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

Guys - does anyone know how to do the last question F324 June 2015? I really can't get my head around it.

Tell me about it!! I have my I S AA tomorrow and its the evluative on identifying 2 weak acids -__- my last attempt to bump my grade up and IDK wth to do pm somebody

Also, I achieved an A at AS, does anybody know what is the lowest grade I can achieve on F326 to still get an A* or an A provided I achieve high marks on the exams??

480 ums to get an A

Lets say you got 240 at AS, and you get A in f324 and f325, tallying up to 240+120+72 = 432

Youd need 40 ums out of 60 for an A in f326, which is like 33 out of 40 (high C)

33 is a b? But thank you

Can someone help with this question please:

A 25.0 cm3 portion of a solution containing Fe2+ and Fe3+ ions was acidified and titrated against potassium permanganate (VII) solution. 15.0 cm3 of a 0.0200 mol dm-3 solution of potassium manganate (VII) were required. A second 25.0cm3 portion was reduced with zinc and titrated against the same manganate solution. This time 19.0cm3 of the oxidant was required.
a) calculate the concentrations of Fe2+ and Fe3+ ions in the solution
b) what percentage of the total iron content of the solution was Fe3+

So far I've done:
MnO4- + 8H+ + 5Fe2+ ---> Mn2+ + 4H2O + 5Fe3+
mole of MnO4 = 3x10-4 mol and mole of Fe2+ = 1.5x10-3 mol (1:5 mole ratio)
concentration of Fe2+ = 0.06 moldm-3

I have no idea how to work out the concentration of Fe3+

I think grade boundaries were 37 for A and 34 for B, i may be mistake, best to be safe and think its higher

Does anyone know how strict examiners when asking for the conditions required for a reaction? (i.e. if I were to write H2SO4 instead of concentrated H2SO4, would I then lose credit?)

Does anyone know how strict examiners when asking for the conditions required for a reaction? (i.e. if I were to write H2SO4 instead of concentrated H2SO4, would I then lose credit?)

I thought they usually say ignore concentrated or dilute but you'd need to say aq for ester hydrolysis? I might be wrong!


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Does anyone know how strict examiners when asking for the conditions required for a reaction? (i.e. if I were to write H2SO4 instead of concentrated H2SO4, would I then lose credit?)

Most of the time it says ignore Ref to Concentration on the mark scheme. Although I have seen times where it says conc but I'm not sure I've ever seen dilute?

So when it asks for reagents I just put concentrated and either way it'll normally be right.

Most of the time they ignore it
I've only seen when it's required for esters and for the reduction of nitrobenzene - pretty sure you must state concentrated H2SO4 and concentrated HCl for those ones

I've worked out the precipitate is Fe(OH)3 but could someone explain how to calculate the gas from density PLEASE

I assume you mean the next question?
Think about the equation to find the volume of a gas: n=v/24,000 cm3
Assume 1cm3 = 1=333x10^-3 g
So that means 24,000cm3 = 1.333x10^-3 x 24,000
That equals 31.992 gmol^-1
On the periodic table the molecular mass closet to this value must be O2 (oxygen) which is 32gmol^-1
So the gas is O2