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OCR Chemistry A Exam Thread (Breadth - May 27 2016 and Depth - June 10 2016)

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Original post by Internets
With electronegativity questions, would it be better I wrote about the specific dipole-dipole interactions or just say van der Waals' or London forces?

Also, just to clarify, are van der Waals' referring to induced and permanent and London only induced?


I wouldn't say van der Waals. I don't think they want that anymore. Instead refer to either london forces, permanent dipoles and hydrogen bonding
Reply 641
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aj2152
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Original post by Internets
With electronegativity questions, would it be better I wrote about the specific dipole-dipole interactions or just say van der Waals' or London forces?

Also, just to clarify, are van der Waals' referring to induced and permanent and London only induced?


Generally the mark scheme will say allow van der Waals when talking about London forces. I think it's because on the old spec they mentioned that van der Waals is induced dipole dipole interaction (London forces) and this year they changed the name but some people are retaking so the van der Waals is still acceptable
Original post by 4nonymous
I wouldn't say van der Waals. I don't think they want that anymore. Instead refer to either london forces, permanent dipoles and hydrogen bonding


The mark scheme will, most likely, say allow van der Waals when talking about London forces

Spoiler



Thanks for the help guys!

For past papers, is the content for our exam only in f321 and f322? These are the only papers we have done in my class. Are there topics missing from those papers I need to be aware of?
Reply 645
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Cherx
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Original post by Major Wilson
Good luck for tomorrow everyone


Wait wtf... Isn't it on Friday!?
Reply 646
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Cherx
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Omg I had heart palpitations mannn..

Checked my timetable.. It is on Friday. Pleasant surprise to find out it was an evening exam. I though it was in the am but that was the last paper. Ahh yes so happy!!
Original post by Major Wilson
Good luck for tomorrow everyone


Thanks mate
Reply 648
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S.G.
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Does anyone have a prediction on what the extended answer questions could be?
Original post by asinghj
The mark scheme will, most likely, say allow van der Waals when talking about London forces


Yh I think it does, but I would just prefer to say london forces because its the preferred answer
Original post by Internets

Spoiler


Thanks for the help guys!

For past papers, is the content for our exam only in f321 and f322? These are the only papers we have done in my class. Are there topics missing from those papers I need to be aware of?


Ideal gas equation
Maybe of few others but i'm not sure
Does anyone have the mark scheme to the other depth paper that isn't on the ocr website??
http://www.ocr.org.uk/Images/65360-question-paper-unit-f322-chains-energy-and-resources.pdf

q 3b ii why do you times by two? is it because of the 2:1 ratio?


MS has:

(2 x 2.3) / 0.2 = 23 kJ mol-1

The MS would accept 12 kJ mol-1 but not sure if it will this year
Original post by Jitesh
...


The standard enthalpy change of a reaction is the enthalpy change which occurs when equation quantities of materials react under standard conditions, and with everything in its standard state.
I guess it is because of the ratio.
Original post by Vanilla Poison
I guess it is because of the ratio.


I don't fully understand why we times it by two when the moles that reacted was 0.200 ?
Original post by Jitesh
I don't fully understand why we times it by two when the moles that reacted was 0.200 ?

I don't really get why myself, perhaps this will help.
Examiners report:
The mark scheme allowed +12 kJ mol–1 as an alternative answer which is not the enthalpy change of reaction but is the enthalpy change per mole of NH4SCN.
Original post by Vanilla Poison
I don't really get why myself, perhaps this will help.
Examiners report:


Yeah I also read that as well and still don't fully understand, I'm just worried they wouldn't accept enthalpy change per mole of NH4SCN this year.. hmmm

Thanks though!!
Original post by Jitesh
Yeah I also read that as well and still don't fully understand, I'm just worried they wouldn't accept enthalpy change per mole of NH4SCN this year.. hmmm

Thanks though!!

No worries man, I think I kinda get it now. This Wikipedia article is quite good.
https://youtu.be/LUE6tj1-_z4
Last minute mechanisms revision video
:smile: good luck everyone!
Original post by Vanilla Poison
No worries man, I think I kinda get it now. This Wikipedia article is quite good.


Ah, I see now - so it is to do with the molar quantities

Why does it show adding the sum of the stoichiometric number of entity B?

Edit: nevermind misread it

Thanks a bunch! Not seen a question like that before lol
(edited 7 years ago)

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