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OCR A2 CHEMISTRY F324 and F325- 14th and 22nd June 2016- OFFICIAL THREAD

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Original post by tomlam
idk, I reckon that was the hardest question on the paper though ngl


Nooo that wasn't too bad really.


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Does anyone know how many marks the page on the gold complex was, I ran out of time and didn't answer any of it. Do you think it's still possible to get an A?
Original post by tommason
Does anyone know how many marks the page on the gold complex was, I ran out of time and didn't answer any of it. Do you think it's still possible to get an A?


think it was 6 or 8 marks that single page, im thinking 6
and yeap it should be if everything else was okay
(edited 7 years ago)
No 2015 was easier! I'm with you
Original post by Slenderman
In comparion to 2015. Harder or easier? Am I retarded to think the grade boundaries will be 75 for an A?
Original post by MilkFriend
Anyone got 10.76... no idea about what happened.


It was 20cm3 of 0.0270moldm^-3 NaOH (or whatever?) diluted up to 100cm3, and the Kw was 9.311*10^-14.

New conc = 0.0270/5

So -log(9.311*10^-14 / (0.0270/5)) = 10.76.

I think what the other person may have done is taken it as them adding 100cm3 (I can't remember the question but I think it said diluted up to?) so divided 0.0270/6 and put it in to get 10.68.
Original post by lawlieto
you had to calculate concentrations of acid + base in the buffer solution (that could be 2 marks, each term worth 1 marks)

1 mark for for using the right formula

1 mark for answer?

:biggrin: what have you done in that question?


same as what you do
Original post by ThatPerson2
It was 20cm3 of 0.0270moldm^-3 NaOH (or whatever?) diluted up to 100cm3, and the Kw was 9.311*10^-14.

New conc = 0.0270/5

So -log(9.311*10^-14 / (0.0270/5)) = 10.76.

I think what the other person may have done is taken it as them adding 100cm3 (I can't remember the question but I think it said diluted up to?) so divided 0.0270/6 and put it in to get 10.68.


i did the same ha......:frown:
Original post by lai812matthew
i did the same ha......:frown:


I'm pretty sure it said diluted up to as opposed to added to. I would think that whichever it wasn't would still get most of the marks though.
Original post by ThatPerson2
It was 20cm3 of 0.0270moldm^-3 NaOH (or whatever?) diluted up to 100cm3, and the Kw was 9.311*10^-14.

New conc = 0.0270/5

So -log(9.311*10^-14 / (0.0270/5)) = 10.76.

I think what the other person may have done is taken it as them adding 100cm3 (I can't remember the question but I think it said diluted up to?) so divided 0.0270/6 and put it in to get 10.68.


Ok, thanks, So does that means 10.76 is more likely to be the right answer?
Original post by pezhman
Number of mole of HNO2 was 0.04
Number of mole of NaNO2 was 0.05
0.05-0.04=0.01 [NO2-]
[H+]= (Ka*0.04)/0.01
-log [H+] =pH
I don't remember the Ka


why do you subtract 0.05-0.04? nothing is neutralised
Original post by lai812matthew
same as what you do


i'm confident that's the right thing; there was nothing neutralised; it was simply the case of mixing an acid and it's conjugate base.
Original post by MilkFriend
Ok, thanks, So does that means 10.76 is more likely to be the right answer?


I think so, but I mightve misread it.
Original post by ThatPerson2
I think so, but I mightve misread it.



prerty sue its 10.76 dont worry.
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Original post by lawlieto
why do you subtract 0.05-0.04? nothing is neutralised

No you don't subtact.You just use 0.05 and 0.04.
What percentage of the exam was repeat questions and what percentage of questions needed guessing
(edited 7 years ago)
Original post by Bilal2015
Has anyone done the paper? Unofficial mark scheme?


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What percentage of the exam was repeat questions and what percentage of questions needed guessing
Original post by Slenderman
In comparion to 2015. Harder or easier? Am I retarded to think the grade boundaries will be 75 for an A?

What percentage of the exam was repeat questions and what percentage of questions needed guessing
Original post by Shakikila
What percentage of the exam was repeat questions and what percentage of questions needed guessing


what do u mean by guessing
Any unofficial mark schemes?
Original post by Dinasaurus
I just did this and I expected there to be more to it, the fact she filled the water up to 100.0, had no relevance?


Its because you have the same number of moles in more volume of water because its been diluted so your concentration changes

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