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# OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012

Chemistry exam discussion - share revision tips in preparation for GCSE, A Level and other chemistry exams and discuss how they went afterwards.

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1. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
hey anyone wants to revise tomorrow chapter 1> ?
2. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by otrivine)
hey anyone wants to revise tomorrow chapter 1> ?
Yeah why not?
3. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by LifeIsGood)
Yeah why not?
shall we do some now?
Ok
ill start
Define:strong acid and give an example (3)
4. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by otrivine)
shall we do some now?
Ok
ill start
Define:strong acid and give an example (3)
A strong acid is an acid which completely dissociates.
Example: HCl
HCl --> H+ + Cl-
5. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
Does anybody know how you know when you need to X1000 or divide by 1000 in the 'Free energy change' calculations? In some questions it asks you to put entropy of reaction in J and others in KJ so i'm not sure which to do
6. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by Silkyy)
Does anybody know how you know when you need to X1000 or divide by 1000 in the 'Free energy change' calculations? In some questions it asks you to put entropy of reaction in J and others in KJ so i'm not sure which to do
Converting from kJ to J: multiply by 1000
Converting from J to kJ: divide by 1000

Think about it this way - there are 1000J in one kJ.

Oh and as long as you are consistent with your units you should get the same answer; if you are specifically asked to change to a particular unit then do so.
Last edited by Killjoy-; 27-05-2012 at 18:12.
7. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by LifeIsGood)
A strong acid is an acid which completely dissociates.
Example: HCl
HCl --> H+ + Cl-
yes excellent my turn
8. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
So should i always convert it into KJ or J?
9. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by Silkyy)
So should i always convert it into KJ or J?
hi can we ask questions on chapter 1?
10. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by Silkyy)
So should i always convert it into KJ or J?
All quantities must have the same prefix, so either all in kilo or all without kilo.
11. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by otrivine)
hi can we ask questions on chapter 1?
I'm afraid that I can't - I'm doing FP3 at the moment.
12. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by Killjoy-)
I'm afraid that I can't - I'm doing FP3 at the moment.
10 min only please only on chap 1
13. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by otrivine)
yes excellent my turn
You Can ask me
If you want
14. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by kingam)
You Can ask me
If you want
sure but you start chap 1
15. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by otrivine)
sure but you start chap 1
Erm , how do work out the ph of a strong base
16. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by kingam)
Erm , how do work out the ph of a strong base
by doing titration and using a PH meter to see how strong the base is from PH 8-14 AND there is a formula to find PH which is PH=-Log(H+)
17. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by otrivine)
by doing titration and using a PH meter to see how strong the base is from PH 8-14 AND there is a formula to find PH which is PH=-Log(H+)
Erm not really you subtract 14 from - log oh value .
18. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by kingam)
Erm not really you subtract 14 from - log oh value .
oh so would i get no marks?
ok
how can you check change colour (2)
19. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by otrivine)
oh so would i get no marks?
ok
how can you check change colour (2)
Your probably wouldn't as they are like calculation questions , and colour change you choose an indicator and one colour appears in its conjugate base and acid , for eg methyl orange can change from red to yellow , is that t question was a
Bit vague lol
20. Re: OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012
(Original post by kingam)
Your probably wouldn't as they are like calculation questions , and colour change you choose an indicator and one colour appears in its conjugate base and acid , for eg methyl orange can change from red to yellow , is that t question was a
Bit vague lol
No you would do a precepitation reaction
but yes you seem to get the point
ok my turn

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