Originally posted by UltimaOnline:
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
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.
Originally posted by nelexus: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?
Ahhh careless, careless and more careless mistakes. 33/40 :(
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% :(
Originally posted by studentxyz: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% :(
Originally posted by UltimaOnline:
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.
does the 70-75 mark range apply to other subjects like math? or is it just the traditional boundary for chem?
Originally posted by studentxyz:does the 70-75 mark range apply to other subjects like math? or is it just the traditional boundary for chem?
Why isn't Q14 A?
for Q21, isnt it 4 isomers (C)? pent-1-yne, pent-2-yne, pent-3-yne and 3-methylbut-1-yne?
for qn 2, what about C-C bond forming head on with p-orbital since its hybridised?
Originally posted by Mankey123:Why isn't Q14 A?
Originally posted by AlexSummers:for Q21, isnt it 4 isomers (C)? pent-1-yne, pent-2-yne, pent-3-yne and 3-methylbut-1-yne?
Originally posted by Vitalitylx:for qn 2, what about C-C bond forming head on with p-orbital since its hybridised?
Oh, so in this case question 2 is interpreted to only talk about unhybridized orbitals? Hence D is the answer?
Originally posted by Vitalitylx:Oh, so in this case question 2 is interpreted to only talk about unhybridized orbitals? Hence D is the answer?
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.
Originally posted by Ibenedictkoh: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.
Answers for 2015 9646/01 H2 Physics MCQ:
1) A 2) D 3) C 4) A 5) C
6) A 7) D 8) C 9) A 10) C
11) B 12) A 13) D 14) A 15)A
16) A 17) C 18) C 19) C 20) B
21) C 22) D 23) B 24) B 25) A
26) B 27) B 28) B 29) D 30) B
31) B 32) D 33) B 34) C 35) C
36) C 37) C 38) A 39) D 40) B
Credits: Oliver Cheok, Chua Wei Pin, Huang Tao, Wee Wen Jun
The people above hold no liability for any possible errors. Do inform us about any errors below!
Whats hybridised and unhybridised orbitals?
Hybridised means formed bond alr, unhybridised haven't?
For qn 21 , i identified pentyne , pent-2-yne, 3-methylbut-2-yne, 3 methylbutyne
Which one of my identified structural isomer(s) are wrong?
Originally posted by Flying grenade:Whats hybridised and unhybridised orbitals?
Hybridised means formed bond alr, unhybridised haven't?
For qn 21 , i identified pentyne , pent-2-yne, 3-methylbut-2-yne, 3 methylbutyne
Which one of my identified structural isomer(s) are wrong?
Hi thank you so much for doing this! Really appreciate it! :)
May i know what is minimum % to get A for H3 pharm. chem? As in what is the traditional boundary? Just had my paper today and it was easier than past yr paper. Really scared that i will get bell-curved by all the zai ppl out there. Thank you once again!!
Your sincerely