For redox questions:

Weakest OA: Zn2+
Conventional cell diagram: Zn | Zn2+ || Co2+ | Co
Half equation: Zn -> Zn2+ + 2e-
Cobalt species: Co3+, oxidation product is oxygen, then reaction

Negative electrode: H2 + 2OH- -> 2H2O + 2e-
Positive electrode: 4e- + O2 + 2H2O -> 4OH-
Overall reaction: 2H2 + O2 -> 2H2O
Graph of emf: just a straight horizontal line

Isn't the positive and negative electrodes the wrong way around?

Reply 2524

ravichauhan11

Original post by randoms132

No - the starting reactant was [Co(H2O)6]2+ and the product was [Co(h2nch2ch2nh2)3]2+ not same type of bonds are broken as are formed but same number yes

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same question came up in 2014, mark scheme : " Allow same number and type of bonds broken andformed"

Reply 2525

Matt Johnson

Original post by Pippy12345

Did it ask for examples?

No, just said state 3 characteristics

Reply 2526

K2Cr2O7

Original post by Pippy12345

What did everyone get for the characteristics of chromium chemistry question?

Formation of complex ions
Coloured ions
Variable oxidation states

Reply 2527

sk123456

Original post by idk97

Why is the purity 94 and not 50.7???/

I too got 50.7 but apparently its wrong

Reply 2528

DDan123

Original post by Hopefulmedic15

I sat last years paper and this year's and I think they're about the same in difficulty although the calculation on this year's may have tripped up more people so I think the grade boundaries will be about the same if not one ums less for each grade boundary compared to last year

I think after chem 4 a lot of people have just found this paper a lot easier in comparison. But I agree. It wasn't an extremely easy paper, but not insanely difficult.

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Reply 2529

Pippy12345

Original post by randoms132

No it didnt :-)

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Ok phew!

Reply 2530

GO97

Original post by randoms132

Straight horizontal line?

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crap i put it would increase first then stay constant

Reply 2531

randoms132

Original post by ravichauhan11

same question came up in 2014, mark scheme : " Allow same number and type of bonds broken andformed"

But that was from a reactant of [Co(NH3)6]2+

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Reply 2532

Kay Fearn

Damn lost two marks on the alkaline fuel cell question, couldn't work it out in time.

Also got 35.2% for the % purity question but that's % by mass so think i lost like 4 marks from both of those^^

i said increase in pressure increases emf because when more oh- formed/reaction speeds up not sure if that's right tho :/

For the last 3 marks what did people say? I talked about mixing two solutions indifferent proportions one containing ligand and one containing mn04- then shine light through a filter at the solution and use data logger to measure absorbance then find ratio at max absorbance.

Reply 2533

Pippy12345

Original post by sk123456

I too got 50.7 but apparently its wrong

I also got 50.7 and so did quite a few others at my school

Reply 2534

minjinoor

Original post by SirRaza97

That was the nicest paper in the god damn world. Apart from the 7 marker calculation question it was so easy. Definite A*

what do you think grade boundaries will be?????

Reply 2535

Suits101

Original post by randoms132

No - the starting reactant was [Co(H2O)6]2+ and the product was [Co(h2nch2ch2nh2)3]2+ not same type of bonds are broken as are formed but same number yes

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