ocr a f325 revision thread

I thought this paper was definitely challenging; a lot of places to slip up. Definitely much harder than June 12 which was a breeze by comparison. I personally thought Jan13 was more straightforward than this, so my prediction is mid-low 70s for an A, maybe 73? Anyway...

I got NiSO4.7H2O for the formula of the hydrated salt.

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

I completely missed the 4 marker to do with chlorine :/

I got all these!!! :biggrin:

Except the CO2 one :-/

Reply 3561

keepontrying

won't all our rate answers be slightly different because it had to be " after 40 seconds"

Reply 3562

Tania2k9

Original post by TauMuon

I thought this paper was definitely challenging; a lot of places to slip up. Definitely much harder than June 12 which was a breeze by comparison. I personally thought Jan13 was more straightforward than this, so my prediction is mid-low 70s for an A, maybe 73? Anyway...

I got NiSO4.7H2O for the formula of the hydrated salt.

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

I completely missed the 4 marker to do with chlorine :/

I got all that apart from the ferrate ion (i couldn't do) and the i had the ph of bufffer to be 3.57

Reply 3563

Maryb_102

I can't believe i missed out the salt in the last question, had i included the salt, i would have got 7 but i never so i got twelve. FFS.

Reply 3564

amin666

Original post by massi1296

how much was the rate calculation form the graph worth, i didnt draw a tangent just did conc/time (3.4/40) and got 0.085moldm-3s-1

dy/dy=m
the gradian is the rate, i don't remember the numbers

Reply 3565

Little Wing

9

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.

Reply 3566

massi1296

how many marks was the rate calculation form the graph worth? didnt draw a tangent just did 3.4/40 conc/time

Reply 3567

zef1995

10

Original post by keepontrying

I got this too!

Yay

Reply 3568

talliehughes

Original post by jess_m94

I got that for Kc. Can't remember what pH I got but my friend got 3.99. I think I did that one wrong because I'm pretty sure I didn't get it :frown:

I got both 3.99 and put 16.75 for the kc but I don't think they'll be too picky when it comes to rounding numbers

Reply 3569

master y

12

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.

yaay i put something along those lines...

Reply 3570

MathsNerd1

17

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

3 I believe.

Reply 3571

_HabibaH_

8

I think you needed to 'know your stuff', have an IQ of 200, gained a PhD in advanced Maths and Chemistry, won a Nobel Prize in Chemistry and invented the freakin' fuel cell. And even then, maybe it wasn't enough for some of the questions.

Reply 3572

massi1296

i put the h2o breaks down into h+ and oh- in alkali conditions moving the equilibrium to left causing the cell potential to decrease so its lower than the system 6 allowing it to react

Reply 3573

FailedMyExams

8

I was stuck on the last question for so long, figured it out after time ran out, so angry at myself I hope I can get a B at least :frown:

Reply 3574

Benjy100

5

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

Reply 3575

bloomingblossoms

I think this was the hardest yet.. 60 for an A?....

Reply 3576

MathsNerd1

17

Original post by talliehughes

I got both 3.99 and put 16.75 for the kc but I don't think they'll be too picky when it comes to rounding numbers

It's always 3 sf or to the least accurate figure they've provided you with, so you could lose a mark for leaving it as 16.75 :-/

Reply 3577

NerdMeister

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.