OCR Chemistry A 2017 Exam Thread (New A Level)

Not to worry. Found it.

So this is what the question said:

Fruit Juice contains a mixture of ORGANIC ACIDS.

( This is where I slipped up, but when a question mentions organic acid, they're referring to COOH).

So We have Acid C, an aliphatic organic acid present in the fruit juice.

Aliphatic denoting containing carbon atoms joined together in a straight or branched chain.

1.21*10^-2 mol C has a mass of 2.323 g.

So, lets start off with working out the Mr of C.

Mr of C: 2.323/ 1.21*10^-2 = 191.984711 or 192 g mol^-1 (3.s.f.)

The question tells us that 1 mol of acid C requires 3 mol NaOH for neutralisation. This denotes that acid C must have 3 COOH groups.

So we subtract the Mr of COOH groups and the OH group from the Mr we found. This is because the question mentions that the acid C also contains a hydroxyl group. Additionally, the Acid C contains a hydroxyl group but produces no colour change with hot acidified dichromate. This denotes that it's a 'tertiary alcohol', as tertiary alcohols cannot be oxidised and thus the O-H group must have three alkyl groups attached to its carbon atom to which the hydroxyl group is attached to

Mr of COOH= 45
Mr of O from hydroxyl group = 16

The molecular formula of C is C x H y O 7

Lets remove the Mr of the oxygen atoms in order for us to obtain just the C x H y part.

192- (3*45) - 16= 41

Therefore C x H y = 41

Therefore C x H y must be C3 H5

Now the question also mentions that there are 4 peaks in the 13 C NMR spectrum and thus we must have 4 different types of carbon environments.


This denotes that the molecule must be:


COOH-CH2- C(COOH)(OH)- CH2- COOH

( I know thats not correct notation of a molecular formula, I just want you to be able to see what the structure would look like. Note that the COOH OH groups are attached to the same carbon.

And there you have it.

How did people find the unlocked unified paper?


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How did people find the unlocked unified paper?


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Similar difficulty. But weirdly my unified is my strongest paper compared to paper 1 and 2 😂

Does everyone know about the 3 bonds apart rule in proton NMR, was covering it as i felt there was a slight gap in my knowledge and this rule brought it all together.

14 Which substance(s) experience(s) induced dipole–dipole interactions (London forces)?





Your answer

[1]
hey that was a question on one of the practice papers the correct answer is B but in the pearson book it says "london forces exsist in molecules but are only considered when there a re no other intermolecular forces at play" can anyone explain to me why SiO2 does not have london forces (or could it be a mistake in the mark scheme)

SiO2 is a GIANT covalent lattice where all the atoms are joined together by covalent bonds. That's the force present between the atoms. SiO2 is not a molecule but a giant lattice.

whats your weakest?

Never heard of it could you explain it or its use?

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Paper 1

when your looking at a proton directly attached to a carbon atom (so that proton environment) if there is no protons adjacent within three bonds there will be no splittings, im not sure how to explain it i can send you the link though its ocr relevant if you want? it helped a lot for me for the harder table questions where you fill in a table asking for the relative area, splitting etc..

Could I please have that link too


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https://www.youtube.com/watch?v=9btbezNOI68 this guys really good you probably already know of him, he starts to talk about it from 1:40

how when you got 82/100? lol thats pretty good on a practice paper which everyone seems to be doing bad in, but for me organic is the best, then physical then synoptic.

Sorry I got 82/100 on paper 2 not 1!! Paper 1 I just got back and failed hahahah

Thanks, just watched it and it makes more sense now : )


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what you doing for biology? im stressed out for that subject im still brushing up on biotech and ecosystem then i have to recap on mod 4 all over again too plus PAPERS!!!