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AQA Chem (mod 4,5 and 6 discussion)

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Reply 20

all_or_nothing

sunday

I know

Highest I've got so far is 24/40, I then go back and check through with the right answers, and most of the time I can't even figure out how they got the answer they did!

Thats like opposite to me. Have only done one of unit 6 papers and that was my mock and got 20 (a lot better than I thought). Then when I went and looked it over, realised that loads of the answers were really obvious!
I don't like this exam! Its too rushed too!

Reply 21

jellytotz

wow 20! i did a one an got 11! :frown:

...theres no hope..

Reply 22

all_or_nothing

of course there is hope.
You still have over a week and there are loads of past papers on the aqa website. So have a go at those and keep revising everything.
What sort of grade do you need to get on this paper?
You could concentrate maybe on only the first 30 questions or something.
I mean its surely better to do 30 well, than rush and do 40 not so well. You can always guess the last ten. Depends what your aiming for i suppose.
Just keep at it.

Reply 23

Maestor

essay = mechanisms :biggrin:

Reply 24

sunday

I just hadn't anticipated the amount of organics from mod 3 that comes up! I can barely remember it from mod 4 in Jan. Attempting to learn all mod 3 organic mechanisms today haha :frown:

Reply 25

Maestor

learning them for module 5 + 6 u mean?...because i dont think all Mod 3 mechanisms come up on module 4

Reply 26

Ghetto_Princess12

Maestor

learning them for module 5 + 6 u mean?...because i dont think all Mod 3 mechanisms come up on module 4

For module 4 you don't need to know any of the mechanisms from module 3, but module 4 does have some bits of module 3 such as alcohols, isomerism and amines and polymers.

Reply 27

sunday

Nah I'm on about for mod 5 and 6, loads of past papers have mod 3 organics in them, some for around 10 or so marks! Not doing mod 4 again thank goodness :smile:

Reply 28

Maestor

actually for module 4 you have to know Nucleophilic Addition.. :smile:

Reply 29

all_or_nothing

No the mark scheme is correct. Give me a mintue and I'll type out how I worked it out..

Reply 30

dimz

o wait i think I get it but ok all or nothing.

Guys can someone explai nthe whole what happens to kp and kc when there is an increase in volume?

Reply 31

all_or_nothing

Ok, so you know that X + Y gives A by using H2SO4.

Straight away I think, what do I know that uses H2S04 between two compounds which produce an isomer with two Oxygens in?

This would be an esterification reaction, between an acid and an alcohol.

Then, X and Y are formed from propanal (which means X can't be propanal as you said)

Think back to the first part, one of X and Y could be an acid, which makes sense because an aldehyde (like A) can form an acid if reacted with acified potassium dichromate.

Also, A has an absorption at 1750 cm-1, which means it has C=O bond. This suggests to me that A is a carboxylic acid. So it must be propanoic acid. (It can't be propanal because that's what you started with)

B could then be an alcohol (as we have now confirmed that A is an acid, meaning that the inital thought that X + Y is an esterification is correct)

An aldehyde + NaBH4 gives an alcohol, so Y is propanol.

This is confirmed in that CH3CH2CH2OH (propanol/Y) + CH3CH2COOH (propanoic acid/X) = CH3CH2COOCH2CH2CH3 (propyl propanoate)
which has molecular formula C6H12O2 (as given in question)

Dimz - hope that this makes some sense or helps you to understand the mark scheme.

Reply 32

all_or_nothing

Ok, so you know that X + Y gives A by using H2SO4.

Straight away I think, what do I know that uses H2S04 between two compounds which produce an isomer with two Oxygens in?

This would be an esterification reaction, between an acid and an alcohol.

Then, X and Y are formed from propanal (which means X can't be propanal as you said)

Think back to the first part, one of X and Y could be an acid, which makes sense because an aldehyde (like A) can form an acid if reacted with acified potassium dichromate.
Also, A has an absorption at 1750 cm-1, which means it has C=O bond. This suggests to me that A is a carboxylic acid. So it must be propanoic acid. (It can't be propanal because that's what you started with)

B could then be an alcohol (as we have now confirmed that A is an acid, meaning that the inital thought that X + Y is an esterification is correct)

An aldehyde + NaBH4 gives an alcohol, so Y is propanol.

This is confirmed in that CH3CH2CH2OH (propanol/Y) + CH3CH2COOH (propanoic acid/X) = CH3CH2COOCH2CH2CH3 (propyl propanoate)
which has molecular formula C6H12O2 (as given in question)

Dimz - hope that this makes some sense or helps you to understand the mark scheme.

Yes its does lead to the formation of a carboxlic acid (as I said above 'acid' being my shorthand for carboxylic acid)

As for NaBH4, that is used to turn an aldehyde/acid back to an alcohol (i.e. it does the reverse of potassium dichromate) It's on p227 of AQA AS Chemistry textbook

Reply 33

dimz

ok cool, what bout my amino acids query

Reply 34

all_or_nothing

No I don't think you need to know how each one looks, you definitely need to know the general formula for an alpha amino acid. In the specification it doesn't say anything about learning structures.

Reply 35

sophia786

Hey guys
i don't know if this is a fact but apparently you need mid 20's to get a grade A on module 6
do they really lower the grade boundaries?

Reply 36

Ghetto_Princess12

sophia786

Hey guys
i don't know if this is a fact but apparently you need mid 20's to get a grade A on module 6
do they really lower the grade boundaries?

Where did you find out about that? If you look at the previous examination reports then you'll find the end page will have the grade boundaries and to get an A grade you need approximately 33/40.

Reply 37

Ghetto_Princess12

dimz

alpha amino acid? whats that.

I think the two things I have problems with are those ph graphs and what the hell is equivalence point.

For the amino acids you'll need to know the structures of the zwitterions at different PH levels. So for example If you increase the pH of the solution by adding an Alkali then the structure of the amino acid changes and you'll need to be able to draw that. If you decrease the pH by adding an acid to a solution of an amino acid then structure again changes and you need to be able to draw that too.

Reply 38

Ghetto_Princess12

dimz

alpha amino acid? whats that.

I think the two things I have problems with are those ph graphs and what the hell is equivalence point.

I never understood PH graphs at the first but gradually as you progress you kind of get the concept of it. All you need to do is learn the graphs for strong/weak acid and strong base/weak.

Reply 39

all_or_nothing

sophia786

Hey guys
i don't know if this is a fact but apparently you need mid 20's to get a grade A on module 6
do they really lower the grade boundaries?

It would b nice is they did! :rolleyes:

But I haven't heard anywhere that they do though. When we did our mock the grade boundaries were on percentages, like 80%=A, 70%=B, so for an A you would need 32/40. But remember that coursework gets added in too and then they scale it up to out of 90 or something (maybe 120 on this one). I guess if everyone does badly then the marks get scaled up more, so you could think of it as grade boundaries being lowered.