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

1. Hey guys does anyone have the unofficial markscheme for f324? Pleeeeeeaaaassssseeeeeeeeeeee
2. how to tackle those redox titrations at the end????????
3. (Original post by Sab_007)
how to tackle those redox titrations at the end????????
easiest way is to annotate over what it's saying & may draw a diagram to illustrate it better
they'll always be a easy moles calculation in those anyways - no real method but I feel like there won't be a redox titration this year as there were soo many redox questions last year
4. (Original post by Sab_007)
how to tackle those redox titrations at the end????????
do more
5. For electrode potential, in a full cell
Does reduction happen on the positive terminal or negative terminal of the cell?
For example, silver-copper cell
Ag+ + e- = Ag has E= +0.80v
Cu2+ + 2e- = Cu has E = +0.34v
I get that Ag half cell would be going in forward direction and would be the reduction, so in the full cell would the Ag terminal be the positive or negative terminal?
6. (Original post by lai812matthew)
do more
lol i have done loads, still find it confusing tho
7. (Original post by zirak46)
Hello peeps, could someone please explain how in electrochemical cells we decide which half cell is negative electrode and which is positive?

So when drawing a diagram of two half cells, which one goes on left or right?

The question is from Jan 12

Cathode
Positive
Reduction

The equation being reduced is the positive electrode and therefore in an electro-chemical cell the cathode. CPR
8. any help appreciated.... entropy questions!!!!
9. (Original post by VMD100)
Cathode
Positive
Reduction

The equation being reduced is the positive electrode and therefore in an electro-chemical cell the cathode. CPR
I THOUGHT in ELectrochemical cells, it is Cathode OXidation Negative and Reduction Anode Positive!!! :P
10. In electrochemical cells is the negative terminal equivalent to the positive electrode?
11. (Original post by Ss0)
any help appreciated.... entropy questions!!!!
What is the Enthalpy change for that question?
12. (Original post by Ss0)
any help appreciated.... entropy questions!!!!
There are fewer moles of gas in the products so entropy decreases so delta S is negative, so -TdeltaS is positive. The reaction is exothermic so delta H is negative. As temperature increases the magnitude of TdeltaS increases, if the magnitude of TdeltaS is greater than delta H, delta G will be greater than 0 so the reaction will no longer be feasible
13. (Original post by suibster)

Rule: Oxidation= Negative terminal , Reduction=Positive terminal

Identify what's being oxidised and reduced.

O2 is being reduced so ------> Positive terminal

Negative terminal (Al) = -2.31 V
Ahh thanks. I read the question wrong and thought those where the two electrode potentials and didn't realise one was the cell potential.

I like your rule for figuring out which is the positive and negative terminal. Thank you!
14. is everyone expecting a hard paper because f324 was pretty easy? Apparantly their as papers this year were easy too so maybe they'll follow the trend or make this their hardest one yet.
15. (Original post by KB_97)
is everyone expecting a hard paper because f324 was pretty easy? Apparantly their as papers this year were easy too so maybe they'll follow the trend or make this their hardest one yet.
Last year this paper was 87 for an A* and 79 for an A, it was the highest ever...., so yeh I'm definitely expecting a tough one this year
16. (Original post by Ss0)
any help appreciated.... entropy questions!!!!
Assuming the entropy is negative as the number of gas moles decreased.

So Delta G = Delta H - (T x -Delta S)

This makes T delta S positive so

Delta G = Delta H + TDeltaS

As temperature increases, TDeltaS increases, and when TDeltaS>DeltaH.
The Delta G is > 0. Reaction is not feasible if the free energy(Delta G) is bigger than 0.
17. (Original post by megafidget)
Last year this paper was 87 for an A* and 79 for an A, it was the highest ever...., so yeh I'm definitely expecting a tough one this year
Well f***. after the aqa core 3 disaster my only hope for a* is chemistry. It's never gonna happen.
18. Does anyone have a nice way of explaining cathodes and anodes? I keep mixing them up. I know the direction that the electrons flow in but everywhere I look to help explain the terminals, they contradict each other.
19. (Original post by RetroSpectro)
You have to look at this in terms of the Kc expression

Kc = [N2O4] / [NO2]^2

Say we increase pressure by times 2. This means that

Kc = 2 / 2^2
= 2 / 4

Clearly we can see that the bottom of the Kc expression has increased by more than the top. However, the value of Kc cannot change in regards to pressure, therefore the equilibrium shifts right to increase N2O4 and restore the value of Kc.

Hope this helped
20. (Original post by KB_97)
is everyone expecting a hard paper because f324 was pretty easy? Apparantly their as papers this year were easy too so maybe they'll follow the trend or make this their hardest one yet.
I would say from reading many of the conflicting responses about the F324 paper to say it was easy is not entirely true. If anything I believe many here would have scored higher if they sat the 2015 F324 as it had less of the... well... nonsense like the fats and stitches questions. My chem teacher looked at the 2016 F324 and said he would be quite surprised if the grade boundaries changed too much from last year. As far as a pattern I'm not really sure one can be drawn for the F325 grade boundaries.
June 2015: A -79
June 2014: A-74
June 2013: A-75
January 2013: A-70
June 2012: A-76
January 2012: A-77
June 2011: A-72

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