Wjec ch4 2013

Aargh I found it horrible! Worse than most past papers I've done :frown:

What did people do for the question about a test to determine between the two different molecules, think it was methylchlorobenzene and 1,4-chlorobenzene?

I put reflux both with NaOH(aq) to produce the alcohol from the aliphatic chloroalkane. Then oxidise with dichromate (VI) in dil. H2SO4. the colour change would represent the presence of the alcohol and the para/1, 4- dichloro benzene would not induce a colour change from orange to green. :colondollar:

I had to think that through quite a bit though.
also it would have worked if you reflux with NaOH and then add silver nitrate and white ppt would indicate presence of Cl- ions :smile:

Reply 41

Arthurnator

Original post by Lloydm17

What did every one go for the order of acidity question? :confused:

I put:
phenol allows the lone pairs of electrons on the oxygen to be de-localised into the benzene ring therefore promoting the formation of the phenoxide ion thus liberating/disassociating a proton. The Phenoxide ion will rarely be re-protonated.

And for the amine i said there's 3 bond pairs on the nitrogen and one lone pair of electrons. Allowing it to accept a proton and form a coordinate bond with hydrogen and creating a salt therefore acting as a base

Reply 42

JonnieBevan

Any ideas what the (5) marks would be for in the polymer question? Thrown off by the obscene descriptions, synthetic and natural? Yeah because they're in the syllabus. *sarcasm* WJEC are the worst exam board for that.

Reply 43

shawneexo

Original post by Arthurnator

I put reflux both with NaOH(aq) to produce the alcohol from the aliphatic chloroalkane. Then oxidise with dichromate (VI) in dil. H2SO4. the colour change would represent the presence of the alcohol and the para/1, 4- dichloro benzene would not induce a colour change from orange to green. :colondollar:

I had to think that through quite a bit though.
also it would have worked if you reflux with NaOH and then add silver nitrate and white ppt would indicate presence of Cl- ions :smile:

Oohh I want your brain :colone:

I got the silver nitrate and white ppt bit but missed out the NaOH which is annoying -.-

Reply 44

shawneexo

Original post by JonnieBevan

Any ideas what the (5) marks would be for in the polymer question? Thrown off by the obscene descriptions, synthetic and natural? Yeah because they're in the syllabus. *sarcasm* WJEC are the worst exam board for that.

I put nylon 6,6 as the synthetic one, with the dicarboxylic acid and diamine thats needed, then I put a polypeptide for the natural one and used alanine and glycine (but their systematic names) :smile:

Reply 45

JonnieBevan

Original post by shawneexo

I put nylon 6,6 as the synthetic one, with the dicarboxylic acid and diamine thats needed, then I put a polypeptide for the natural one and used alanine and glycine (but their systematic names) :smile:

So putting a polyester for synthetic wasn't right then? :frown:

It was a guess at the end of their day, the question never asked me to name the molecules or even say what polymer they were a part of so I'm not too worried, it's a shame there's almost a grade boundary relying on a single point in the syllabus! :angry:

Reply 46

shawneexo

Original post by JonnieBevan

So putting a polyester for synthetic wasn't right then? :frown:

It was a guess at the end of their day, the question never asked me to name the molecules or even say what polymer they were a part of so I'm not too worried, it's a shame there's almost a grade boundary relying on a single point in the syllabus! :angry:

Yeah I think a polyester would be right too, that can still be synthetic! so cheeer up ahah :smile:

Reply 47

stevo95

Original post by Arthurnator

I put reflux both with NaOH(aq) to produce the alcohol from the aliphatic chloroalkane. Then oxidise with dichromate (VI) in dil. H2SO4. the colour change would represent the presence of the alcohol and the para/1, 4- dichloro benzene would not induce a colour change from orange to green. :colondollar:

I had to think that through quite a bit though.
also it would have worked if you reflux with NaOH and then add silver nitrate and white ppt would indicate presence of Cl- ions :smile:

I did that... With the acidified potassium dichromate!!! Is that right?

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Reply 48

ellaott

1

Cannot believe how horrible that exam was, wjec are such sly dogs. Anyone else feel the same?

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Reply 49

JonnieBevan

Original post by shawneexo

Yeah I think a polyester would be right too, that can still be synthetic! so cheeer up ahah :smile:

Haha, I'm really not that worried about the exam, the rest of it went really well, even better after reading through this. I always seem to concentrate on the negatives of an exam.

Reply 50

shawneexo

Original post by JonnieBevan

Haha, I'm really not that worried about the exam, the rest of it went really well, even better after reading through this. I always seem to concentrate on the negatives of an exam.

Ahh good, glad it went well! I have a friend who is exactly the same haha, bloody pessimists :P

Reply 51

Arthurnator

Original post by stevo95

I did that... With the acidified potassium dichromate!!! Is that right?

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I don't see how it wont work :smile:

Reply 52

Arthurnator

Original post by JonnieBevan

Any ideas what the (5) marks would be for in the polymer question? Thrown off by the obscene descriptions, synthetic and natural? Yeah because they're in the syllabus. *sarcasm* WJEC are the worst exam board for that.

I totally agree. However I put nylon 6 as synthetic simply to save time with only having to draw one monymer ( in the circle monymer structure) and glycene (the most simple amino acid with H as an R group) which polymerise in biological systems. Examples of each is at least 2 marks each
Then another 1 for correct structural formula of repeating unit and monymer and for the final mark I think it just isolating the specific linkages like ester and amide links. I know this is more than 5 but in the mark schemes there are more right answers that marks available if I'm making any sense

Reply 53

JonnieBevan

Original post by Arthurnator

I totally agree. However I put nylon 6 as synthetic simply to save time with only having to draw one monymer ( in the circle monymer structure) and glycene (the most simple amino acid with H as an R group) which polymerise in biological systems. Examples of each is at least 2 marks each
Then another 1 for correct structural formula of repeating unit and monymer and for the final mark I think it just isolating the specific linkages like ester and amide links. I know this is more than 5 but in the mark schemes there are more right answers that marks available if I'm making any sense

Yeah, you're probably right. Didn't think about that really, there were a couple of the longer essay style questions so there should be plenty of chances to pick up marks! Thanks

Reply 54

Rennie Akoni

Original post by shawneexo

Aargh I found it horrible! Worse than most past papers I've done :frown:

What did people do for the question about a test to determine between the two different molecules, think it was methylchlorobenzene and 1,4-chlorobenzene?

I left this question out!! which is soo annoying because then I realised that I new the answer! The 1,4-chlorobenzene won't react with sodium hydroxide with the methylcholorobenze will. Because the C-Cl bond on the benzene is really strong because of the pi bonds blah blah blah

Reply 55

emkate

Original post by Arthurnator

don't worry they will give you credit for the presence of the function groups in the right place :smile:

Ah I hope so! Thank you :smile:

Reply 56

SheldonBlooper

Overall, thought the paper was horrid. So much synoptic assessment it was unreal. Loads of questions which relied on knowing the most obsecure tiny facts. Hated the whole "extended writing" style of the paper and overall just a fairly poor paper. Looks like i'm gonna have to resit in June :frown:

Reply 57