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

For the equilibrium question I put: I- reacts with Ag to form agI (yellow ppt), therefore the position of equilibrium will shift to the left to restore I- conc. As a result, more aqueous iodine was formed so the position of equilibrium of 1 will also shift to the left, therefore more grey/black solid iodine is formed. For the electrochemistry question I needed up with two equations. The oxidising agent one where Cr+3 reacts with AL and the reducing agent one where Cr+3 reacts with feO4- or something. Anyone else?

for the cr+3 to cr2o7 part - I thought that as they only gave you cr3+ the reaction had to backwards - so you could pretty much switch the sign on the ev - and that gave me two equations - I don't exactly remember what. I'm really quite unsure whether that was a correct assumption.

Reply 3461

dairychocolate

11

Original post by cr7alwayz

For using a calculation to explain why K2SO4 can dissolve at 25oC was the entropy change 0.02 or something which is positive so the reaction is feasible?

G was negative so the reaction was feasible.

Reply 3462

cr7alwayz

8

For the very first question did people get Cu(H20)2(NH3)4 or Cu(nh3)4. I put the first one with deep blue as the colour becuase I didnt know what the colour of Cu(NH3)4 was.

Reply 3463

MrZebraCookie

2

Does anyone have a copy of the paper?

Reply 3464

username2640523

8

Original post by cr7alwayz

For using a calculation to explain why K2SO4 can dissolve at 25oC was the entropy change 0.02 or something which is positive so the reaction is feasible?

Temp was 298K you get negative 43 or something so its feasible as delta g is neg

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Reply 3465

bridget07

How many marks was the AgNO3 equilibrium shift?

Reply 3466

Professor L

14

Original post by lai812matthew

what the f is a standard form??????????

(something between 1 to 10) times 10^(something)

Can't remember the exact answer, but 0.029 in standard form would be 2.9 x 10^(-2)

Reply 3467

Serine Soul

18

Original post by maisym00

For the equilibrium question I put: I- reacts with Ag to form agI (yellow ppt), therefore the position of equilibrium will shift to the left to restore I- conc. As a result, more aqueous iodine was formed so the position of equilibrium of 1 will also shift to the left, therefore more grey/black solid iodine is formed. For the electrochemistry question I needed up with two equations. The oxidising agent one where Cr+3 reacts with AL and the reducing agent one where Cr+3 reacts with feO4- or something. Anyone else?

Exactly what I did!

Original post by EricPiphany

Don't worry you'll be fine.

Speaking to people who sat the exam with me, lots of them messed up the buffer question.

I certainly messed up parts. But with high UMS last year, and good UMS in the first exam, I should have the A I need.

Yeah, hopefully A* boundary is low and I'm safely into it. I'm really counting on chem to be one of the 2A* in need to make my offer :redface:

Reply 3468

Randall13

8

What did people get for the empirical formula one?

I got the fact it was the same as the molecular formula but not 100% on it.

Reply 3469

Brandoncarlin

1

Original post by postexamtalk

H2O2 + I- forms HIO + OH-
H+ + OH- forms H2O
HIO + H+ forms I2 + OH- (given)
H+ + OH- forms H2O

Both valid?

Need 2I- on the left-hand side

Reply 3470

medstudent1010

4

Original post by k.russell

For the question about acidic or alkaline at 60'C with a pH of 7, did no one use 10^-7 = [H+]? Because that statement has to true by definition doesn't it? So I then divided the Kw at 60'C, (which was 9.4 blah blah x 10^-14) by 10^-7, giving 9.4 blah blah x 10^-7 for [OH-] then I said that [H+] > [OH-] so the solution is acidic. Sorry to go against the flow, but my method makes complete sense to me and I think it's right, if anyone can show me why that's wrong, please go ahead (or if you think I'm talking sense please back me up lol)

Your method is right however your conclusion is wrong 9.4x10^-7 >1x10^-7 hence solution is alkali

Reply 3471

mamounaltayeb

I got that one too

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Reply 3472

Jm098

2

It said leave the answer in standard form

Reply 3473

milemed11

1

Original post by bridget07

How many marks was the AgNO3 equilibrium shift?

4 marks

Reply 3474

username2640523

8

Original post by Randall13

What did people get for the empirical formula one?

I got the fact it was the same as the molecular formula but not 100% on it.

There was one Cu so it was the molecular.
anyway I got CuO8H4C4 with 2- charge?

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Reply 3475

Beta14

1

Yh i got that too

Original post by Randall13

What did people get for the empirical formula one?

I got the fact it was the same as the molecular formula but not 100% on it.

Reply 3476

maisym00

8

Pretty sure the reagent was starch and the observation was blue/black to colourless. You can type it into YouTube and see the end point; and that's what happened