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ocr a f325 revision thread

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Original post by benjy100
i am enraged by ocrs ridiculous wording of the question about finding the rate after 40 seconds. Use the rate equation and the graph?! You only have to use the bloody graph


exactly this!!!!
Original post by Little Wing
the chlorine one was about electrode potentials, in alkali condition the OH- reacts with H+ pushing the position of equilibrium to the left, so more e- are produced in system 7, this reduces the standard potential of the cell making it lower than that of system6.



Did it not shift the equilibrium to the right?
I got FeO4^2- for the ferrate ion (think I missed out the '2-' though :s-smilie:)

I got 3.12 x 10^14 g for the mass of CO2

3.99 for the buffer

13.6 for the alkali pH

4.14 for the weak acid pH

16.8 (think it was no units? Can't remember) for Kc

-3454 kJmol^-1 for lattice enthalpy

got exactly the same!
Original post by slacky123
Did it not shift the equilibrium to the right?


No, H+ was on the left hand side so if you add OH- the system will try to replenish that H+ by shifting the equilibrium to the left.
Original post by Benjy100
I am enraged by OCRs ridiculous wording of the question about finding the rate after 40 seconds. Use the rate equation AND the graph?! YOU ONLY HAVE TO USE THE BLOODY GRAPH


Hahah Ikr! I was like okay, so to work out rate i need to work out k and to work out k i need to work out rate....hang on a minute.... :tongue: I think they just meant so that you don't try and work out the order of water :tongue:
completly messed the complex questions up guessed the equations and put ligand substition for both names
i don't even remember my answers anymore. lol.
Reply 3587
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emah123
OP
5
was is just me or was that the HARDEST PAPER EVER. good bye to medical school :frown::frown:
Original post by massi1296
how many marks was the rate calculation form the graph worth? didnt draw a tangent just did 3.4/40 conc/time


you couldn't of used 40 as your time as it said rate "after" 40s only know this because my chem teacher did a test and there was a similar q on it
NH3 acts as a reducing agent anyone?
Original post by jess_m94
They specifically asked for 3 sf in that question but you'll only lose 1 mark so it's okay :smile:


God damnit! Oh well, usually I always get the kc wrong so I'm chuffed that I've actually done it right for once
Reply 3591
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LRJ
Original post by Brad0440
I put greater, fewer, same...


same, fewer, greater :/
Original post by massi1296
completly messed the complex questions up guessed the equations and put ligand substition for both names


I'm sure 1 was a redox one but the other was a ligand sub so you'll at least get 1 mark
Original post by Benjy100
I am enraged by OCRs ridiculous wording of the question about finding the rate after 40 seconds. Use the rate equation AND the graph?! YOU ONLY HAVE TO USE THE BLOODY GRAPH


Impressive terminology - enraged! I like it.

I'm livid. I don't have the energy for that actually...I'm just disheartened.
Reply 3594
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Yemiisii
Original post by massi1296
completly messed the complex questions up guessed the equations and put ligand substition for both names


I did exactly the same thing :frown:
Reply 3595
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Obtas
12
Original post by emah123
was is just me or was that the HARDEST PAPER EVER. good bye to medical school :frown::frown:


I Feel u bro :frown:
Original post by emah123
was is just me or was that the HARDEST PAPER EVER. good bye to medical school :frown::frown:


I know how you feel lol, I'm saying goodbye to medschool also.
Original post by MathsNerd1
I got all this so hopefully it's all correct! :biggrin:


If I remember correctly I believe I got 16.8 and 3.99 too :smile:
That was an awful exam. Full stop
Original post by Benjy100
Right I'm going to throw some equations at you all

Al + 3CH3COOH ----> Al(CH3COOH)3 + 3H2

2Al +3H+ -----> 2Al3+ + H2

6H+ + 5Sn2+ + 2IO3- -----> I2 +5Sn4+ +6OH-

For the last equation there I should have really used water on the right but they may still allow it

oh its al3+ i used al2+ but did the same thing

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