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Aqa chem 4/ chem 5 june 2016 thread

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Can someone please explain to me why the emf would increase if pressure of oxygen increases? Thanks! :smile:
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Anam
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Original post by Suits101
Multiply atomisation and ionisation enthalpies of K by 2


I only multipled the 90 by 2 how many marks lost? :frown:
Original post by Anam
I only multipled the 90 by 2 how many marks lost? :frown:


It was only 2 marks.

Maybe both? One if you're lucky because cycle was given.
Reply 2883
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Anam
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Why a small pellet of vanadium used?
Is there an unofficial mark scheme anywhere?
increase the surface area
then impurities poison the catalyst for 2 marks 2 differetn questions
Original post by FireBLue97
You know what I think there was another one of AQAs infamous typos the question was supposed to say standard enthalpy and instead they put enthalpy by accident so it means that this question will probably be free marks for everyone who has either put the 135 or the 62.5 hopefully


this definitely won't be the case as the question clearly implied to use the full reaction instead of 1 mole produced. Also, AQA never give out free marks lol.
Original post by chloeabeki
Would I lose marks for not having my coordinate bonds as arrows? I drew them like normal covalent bonds and now I'm kicking myself!


**** i did the same
Canu put nh3 as the reagent to form R in the chromium question?
I did R as Cr (oh)4 - so i was wondering
return of the potato cell so what are ur thoughts dividing by 2 or not dividing by 2
For the complex that we had to draw I used arrows instead of lines is that okay?
Original post by SuruthiG
Canu put nh3 as the reagent to form R in the chromium question?
I did R as Cr (oh)4 - so i was wondering


I did that! I'm kicking myself for not thinking of CO2. Maybe its still right?
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Anam
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Original post by SuruthiG
Canu put nh3 as the reagent to form R in the chromium question?
I did R as Cr (oh)4 - so i was wondering


I put R as [cr(oh)6]3- and the reagent as NaOH, NH3 would give [cr(nh3)6]3+ wouldnt it?
Original post by FireBLue97
return of the potato cell so what are ur thoughts dividing by 2 or not dividing by 2


You shouldn't have divided by 2. The answer was -135 or something similar.
Original post by Jonnyss
Standard just means standard conditions tho??
Like pressure and temp.


yeah an enthalpy change does not have to be for one mole, only the case if it's one of the definition ones eg enthalpy of atomisation, that must produce one mole. So I don't see why you'd divide by 2.
Original post by Anam
Why a small pellet of vanadium used?


Original post by FireBLue97
increase the surface area
then impurities poison the catalyst for 2 marks 2 differetn questions


Spot on.

Original post by SuruthiG
Canu put nh3 as the reagent to form R in the chromium question?
I did R as Cr (oh)4 - so i was wondering


Wasn't R Cr(H2O)3(OH)3? If so then yes.

Original post by shiney101
For the complex that we had to draw I used arrows instead of lines is that okay?


That's the proper way to do it :smile:
Original post by Suits101
Was Gibbs free worth 3 marks?

Also can anyone confirm for MgCl2 solubility one:

Solubility decreases
Forward reaction is exothermic
Equilibrium shifts left to oppose increase in temperature


That's what I put!
Original post by Lolaturface
That's what I put!


Woo! :smile:
Original post by Ginpls
Can someone please explain to me why the emf would increase if pressure of oxygen increases? Thanks! :smile:


bumping this up because im wondering the same thing
Original post by Darthsion100
I got something like 2328 KJ Mol-1 at first, then I halved the atomisation of oxygen to get 2404, but I think the original answer of 2328 was correct, because atomisation is for one mole, and you got 1 mole of O


I got 2328!!

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