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OCR Chemistry A, paper 3 unofficial markscheme 2017

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Reply 80
Avatar for Jitesh
Jitesh
14
Original post by Toffo132
So the uncertainty in the smallest mass difference? (1.24) or both/bigger one (25.75g)


I think the bigger one..not sure what I did tbh it was badly written
Original post by studentsixth
Did you continue on to do the chiral question? Because you will get error carried forward marks for this anyways. 4/6 is a safe bet

I almost completely messed up the question (took the titre to be of the acid not NaOH and was stuck with an impossible Mr for ageees) and only noticed about 2 minutes from the end so I ended up misreading the question and drawing out all the enantiomers instead of just starring them

Also for question 3c) (the COOOH one) shouldn't the functional group be O=C-O-O-R??
Reply 82
Avatar for Toffo132
Toffo132
OP
9
Original post by Monkeyyyy
I almost completely messed up the question (took the titre to be of the acid not NaOH and was stuck with an impossible Mr for ageees) and only noticed about 2 minutes from the end so I ended up misreading the question and drawing out all the enantiomers instead of just starring them

Also for question 3c) (the COOOH one) shouldn't the functional group be O=C-O-O-R??


Nope - but the one in the OP is wrong.
https://gyazo.com/7aaa19144d9708d721e09bedc2eda0e4
Reply 83
Avatar for samwray
samwray
1
8.jpgfor the equilibrium question, I didn't include H2O as its a liquid, so multipled Kc by 0.0500^2 then divided by 250/1000 - is that correct? Thanks for emailing the paper by the way!
Original post by Toffo132
Nope - but the one in the OP is wrong.
https://gyazo.com/7aaa19144d9708d721e09bedc2eda0e4


That's what I meant sorry I forgot it was an OH not OR at the end
I feel like the grade boundaries are going to be low for that exam.
Original post by RhiannonScott99
I feel like the grade boundaries are going to be low for that exam.


It's hard to predict. People who had a very thorough knowledge of chemistry will have done well. Those that were not so confident and those that didn't finish the exam on time will possibly bring the boundaries low. Overall, we'll just have to see how much of a skew there is. I don't think there will be *much* to be honest but I love surprises
Yeah, I just feel like it will because a few of the questions were so different from the mock. Also, a lot of people found it difficult so I'm praying :wink:
You know for the last question if i didnt link each test to the molecule how many marks will i get knocked off?? Eg i said react with br2 and those with the double bond will decolourise, but i didnt specifically say which molecules. Also what is the correct order for the last one? I think i messed up.... did test for alkene first, then 2,4 dnph, then tollens, and then oxidation of alcohols - looking back ive really messed it up
Original post by studentsixth
It's hard to predict. People who had a very thorough knowledge of chemistry will have done well. Those that were not so confident and those that didn't finish the exam on time will possibly bring the boundaries low. Overall, we'll just have to see how much of a skew there is. I don't think there will be *much* to be honest but I love surprises


206 for an A overall?
Original post by epistasis
206 for an A overall?


Yeah I think so.
Original post by studentsixth
Yeah I think so.


what do you think you got smexy
Original post by epistasis
what do you think you got smexy


Better than Biology lol

Maybe scraping my A* but wouldn't be surprised if it was less tbh
Reply 93
Avatar for ERBP
ERBP
1
'd) Volume = 188dm^3 | 181 if you use x=6 [4]'
how did you get this? did anyone else get 201dm^3?
Original post by ERBP
'd) Volume = 188dm^3 | 181 if you use x=6 [4]'
how did you get this? did anyone else get 201dm^3?


pV = nRT?
Reply 95
Avatar for Toffo132
Toffo132
OP
9
Original post by ERBP
'd) Volume = 188dm^3 | 181 if you use x=6 [4]'
how did you get this? did anyone else get 201dm^3?


PV=nRT.
n=1000/104=8.38
R=8.314
T=273
P=101000

so V=0.1883m^3 so 188dm^3
you likely calculated n wrong
Original post by Toffo132
PV=nRT.
n=1000/104=8.38
R=8.314
T=273
P=101000

so V=0.1883m^3 so 188dm^3
you likely calculated n wrong


wasn't it 10^6/104? 1 kg?
Reply 97
Avatar for Toffo132
Toffo132
OP
9
Original post by tizzaclaire98
wasn't it 10^6/104? 1 kg?


1kg is 1000g.
Original post by Toffo132
1kg is 1000g.


Oh. My God... I feel so incredibly stupid... totally messed up that question... I incorrectly calculated n (wrong mass AND wrong mr) but all other values were right and I got the right value given my wrong n val. How many marks do you think? how many was it overall?
Reply 99
Avatar for ERBP
ERBP
1
Original post by Toffo132
PV=nRT.
n=1000/104=8.38
R=8.314
T=273
P=101000

so V=0.1883m^3 so 188dm^3
you likely calculated n wrong


**** then, didnt use pv=nrt because assumed it was under standard conditions as 101kPa is standard conditions and as is 273K. used n=V/24 instead.
the joys of overthinking hahaha

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