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# AQA Chemistry Unit 4 January 2010 (new spec) watch

1. i could not of asked for a better paper..
2. (Original post by antony492)
Yh i did. And then i added CN. But i didnt know where to go from there. But at least i got some of the marks.

I wish people didnt find this easy, it means that they wont put the grade boundaries down.
Then H2 and Ni to hydrogenate
3. Ok then, so if i remember correctly there was 0.001 moles of NaOH added to 0.01025 of ethanoic acid - lets call it HA. (these were calculated from the given volumes and concentration of solutions)

So then the NaOH reacts with the HA so that there is now 0.01025 - 0.001 = 0.00925 moles of HA, and 0.001 moles of A'.

Then input these values into the Ka equation so that [H]= Ka x HA / A'.

The volume of the solution (35cm^3) cancels out i believe (or wrongly believed).

and when i put the concentration of H+ into the pH formula i got 3.79.

I apologise if this is wrong, and would be grateful if someone could point me in the right direction.
4. (Original post by Funkachillislap)
sweeet. Then i got 3.79 for the pH of the buffer solution but only one of my friends got that answer - we're both pretty sure though.
if anyone fancies iit i can talk through my method of the question cos i still remember it.
I got 3.79
5. (Original post by Funkachillislap)
Ok then, so if i remember correctly there was 0.001 moles of NaOH added to 0.01025 of ethanoic acid - lets call it HA.

So then the NaOH reacts with the HA so that there is now 0.01025 - 0.001 = 0.00925 moles of HA, and 0.001 moles of A'.

Then input these values into the Ka equation so that [H]= Ka x [HA] / [A'].

The volume of the solution (35cm^3) cancels out i believe (or wrongly believed).

and when i put the concentration of H+ into the pH formula i got 3.79.

I apologise if this is wrong, and would be grateful if someone could point me in the right direction.
I agree with 0.001 KOH, therefore 0.001 [OH-]
But as ethanoic isn't a strong acid only a tiny fraction of H+ is formed, so [H+] is worked out using the n(H+) (in 1 mole of ethanoic acid) from the previous question divided by the volume (0.035dm3) giving a verrrry small answer of around 0.00006677. So [OH-] is greatly in excess and i got ph to be about 12.
Makes sense if you think of Strong base into a weak acid..

http://www.thestudentroom.co.uk/show...122608&page=51
7. It was 3.79. Doesnt matte how strong the base is if only a little is added
8. Argh...I didn't like this paper so much, I spent alot of time revising through NMR and structural determination and am actually quite disappointed they didn't give us a graph for a question.

Can anyone get hold of the paper and go through the solutions?
9. so there were two Ka questions

i got 4.80 for the shorter one which was worth 3-4 marks
and then 3.xx (cant rmb) for the next longer one

im pretty sure its not 12 for the longer 6 mark question
according to textbook p47 example 2 the alkali is used up, very similar to what we did this morning
10. i totally over thought that qu... all the base would be used up because the equ would keep being re-established for the HA, thus providing as much H+ as required... my bad
11. what was optically active answer?
12. Reduction of Y to diamine: Needs 12[H] in the equation? Sn/HCl reagents?
Combustion of the ester: Needs 21.5 O2 to make 15 CO2 and 15 H20?
Drawing the curly arrows on: one from C-H bond to C, one from C-C+ bond to C+ ?

--

For the pairs of structures:

First one was A) ketone on the middle of three carbons and B) C=C with two Hs on one side and a CH3 and an OH on the other.

Ester one was one with 3/1 carbons and one with 2/2 carbons. (/ is the COO)

Amine one was the 2 peaks for C-C-N-C-C and three peaks for C-N-C-(2 CH3s from that C)

Tollens one was one with a C(CH3)3-CO-CH3 for the ketone and C(CH3)3-CH2-CHO for the aldehyde.

C5H12 one was one pentane and one C with 4 CH3 groups on it.

--

Also, how many marks would I lose for not remembering that H2SO4 is diprotic? One in the pH part and two in the NaOH moles calculation part?
13. I thought this exam was pretty nice

Ill find out come results day though!
14. Hey, thought it was good, but after seeing discussed answers i feel panicky haha,
with the last question someone said about the synthesis of CH3Cl, i just did nuclear substitution of CH4 with HCL, that does work but i hear some of you have talked about free-radical substitution, so which one is it !!! :P
15. (Original post by Funkachillislap)
sweeet. Then i got 3.79 for the pH of the buffer solution but only one of my friends got that answer - we're both pretty sure though.
if anyone fancies iit i can talk through my method of the question cos i still remember it.
Same I'm pretty confident that that was the right answer, although I only got it when I checked as initially i forgot to minus the OH- from the ethanoic, so i got 3.71 or something.

16. I got 4.something for the buffer question
oh well
17. glad you guys liked the AQA one....ocr was pretty damn hard
18. (Original post by Get Cape.Wear Cape.Fly.)

http://www.thestudentroom.co.uk/show...122608&page=51
19. Why can't you resit??

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