sua la over alr sian mcq juz pia lor.... sian my fren all score so high...
Originally posted by mrchn:
and does anyone know what's the real reason pKa of H2O2 is lower and peroxyethanoic acid is higher? lol totally didn't have any idea of what to write.. are we even supposed to know this
Hello my fellow A-level warriors. First time on the forum~!
I am from the upper tier schools and I personally found it manageable and comparable to past year papers, hopefully it can make up for the egregious numbers of careless mistakes in my paper 2. My school mates all around did actually say it was challenging so don't fret if you didn't feel confident about your answers, hopefully we can all work hard together for paper 1 which should be the last or last few papers for most of us next week. Not too sure about calculations though until the numerical answers are available but the organic mechanisms were decently manageable. (Haha sir would you mind if you can post numerical answers for the calculations after you did the paper)
Did question 1,2,4,5 because I took a quick glance at 3 and found b and the last few parts of d challenging and decided to give it a miss and go with the safer option of 2 because I was stumped at question 5 and only had 25 minutes for the last question but luckily managed to finish just when the invigilator called for time.
I think the reduction of esters into 2 alcohol groups may seem very out of syllabus to us and you have every right to feel aggrieved that such a question appeared but ultimately Cambridge is only given our syllabus and learning outcomes so we cannot exactly blame them for not knowing what is in our lecture notes or not. Ultimately there were a few clues in the question like one of them being chiral and L being definitely chiral must mean that M would not be chiral and hence two similar groups must be present. I personally did encounter reduction of esters in a 2014 prelim paper before and was vaguely remembering what is formed, so I confirmed it by using the degree of unsaturation formula which many schools have tested before and you would have likely come across it during your topical practice. There are also many weird questions where for example we are taught that hydrogenation of alkenes require high temperature and pressure but in question 5 room temperature is utilised which contravenes what we learn. So end of the day, Chemistry is really about applying all our knowledge in some form or another to be able to counter Cambridge out of the blue tricks here and there, also I believe the vettors at SEAB are teachers before and cognisant of what we learn so they wouldn't be so heartless as not to drop any hints in the question.
For H2O2 I wrote stabilisation by intramolecular hydrogen bonding as well because I remember Cambridge tested some form of it last year in the last question of paper 3 I think, not too sure whether it is the right way to explain but thankfully UltimaOnline has clarified our worry.
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.
Jia you guys don't fret about what is done, some people have good days and bad days but there is a margin of error for the higher grades so not too worry. I personally flung paper 2 quite badly by making numerous careless mistakes.
Also, don't bother about what your friends say, many of them may be masking their true feelings and deep inside know truthfully how well they did. Those who gloat and not care about others' emotions aren't really nice people you should be around then. Remember, "Those who don't mind (your feelings) don't matter, those who mind matter". Jia you for paper 1 and your remaining papers.
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....
Originally posted by Alohamadda: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....
Thank you sir. I think I'd probably got that question wrong after your explanation, but nevertheless thank you for the clarification
wa i damn scared later they minus marks... for utter stupidity...
Originally posted by UltimaOnline:
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?
Originally posted by mrchn: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?
Originally posted by UltimaOnline:
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.
shittt I'm so stupiddddd HAHAHAA thankssss!! :D
need to know ez priority?
Originally posted by Alohamadda:need to know ez priority?
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 ):
How to draw the P2N2Cl6 ??
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:)
Hi Ultima!
what questions did you do :)
Question 3cii why not alkyne (triple bond)? It fits the molecula formula and will be reduced to pentane by H2 Ni too.
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?
Originally posted by UltimaOnline: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
Originally posted by horny nucleophile: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.
Originally posted by Newcomer99: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:)