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Aqa chem 4/ chem 5 june 2016 thread

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Original post by irendeep
Im not refering to delta H im refering to delta S.


Sorry, I misread

But still, it is the exact same argument. That question asks for the 'entropy change of the formation of....'

It's still referring to formation here. So the same argument applies.
Can someone help me out with a few Qs- for the one about environment , can you just put h20 only product or do you have to hammer on about it not being as bad as co2? Also on the Q (7 marks) about adding ethanediol te to co2+ do you have to say delta H is the same ?:/ also the very last Q - can you say: mn04- absorb white light frequencies and the freq not absorbed detected by colouring ter to give value of conc
very similar to last years paper in terms of difficulty, slightly easier.

A*: 86
cap: 93/94
Original post by slb971
For the final part of Chromium question with excess OH-, would [Cr(H2O)2(OH)4]- be acceptable or not? I remember seeing a couple textbooks had this instead of [CR(OH)6]3-


That would be fine, along with [Cr(H2O)(OH)5]2-

:smile:
Original post by Fibsy
Can grade boundaries for A* possibly be higher than 89?

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Original post by ravichauhan11
very similar to last years paper in terms of difficulty, slightly easier.

A*: 86
cap: 93/94


I agree with these (second quote)
My guess for what I think I got on this paper is about 68. How close do you think this would be to the A boundary?

Thanks :smile: Best of luck to you all

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Original post by Suits101
No to first
Yes to second


Why would excess conc. NH3 not be accepted though - surely that just makes [Cr(NH3)6]3+ which is a green solution?
Still don't get why increasing the pressure of the oxygen would make a difference... surely they're not all gaseous so it wouldn't make a difference?
Original post by Aethrell
Still don't get why increasing the pressure of the oxygen would make a difference... surely they're not all gaseous so it wouldn't make a difference?


I Think it was H2 gas that was a gas ?
Original post by Sloth45
Why would excess conc. NH3 not be accepted though - surely that just makes [Cr(NH3)6]3+ which is a green solution?


Thats what I thought, and ultimately put down. Some people seem to say that [Cr(NH3)6]3+ is purple, though. It's possible that the mark scheme would allow it? I'm not sure, should have just stuck with NaOH :frown:
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Original post by Sloth45
Why would excess conc. NH3 not be accepted though - surely that just makes [Cr(NH3)6]3+ which is a green solution?


That's purple not green, but mark schemes tend to have a long list of accepted colours so green might be one of them who knows. You could check mark schemes of similar questions.

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(edited 7 years ago)
How many marks for 51% on last question?
For the purity question I put 2 answers, ones right and the other is wrong. Would they take away marks for having 2 answers even if one is right?
Original post by Sloth45
Why would excess conc. NH3 not be accepted though - surely that just makes [Cr(NH3)6]3+ which is a green solution?


Original post by Shadazar
Thats what I thought, and ultimately put down. Some people seem to say that [Cr(NH3)6]3+ is purple, though. It's possible that the mark scheme would allow it? I'm not sure, should have just stuck with NaOH :frown:


No it's a purple solution. Plus that's saying NH3 with [Cr(H20)6]3+ produces CO2 gas from reaction 3 or whatever it was.

Sorry.
Original post by Suits101
No it's a purple solution. Plus that's saying NH3 with [Cr(H20)6]3+ produces CO2 gas from reaction 3 or whatever it was.

Sorry.


Yeah Im pretty sure it will be accepted tbh, in the past when theyve asked what colour the ammonium ion is theyve accepted green so i think we'd be unlucky not to get the marks :smile:

And mate we're not saying that, we're talking about the reaction of NH3 with Cr(oh)3(h2o)3 which wouldnt give CO2 idk what youre on about

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Guys was the weakest oxidising agent Zn or Zn2+
Can someone please explain thr tick box one? I ticked H2SO4 as HCl and H2C2O4 would interfere but i dont see why HNO3 wouldn't work?
Original post by Aerosmith
Guys was the weakest oxidising agent Zn or Zn2+

Zn2+
Original post by Sloth45
Yeah Im pretty sure it will be accepted tbh, in the past when theyve asked what colour the ammonium ion is theyve accepted green so i think we'd be unlucky not to get the marks :smile:

And mate we're not saying that, we're talking about the reaction of NH3 with Cr(oh)3(h2o)3 which wouldnt give CO2 idk what youre on about

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The reaction was for a green solution from Cr(H2O)3(OH)3 and I've never seen [Cr(NH3)6]3+ being accepted (hence reagent being NH3 in excess) because this is a purple solution, only [Cr(OH)6]3- is the green solution from Cr(H2O)3(OH)3 with excess NaOH I've seen accepted?

Original post by Aerosmith
Guys was the weakest oxidising agent Zn or Zn2+


Zn2+
Original post by IvoryToast
Can someone please explain thr tick box one? I ticked H2SO4 as HCl and H2C2O4 would interfere but i dont see why HNO3 wouldn't work?


The HNO3 is an oxidising agent so it would also interfere, meaning you get a lower amount of MnO4 used in the titration

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