Debrief - 9746 Chemistry
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zzz. lost 5 marks because i thought carbonates were considered as carbonyls T_T
but other than that still manageable. a bit harder than i expected though. -
ho ho ho!!! song bo liao... all the ratio question one, i dunno how to do sia.. lol anyhow put them. i did Qn 1,2 ,3 and 4. Qn 5 to me.... is an alien question bcoz i suck at Protein questions..
overall still abit hard la~ -
do we write the theoretical ratio of 6:4 for 1bromo n 2bromo or the realistic one whereby 2bromo is higher than 1bromo?
btw hi everyone my first time here! -
3:2 i think. that's what i wrote anyway. in actual fact, the stability of the secondary radical is outweighed by the increased chances of 1bromobutane being formed.Originally posted by xxxshadowxxx:do we write the theoretical ratio of 6:4 for 1bromo n 2bromo or the realistic one whereby 2bromo is higher than 1bromo?
btw hi everyone my first time here! -
yup..3:2 is the original one..bt i wrote 3:7 which is the experimental one stated in my notes..nvm..i think mayb the answer will depends on ur explaination tt followsOriginally posted by teraexa:3:2 i think. that's what i wrote anyway. in actual fact, the stability of the secondary radical is outweighed by the increased chances of 1bromobutane being formed. -
hi guys, im new here too
btw, i think the paper was horrible...
im counting on proteins actually
r u talking bout the 3 carbonyl compounds? any idea what are those 3?Originally posted by teraexa:zzz. lost 5 marks because i thought carbonates were considered as carbonyls T_T
but other than that still manageable. a bit harder than i expected though.
i got propanone, propanal, methanal
but then i cant distinguish between methanal and propanal
so i guess theyre wrong?
also whats the type of reaction when amide becomes N- Na+?? -
i use fehling's solution to distinguish between aldehyde n ketone..tollen's oso canOriginally posted by plasticpiranha:hi guys, im new here too
btw, i think the paper was horrible...
r u talking bout the 3 carbonyl compounds? any idea what are those 3?
i got propan-1-one, propan-2-one, methanal
but then i cant distinguish between methanal and propan-1-one -
the 3 correct ones should be methanal, ethanal and propanone.Originally posted by plasticpiranha:hi guys, im new here too
btw, i think the paper was horrible...
im counting on proteins actually
r u talking bout the 3 carbonyl compounds? any idea what are those 3?
i got propanone, propanal, methanal
but then i cant distinguish between methanal and propanal so i guess theyre wrong?
also whats the type of reaction when amide becomes N- Na+??
to distinguish propanone, just use Tollens' as it won't give silver mirror.
then between methanal and ethanal, add aqueous alkali iodine. ethanal will give yellow ppt while methanal won't.
When amide becomes N- Na+, it is an acid-base/neutralisation reaction (your sodium salt). -
oops i made a mistake in naming just now :p (editted the post)Originally posted by xxxshadowxxx:i use fehling's solution to distinguish between aldehyde n ketone..tollen's oso can
how do you know which 3 carbonyls are formed?
and how come ethanal is formed? the no of C atom doesnt tally then? -
My friend say....its not ethanal.....its ethanoic acid...... and ethanoic acid has a carbonyl group as well....he gave a lot of explanation and I still don't understand at all....=/Originally posted by teraexa:the 3 correct ones should be methanal, ethanal and propanone.
to distinguish propanone, just use Tollens' as it won't give silver mirror.
then between methanal and ethanal, add aqueous alkali iodine. ethanal will give yellow ppt while methanal won't.
When amide becomes N- Na+, it is an acid-base/neutralisation reaction (your sodium salt).
This paper is like my school's standard I feel...if not harder....and I nearly failed for my school's prelim chem paper 3 -
Originally posted by tangjing:
he trying to scare u
My friend say....its not ethanal.....its ethanoic acid...... and ethanoic acid has a carbonyl group as well....he gave a lot of explanation and I still don't understand at all....=/
This paper is like my school's standard I feel...if not harder....and I nearly failed for my school's prelim chem paper 3 -
wiki says that tertiary radical > secondary radical > primary radical in terms of stability. so it is like 2-bromobutane is the major product rather than 1-bromobutane. if i did not interpret wrongly, that is it.
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Quite hard man..... Cambridge really transform into something new liao
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so in this case, how would you be able to approximate the ratio?Originally posted by th3m0ment:wiki says that tertiary radical > secondary radical > primary radical in terms of stability. so it is like 2-bromobutane is the major product rather than 1-bromobutane. if i did not interpret wrongly, that is it.
this is the a levels. let's not think too much extra-A-levels stuffs. keep it SAD (Simple And Direct). -
That reaction cannot form ethanoic acid.Originally posted by tangjing:My friend say....its not ethanal.....its ethanoic acid...... and ethanoic acid has a carbonyl group as well....he gave a lot of explanation and I still don't understand at all....=/
This paper is like my school's standard I feel...if not harder....and I nearly failed for my school's prelim chem paper 3
http://www.chembook.co.uk/chap22.htm
Check for section "22.3.10. Other reactions of carboxylic acids and their salts."
"Calcium methanoate gives methanal on heating, whereas the calcium salts of other carboxylic acids give ketones. If calcium methanoate is heated with the calcium salt of another carboxylic acid, the products will be mixed eg calcium methanoate plus calcium ethanoate will give methanal, propanone, and also ethanal." -
how are we supposed to know this? its nowhere in the syllabus i can think of...Originally posted by teraexa:"Calcium methanoate gives methanal on heating, whereas the calcium salts of other carboxylic acids give ketones. If calcium methanoate is heated with the calcium salt of another carboxylic acid, the products will be mixed eg calcium methanoate plus calcium ethanoate will give methanal, propanone, and also ethanal."
cambridge is really trying to kill us...
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I guess they want us to learn the art of deduction.Originally posted by plasticpiranha:how are we supposed to know this? its nowhere in the syllabus i can think of...
cambridge is really trying to kill us... -
i just give a ratio that is larger for 2-bromo..cos i tink there is not much stuff to explain this ratio if u write the theoretical 3:2..n it is indeed true that 2-bromo is the major pdtOriginally posted by teraexa:so in this case, how would you be able to approximate the ratio?
this is the a levels. let's not think too much extra-A-levels stuffs. keep it SAD (Simple And Direct). -
Er i derived the 3:2 from the fact that the possible C-H bonds that can be substituted with a Br atom.Originally posted by xxxshadowxxx:i just give a ratio that is larger for 2-bromo..cos i tink there is not much stuff to explain this ratio if u write the theoretical 3:2..n it is indeed true that 2-bromo is the major pdt
There are 6 such places for 1-bromobutane and 4 such places for 2-bromobutane. -
teraexa which jc u from??u seem so lihai..ahhh think the time restrain of the paper make it tough
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now i need to count on Paper 2 and MCQ to secure a B...
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ethanoic acid does not have a carbonyl group, but a carboxylic acid groupOriginally posted by tangjing:My friend say....its not ethanal.....its ethanoic acid...... and ethanoic acid has a carbonyl group as well....he gave a lot of explanation and I still don't understand at all....=/
This paper is like my school's standard I feel...if not harder....and I nearly failed for my school's prelim chem paper 3 -
ya..bt i tink the explaination abt the secondary radicals being more stable is more suitable n technical..cos i was following wat was given in notes..all in all the problem lies wif the question..did not state clearlyOriginally posted by teraexa:Er i derived the 3:2 from the fact that the possible C-H bonds that can be substituted with a Br atom.
There are 6 such places for 1-bromobutane and 4 such places for 2-bromobutane. -
which other jc will the chem dept force-feed and drill chem stuffs into your until you resemble nothing more than battery farm animals stuffed with chemical additives ready to be sent to the slaughterhouse known as A levels chemistry?Originally posted by duperlicious:teraexa which jc u from??u seem so lihai..ahhh think the time restrain of the paper make it tough
of course it's rjc. -
haha..nice descriptionOriginally posted by teraexa:which other jc will the chem dept force-feed and drill chem stuffs into your until you resemble nothing more than battery farm animals stuffed with chemical additives ready to be sent to the slaughterhouse known as A levels chemistry?
of course it's rjc.