond?

-_-" I completely missed the word "hydrocarbons". In this context then, you're right, D appears to be a better answer than B. The C-H bond in hydrocarbons are always formed by the head-on or end-on overlap between the s orbital of the H atom and the sp or sp2 or sp3 hybridized orbital of the C atom.

Tricky dicky Cambridge. -_-"

LemonRay SG

Ahhh careless, careless and more careless mistakes. 33/40 :(

studentxyz SG

hi, just curious, but how do you estimate that you need 75% to get an A? because i keep hearing people say that you need more than 80% :(

UltimaOnline SG

hi, just curious, but how do you estimate that you need 75% to get an A? because i keep hearing people say that you need more than 80% :(

Ok here's the thing : the way most students count their marks, assuming Cambridge will accept all their answers (eg. just because their school teachers or private tutors taught them to write that way), then you should play safe and go ahead and consider 80% to be the A grade boundary. But if you count your marks strictly (and err on the side of caution, ie. assume you didn't get that particular mark if you're not sure it's 100% acceptable by Cambridge), then following the Cambridge Mark Scheme (which I know) and the process of Cambridge computation of grade boundaries based on the bell-curve (which I know), then overall score > 75% is safe. I can't reveal any more details than this.

studentxyz SG

does the 70-75 mark range apply to other subjects like math? or is it just the traditional boundary for chem?

UltimaOnline SG

does the 70-75 mark range apply to other subjects like math? or is it just the traditional boundary for chem?

Only applies to H2 Chemistry. Different subjects have different grade boundaries and bell-curves.

Mankey123 SG

Why isn't Q14 A?

AlexSummers SG

for Q21, isnt it 4 isomers (C)? pent-1-yne, pent-2-yne, pent-3-yne and 3-methylbut-1-yne?

Vitalitylx SG

for qn 2, what about C-C bond forming head on with p-orbital since its hybridised?

UltimaOnline SG

Why isn't Q14 A?

A would be right if NO2 is 1st order, but it's 2nd order.

UltimaOnline SG

for Q21, isnt it 4 isomers (C)? pent-1-yne, pent-2-yne, pent-3-yne and 3-methylbut-1-yne?

pent-2-yne = pent-3-yne

UltimaOnline SG

for qn 2, what about C-C bond forming head on with p-orbital since its hybridised?

C-C sigma bonds are either sp-sp, sp-sp2, sp-sp3, sp2-sp, sp3-sp, sp2-sp2, sp3-sp2, sp2-sp3, or sp3-sp3.

If you interpret the question to include p orbitals as part of hybridized orbitals, then yes, B would be the answer. If you interpret it to mean unhybridized orbitals only, then D would be the answer. In the context of hydrocarbons at least.

UltimaOnline SG

Wynrox posted : "Unfortunately for me you are right for qn40... đ For qn 31 I was taught by my school that any ion with configuration 4s0 3d6 will become 4s1 3d5. Not sure which is correct though."

Yes totally unfortunately for you, but it's not surprising at all that I'm right.

That's true only for atoms in their ground states, not ions.

You can be sure I'm correct, though.

Fe2+ is [Ar] 4s0 3d6

Trust BedokFunland JC > Singapore JCs, ftw.

Vitalitylx SG

Oh, so in this case question 2 is interpreted to only talk about unhybridized orbitals? Hence D is the answer?

UltimaOnline SG

Oh, so in this case question 2 is interpreted to only talk about unhybridized orbitals? Hence D is the answer?

Cambridge's fault for being ambiguous. Singapore JC school teachers and other private tutors are divided on what's the best answer.

Ibenedictkoh SG

In this case, for q2 will they accept B or D? Coz I know there's a question which accepts 2 answers for last year p1.

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