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Aqa chem 4/ chem 5 june 2016 thread

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Original post by shiney101
This was a dodgy question, I guess it as r=k[I2][H+], what did you put down?


I wrote exactly the same as the one they gave us.

k is constant (as temperature is not varied) and I2 is not involved in the rate-determining step so it cannot appear in the rate equation.

The only things that could affect the rate are concentrations of propanone and protons, which would change.
Original post by Ljm1998
Aqa set their A*'s at 90% UMS, and after that the grade boundaries for an A are the total pupils scored below A* and find the 10% then again for BCand D, yet I will make a petition, where should I put it? Change.org? Or Facebook?


Both :biggrin:
Original post by ishabennett
Literally same

That's exactly how I feel - thought I was on track for an A* but defo not after this
Original post by Ljm1998
Aqa set their A*'s at 90% UMS, and after that the grade boundaries for an A are the total pupils scored below A* and find the 10% then again for BCand D, yet I will make a petition, where should I put it? Change.org? Or Facebook?


Both, but change.org for sure!
Original post by Cadherin
I wrote exactly the same as the one they gave us.

k is constant (as temperature is not varied) and I2 is not involved in the rate-determining step so it cannot appear in the rate equation.

The only things that could affect the rate are concentrations of propanone and protons, which would change.


Original post by NobodyCares
I put the same as you - it was either that or r=k[H+], but i put that I2 was not in the rate equation before because it was in excess (guessing), so as it is not in excess I put it in


Original post by shiney101
This was a dodgy question, I guess it as r=k[I2][H+], what did you put down?


I agree the question was dodgy because it didn't state I2 wasn't in RDS, it just asked you to suggest why. It could have been that I2 was in massive excess in which case it would appear to be pseudo order. This was a very tricky question I thin.... I think it's safe to say propanone was pseudo order, so would appear to be zero order, but they may still include in rate equation? In which case it'd just be the same? However I think this would be very strange of AQA... I went with r=k[h+] in the end using the logic I2 not in rds and the ketone is in massive excess so won't affect the rate... Hopefully this is right!
Reply 1405
Original post by House6797
Using AgNO3 is the answer AQA were probably looking for
however i wrote the same as you and im 99% we are right


Is this for the acyl chloride and the ketone? I put silver nitrate too, but now I realise that there was a chlorine on both of them so silver nitrate would produce a white ppt with both :/

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i got 22 hydrogens but thought the total mass was 220? ended up with 10% as answer
Original post by chem4wasshit
i got 22 hydrogens but thought the total mass was 220? ended up with 10% as answer

I definitely didn't get exactly 10% - I think i got 9.? - not saying you're wrong though
I got 23/233 :frown:
Original post by Cadherin
I got the empirical formula then multiplied this by the ratio of (Mr of molecular ion/Mr of empirical formula) which was equal to 2.


Will you get marks for this way??
tests for acyl chloride- can you use sodium hydrogen carbonate?
Original post by zombaldia
I agree the question was dodgy because it didn't state I2 wasn't in RDS, it just asked you to suggest why. It could have been that I2 was in massive excess in which case it would appear to be pseudo order. This was a very tricky question I thin.... I think it's safe to say propanone was pseudo order, so would appear to be zero order, but they may still include in rate equation? In which case it'd just be the same? However I think this would be very strange of AQA... I went with r=k[h+] in the end using the logic I2 not in rds and the ketone is in massive excess so won't affect the rate... Hopefully this is right!


It may be possible that they allow more than one answer (but not one with iodine) I would have thought. If lots of candidates offer alternatives (which is possible) and as long as you justify it properly, this may be the case.

Or M1 may be dependent on a properly explained M2.
Original post by TJ_gym
Will you get marks for this way??


I can't see why not - it's the most valid method I've seen so far.

Besides, it was a unit 1 synoptic question and I think AQA were hinting at that by the way they asked the question.
Original post by Medlad101
lidocaine is basic so adding hydrogen chloride would make it a neutral pH so that it wouldnt harm the patient, thats what i put


Omg that's what I put too! Literally thought I was the only one,I mentioned it not being too strong a base so it doesn't denture your enzymes
(edited 7 years ago)
Original post by Cadherin
It may be possible that they allow more than one answer (but not one with iodine) I would have thought. If lots of candidates offer alternatives (which is possible) and as long as you justify it properly, this may be the case.

Or M1 may be dependent on a properly explained M2.


I agree, seems logical they will award M1 based on reasoning of M2
Reply 1415
For the Cl containing ketone and acyl chloride test, although both have a Cl so you would think both would form a white ppt with silver nitrate... is the haloalkane reactive enough to release the Cl?
Do you not have to release the halide first with aqueous NaOH for that to happen?

... just me trying to defend my pitiful case for 3 more marks

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Original post by zombaldia
I agree, seems logical they will award M1 based on reasoning of M2


Mind you, I think I had a VERY lucky guess of the last compound on the 9 mark analysis, as I wrote down as much info as I could and sort of half-guessed it with 30 seconds left.
Original post by emilies18
tests for acyl chloride- can you use sodium hydrogen carbonate?


Yh you can
i think this is the answer for the last question
Could we say that i2 wasnt included as it was a solid?

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