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

Nope
http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/electrode.html

This diagram is clearer

The reactions we are doing generate electrical energy, not require it.

In accordance to electrode potentials, the one with the highest electrode potential is forward. The one with the more negative electrode potential has the reverse reaction, balance and add together and remove electrons.

https://gyazo.com/49069f767bf5ea95d7e870c6a979a5e2 How do we know that 2 mol X reacts with 2 mol Cr? 1.456/1.021 = 1.43, do we just round 1.43 up to 1.5? seems a bit off :/

No, 2 moles of X reacts with 3 moles of Cr I believe. If you write out the half equations you get this ratio:

Cr3+ + 3e- --> Cr (we know it gains 3 electrons because it says chromium(III))

X --> X2+ + 2e- (X is losing mass, so it must be forming X2+ aqueous ions)

The ratio of electrons in each equation is 3 (Cr) : 2 (X)

The no. of moles of Cr is 0.028 mol, so divide that by 1.5 (3/2) to get no. of moles of X.

Then work out the Mr which is 54.6 g mol-1 and this essentially has same atomic mass as manganese. (54.9)
This is how I worked it out and it got me the right answer

Nope
http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/electrode.html

This diagram is clearer

The reactions we are doing generate electrical energy, not require it.

F325 will be impossible. I'm calling it. F324 was freakishly easy, and they can't make F325 easy again or too many people will get an A*. Prepare your anus lads and lasses.

but I- E potential is lower than Fe, so surely that means Fe3+ would react with I- and not Fe2+? cofused

I'm confused so which one do we do?? So is cathode positive or not

Oh you meant equation 2 and the reaction with Fe3+ going forward is higher so it goes forward, as 0.77 > 0.54.

The 2I- forward equation is lower as 0.54<0.77, so you have to reverse it so 2I- reacts with Fe3+

too many people can't get A*'s there's always a set amount who do get A*s, it doesn't increase just because a paper is easy. It doesn't work that way

F325 will be impossible. I'm calling it. F324 was freakishly easy, and they can't make F325 easy again or too many people will get an A*. Prepare your anus lads and lasses.

Ohh thanks so much

(typo in my initial question, meant 2mol X with 3mol Cr)

i just hope there are no long word questions, only calculations and equations

I didn't realise you are hoping to study chemistry at uni and you made Bath your insurance! I'm hoping to study chemistry also, but I've made Bath my firm!

Uhmm, I have nothing to say other than you're severely misinformed? Not sure who told you this.

http://www.bstubbs.co.uk/a-lev.htm

doesn't look constant to me? That definitely isn't a set amount...

I'm confused so which one do we do?? So is cathode positive or not

yep, i really liked Bath need A*AA for my firm so Bath is quite likely tbh

what I mean is, it is within a range which is kept fairly constant

100 marks of pure calculations and equations is wishful thinking dont you think? haha.