2014 H2 Chemistry Paper 2, Paper 3 and Paper 1 discussions

last SG · 2014-11-17T21:59:01+00:00

Guys I know this is a chem discussion page but can someone post their answers for Bio MCQ today? :S Think I'm gonna get 33/34 crying

UltimaOnline SG

Regarding calculation answers, as mentioned earlier, some JCs and some other private tutors will probably make the full solutions available online sometime. Don't worry about calculation answers. As long as you showed clear working, Cambridge will give you some marks even if you made careless mistakes.

"For peroxyethanoic acid I think perhaps the only difference being an additional O makes the distance to C=O further hence the dispersal of the negative charge conjugate base occurs to a lesser extent. Only difference and possible reason I guessed."

No. As mentioned in a preceding post in this thread, the correct reason for the lower acidity of peroxycarboxylic acid, is that unlike carboxylic acid, the peroxycarboxylate conjugate base *cannot* be stabilized by having it's negative formal charge delocalized by resonance over 2 O atoms (as is the case with regular carboxylate conjugate bases). Stabilization by resonance delocalization of charges require conjugation, ie. sideways overlapping of unhybridized p orbitals, which is not present due to a sp3 O atom between the O- atom and the sp2 C atom.

UltimaOnline SG

No worries. Should be ok.

Holy shit i juz realised i forgot to label my last structure, for qn5. i labelled everything from x y and z then i forgot to put the sign for the last one. sir will they deduct? its basically the last structure....

Alohamadda SG

wa i damn scared later they minus marks... for utter stupidity...

UltimaOnline SG

No prob. As you well-advised your peers, you students shouldn’t be too worried by all the “Sooooo easy! ‘A’ grade confirm over 80% liao!”. ‘A’ grade cut-off will remain 75% this year. Mark my words.

mrchn SG

I already explained the 'real' reasons in preceding posts.

D: I couldn't find.. but anw since you reposted alr haha thanks! :) but umm intramolecular hydrogen bonding is possible even if molecule is linear?

UltimaOnline SG

D: I couldn't find.. but anw since you reposted alr haha thanks! :) but umm intramolecular hydrogen bonding is possible even if molecule is linear?

First of all, the molecule isn't linear. Secondly, you're right that the bond angles are still not ideal. But for A level purposes, Cambridge will accept intramolecular hydrogen bonding as the reason.

UltimaOnline SG

Ok, I’m gonna afk for the night liao. But feel free to continue discussing with each other. This includes posting any queries you may come across in your preparation for P1.

mrchn SG

shittt I'm so stupiddddd HAHAHAA thankssss!! :D

Alohamadda SG

need to know ez priority?

UltimaOnline SG

need to know ez priority?

Not for H2 syllabus. Even if it's E-Z rather than cis-trans, just say "geometric isomers" you'll get the mark liao.

Adelineeeee (: SG

Does anyone have any idea on the mark range for B? oh and how did u guys find paper2? Many ppl said it was easy but i find the questions asked pretty weird ):

Angelofv3rdun SG

How to draw the P2N2Cl6 ??

Newcomer99 SG

Hi I'm wondering if my answers for 1c can be accepted:

H2o2 is more acidic because its conjugate base is more stable due to the dispersion of the negative charge over 2 electronegative oxygen as compared to one for water.

Peroxyethanoic acid is less acidic due to intramolecular h bonding which makes it less easy to be deprotonated.

Ty:)

Matthewsoemoz SG

Hi Ultima!

what questions did you do :)

Helloheyho SG

Question 3cii why not alkyne (triple bond)? It fits the molecula formula and will be reduced to pentane by H2 Ni too.

BUTTanalALDEHYDE SG

Hi!! For question 1c, is it possible to argue for H2O2 to be more acidic because the negative charge on conjugate base can be delocalised among the two electronegative oxygen atoms?

horny nucleophile SG

Ok, I’m gonna afk for the night liao. But feel free to continue discussing with each other. This includes posting any queries you may come across in your preparation for P1.

waky waky mr heng ;D matthew asks you to prepare $150 ;D

Matthewsoemoz SG

waky waky mr heng ;D matthew asks you to prepare $150 ;D

I dont think i have enough activation energy to accomplish such a massive feat.

UltimaOnline SG

Hi I'm wondering if my answers for 1c can be accepted:

H2o2 is more acidic because its conjugate base is more stable due to the dispersion of the negative charge over 2 electronegative oxygen as compared to one for water.

Peroxyethanoic acid is less acidic due to intramolecular h bonding which makes it less easy to be deprotonated.

Ty:)

Your H2O2 answer ok, your peroxycarboxylic answer not ok. I posted the correct reason earlier in this thread liao.

UltimaOnline SG

How to draw the P2N2Cl6 ??

Cl3P=N-N=PCl3

or

(Cl)2PN(Cl)N(Cl)P(Cl)2

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