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# OCR Chemistry B (Salters) F334/F335 Exam Thread 2016 (14th/22nd June)

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1. (Original post by IBerrr)
For the 5 marker of bromine this is the method I used:

After working out the moles of BrO3- in the previous question (= 0.005 moles and so was in excess) and looking at the reaction equation given, you know that the ratio of BrO3- was 1:3 for Br2, so the moles of Br2 is 3x0.005 = 0.015

We also know that it was 0.015 moles of br2 in 200cm3, but the hexadiene molecule only reacts with 83, so 0.015/200x83? I think

So that's the moles of br2 reacted is worked out, so you multiply that by mass of bromine and then x2 because two bromine molecules.

Lastly you times that by 10 because for bromine number it is of 100g of hexadiene whereas the question said 10g.

I don't know if this is right, this is just what I did. Anyone do the same?
BrO3- was in excess, wasn't it? So You had to use the moles of Br- to calculate the moles of Br2 (by dividing by 5 and multiplying by 3). I'm not 100% sure but that is what I did.
2. It wasn't 10 bc when calculating the conc of Br2 you had to use the moles of Br- since that was not in excess... Sadly I used the excess bromate ions moles so I got 10 too T_T
3. (Original post by josephinemar25)
No it was a partial hydrolysis that only broke one amide bond
Why was it partial hydrolysis? I don't remember reading that?!?! I drew 3 molecules and also I'm 90% sure the question was 3 marks
4. I knew the rate equation was familiar...
Attached Images

5. This was such a nice paper compared with last years
6. (Original post by Zuzuvela)
Grade boundaries should be around 56 for an A. That's not unreasonable considering the paper Look at how many of the questions had not come up before in any way shape or form. First time I've seen cold drawing, First time I've seen 10marks worth of maths in one question (bromine number). First time recrystallisation has ever been 3 marks. First time heterogeneous catalysis has been asked. First time that we have been asked to show something is in excess.First time that I've seen a 5 mark question on rusting iron and been given 3 lines to put it on. It's an absolute disgrace of a paper and some action will have to be taken if the grade boundaries do not reflect it's difficulty. OCR if you are reading this then its not to say go and make F335 easy to make up for your questions. Make it like you do every year, so that those who work hard get what they deserve.

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Spot on. I can't agree more. Absolutely no resemblance to past papers... even the "easy" questions were harder than usual. More application of knowledge than any other paper I've done by a long way. I hope the grade boundaries will be rock bottom but I doubt they'll be that low unfortunately.
7. Tank 2 for Solution a? Tank 1 for B?
8. Why is trypsin preferred over bromate (v)? I put because bromate produces bromine which is toxic and trypsin doesnt get used up so is cost effective. Probably all wrong
9. (Original post by dickbutt)
Yeah I've seen everyone else got 7 too. How did you do it?
99% sure 7 was right @alice
10. The question was 3 marks so I'm pretty sure 3 molecules?! That's what I put anyway
(Original post by Daniel9998)
OH FFSSSS
losing so many marks........................... ..........
11. (Original post by Amyfrancis97)
Is it just me that found this paper ridiculously hard? So frustrating. Anyone else not answer the calculation either?
I couldn't do half the paper! all I wanted was a B calculations were awful :/
12. (Original post by josephinemar25)
I did it the other way round, did the two on the right but could easily be wrong
Can't both options be right? As part of the marks would be for recognising that only one was broken?
13. I was targeting an E in this paper to get a C overall, think that dream is over now though, stuck with my D
14. (Original post by Lozzie97)
BrO3- was in excess, wasn't it? So You had to use the moles of Br- to calculate the moles of Br2 (by dividing by 5 and multiplying by 3). I'm not 100% sure but that is what I did.
Oh crap ur right :'(
15. (Original post by AlbertoMerckx)
Tank 2 for Solution a? Tank 1 for B?
Do you mean tank 1 for Fe ions and tank 2 for Cr ions? Bc thats what i put
16. (Original post by AlbertoMerckx)
Tank 2 for Solution a? Tank 1 for B?
Iron was in tank 1 because it was a positive electrode
17. mandem, what did you man get for 3 marker apparantly bare man are saying zwitterion was formed COS it was neutralised
18. (Original post by yoyo.sat)
Do you mean tank 1 for Fe ions and tank 2 for Cr ions? Bc thats what i put
Yeh!
19. (Original post by yoyo.sat)
Why is trypsin preferred over bromate (v)? I put because bromate produces bromine which is toxic and trypsin doesnt get used up so is cost effective. Probably all wrong
I think this one has to do with trypsin being an enzyme. So advantages associated with enzymes as catalysts.
20. (Original post by B50les)
Can't both options be right? As part of the marks would be for recognising that only one was broken?
it said that the trypsin only breaks that specific amide link so i dont think both would be right

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