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

But you still have to apply that knowledge and it is there to catch people out (which it has done)

Not 100% on this, but I imagine the equilibrium lying to the left is related to the attractions between water and I2 not being strong therefore it is not favourable for for I2 to be dissolved.. The equilibrium position is probably caused by the lack of polarity and hence solubility, rather than the solubility being determined by the equilibrium position ygm?

Reply 3321

LThomas694

2

Original post by swetu1

I hated that question soo much... I wrote the equation for the reaction of agno3 and I- and so it gives you agi.. so the con on I- decrease so eq 2 shifts to left and this means more i2 so eq for 1 shifts to left to.. I think I got that wrong.. a total guess

At least we're not the only ones eh, yeah that's what I was thinking but I can't remember if I wrote it down or not? I feel like I didn't have time to write it down which is annoying but that was the only one I left blank so hopefully it will be alright. I think that paper was definitely harder than 2015 and probably 2014 too

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Reply 3322

suibster

3

Original post by Kingofcastle01

Planar?

the shape is linear

Reply 3323

Zaydgt

Original post by douglasaa

Indicator was starch solution, colour change from brown to blue/black

starch solution but from blue/black to pale yellow. it wanted the titration colour change

Prediction for A*?

Original post by swetu1

I hated that question soo much... I wrote the equation for the reaction of agno3 and I- and so it gives you agi.. so the con on I- decrease so eq 2 shifts to left and this means more i2 so eq for 1 shifts to left to.. I think I got that wrong.. a total guess

That's what I got but it seemed so far fetched lol. Hence I said you'd observe more solid being formed.

Reply 3326

k.russell

13

Original post by CaoimheMee

did anyone get 11.73 for ph of dilute NaOH?

20cm^3 of 0.0270mol dm^3 NaOH diluted and made up to 100cm^3
mole of Naoh= 5.4x10^-4
concenctration of NaOH in 100cm^3 = 5.4x10^-3
POH=2.267
so pH= 11.73

Slightly different method, but the same answer! Confident in that one because I did check it twice and and I've done quite a lot of those questions ( I used the value of Kw at 60'C)

Reply 3327

ToLiveInADream

17

I said sodium thiosulfate yellow to colourless but it's starch.

Alsooo the reaction was 2Cu+ +4I- -> Cu2I2 + I2 from aqueous to solid

Reply 3328

mosheezie

1

Piss easy FULL UMS FOR ME! My whole college said it was easy af, you guys stop stressing!
Grade boundaries
A* -90
A - 85
Everything below mehh......

Reply 3329

username1271026

3

was was the enthalpy of hydration question?

Reply 3330

safhassan

3

The paper was quite dodgy. Not as hard as I expected though. And what's with the AS question, such as the shape the solubility of Iodine and the AgI question. Grade Boundaries will definitely be lower than last year.

Reply 3331

Ecconomist

11

Original post by HJS14

Prediction for A*?

Bit harder than last year, 84.

Reply 3332

eeektoe

2

What did you have to do for the last question. All i did was 2.226g/16 and left it at that. Doubt that was right anyway :'(

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Reply 3333

bj1

15

Original post by suibster

the shape is linear

Phew! Had to spend about a minute digging that one up from AS memory...

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Reply 3334

alu4days

1

Original post by CaoimheMee

did anyone get 11.73 for ph of dilute NaOH?

20cm^3 of 0.0270mol dm^3 NaOH diluted and made up to 100cm^3
mole of Naoh= 5.4x10^-4
concenctration of NaOH in 100cm^3 = 5.4x10^-3
POH=2.267
so pH= 11.73

Hey were you supposed to use 100cm3 or 120cm3?
Because if its diluted you should take the total volume of everything?

Reply 3335

ToLiveInADream

17

Original post by bj1

How would you know it's yellow? I just said 'forms a precipitate'. I wrote out the relevant equations rather than saying eqb shifts 'left/right"

Not sure why I got 4.5 at the end for X, my method and numbers beforehand seem to be the same as others, perhaps I rounded too early? Or used incorrect Mr?

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F321 - yellow precipiate formed from Ag + I

Reply 3336

screwedmofo

1

Original post by CaoimheMee

did anyone get 11.73 for ph of dilute NaOH?

20cm^3 of 0.0270mol dm^3 NaOH diluted and made up to 100cm^3
mole of Naoh= 5.4x10^-4
concenctration of NaOH in 100cm^3 = 5.4x10^-3
POH=2.267
so pH= 11.73

i got 11.72, what did u get for the ph of the buffer of HNO2 i got 2.12?

Reply 3337

NervousBoy

4

Anyone get 2.9x10-2 for the Kc value of the order's question because it said apportriate significant figures and standard form?

Reply 3338

username2640523

8

Original post by CaoimheMee

did anyone get 11.73 for ph of dilute NaOH?

20cm^3 of 0.0270mol dm^3 NaOH diluted and made up to 100cm^3
mole of Naoh= 5.4x10^-4
concenctration of NaOH in 100cm^3 = 5.4x10^-3
POH=2.267
so pH= 11.73

It was at 60 degrees C not 25, you dont use 25 degrees C Kw which is 10^-14, you use the one it gave in the question as it said 60 degrees.Think the answer was 10.76

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(edited 7 years ago)

Reply 3339

k.russell

13

Original post by LThomas694

At least we're not the only ones eh, yeah that's what I was thinking but I can't remember if I wrote it down or not? I feel like I didn't have time to write it down which is annoying but that was the only one I left blank so hopefully it will be alright. I think that paper was definitely harder than 2015 and probably 2014 too

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I put the same stuff with reference to the equilibria, then I was talking about how you would see a mixture of yellow and grey-black precipitates? AgI is yellow and it says I2(s) is grey-black

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

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