Edexcel A2 Chemistry 6ch04/05 JUNE 2015

I haven't really come across a proper synthesis question where they ask you how to make this from that- with loads of steps (maybe only one question in a recent paper)? is this something from unit 6?

Lots of questions on Azo dyes and all other other reactions so knowing them all will cover all you're bases

I haven't really come across a proper synthesis question where they ask you how to make this from that- with loads of steps (maybe only one question in a recent paper)? is this something from unit 6?

The most synthesis-y question I have seen was when they asked to me to give the full process for chromatography for identifying amino acids - 7 marks, and I just wrote every point from memory.

the answer is D, but I don't understand what's going on, any help would be appreciated thanks

the answer is D, but I don't understand what's going on, any help would be appreciated thanks

Aldehyde and carboxylic acid groups are reduced to alcohol groups. (reverse of the potassium dichromate reaction)

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Look at this link to understand what's going on
http://www.chemguide.co.uk/organicprops/carbonyls/reduction.html

Thank you, what's the addition of acid going to do?

It's part of the mechanism.
So the reducing agent first breaks the oxygen double bond to leave a negatively charged oxygen which is singly bonded to the carbon, as well as donating a hydride to the carbon too. The addition of the acid then protonates the oxygen to form the hydroxide group. This is done with acid rather than reducing agent because the acid donates H+ whilst the reducing agent can only donate H-.

suppose the overall equation for a reaction is: 2A+B----------> C; how do we:
. say that this reaction involves more than one steps
.find the RDS or the slow step???
Anyone???

Thanks in advance!

are you sure you haven't left out any part of the question? which paper?

suppose the overall equation for a reaction is: 2A+B----------> C; how do we:
. say that this reaction involves more than one steps
.find the RDS or the slow step???
Anyone???

Thanks in advance!

wow are we supposed to know this? because i'm looking at the spec right now and they don't say anything about mechanisms on this particular reduction/oxidation reaction

There would be more information to it... So if, for instance, there was only one of A or B involved in the rds, you would conclude there must be a second step in which the other molecule reacted in. Youd find the rds experimentally, there's no other way to do it.



There was a question I saw about how reducing agents work, not so much the mechanism though. I can't remember the paper. I've only learnt it because it's helped me understand the need for acid so there's one less thing to rote learn

aha yup totally with these chemistry units it would do no harm to learn the "behind the scenes" given the unpredictable nature of edexcel exams thanks

For some reason I just cannot get my head around these calculations So I have worked out the moles of thiosulphate, but the mark scheme jumps straight into ''moles of Cu2+ in 25cm^3 sample = moles of thiosulphate'', I just can't see how to work this out :-( I'm probably being really silly, but could somebody please point me in the right direction

those are moles in 25cm3 so you must multiply moles of 25 by 10 to get moles in 250

let me know if you want me to work it out for you