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OCR Chemistry B (Salters) Thursday 10th January Discussion

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Reply 220
Original post by xOsugaplumfairy
An unofficial mark scheme is not needed! It will just worry everyone more. Just wait till the 8th for results :smile: Hopefully I scraped a B. Because I counted 12 marks I was unsure/knew were wrong..
urmm speek for yourself I want an unofficial markscheme, just don't LOOK.
Reply 221
Original post by Maat
CeO2
I got that too
Reply 222
I totally messed up the bond angles one :'(, that's ike 6 marks gone, do you guys think it will be low or high grade boundaries
Reply 223
bond angles one was 120 and then 120 again?
Original post by Maat
bond angles one was 120 and then 120 again?


I thought it was 120 and then 109.
May be wrong though :P

ALSO: I also thought that cycloalkanes and arenes are products of reforming. I put arenes.
(edited 11 years ago)
Reply 225
Original post by Whangdoodle
I thought it was 120 and then 109.
May be wrong though :P

ALSO: I also thought that cycloalkanes and arenes are products of reforming. I put arenes.


You are correct. Angle 'B' (first question) was 120 and angle 'A' was 109. Hence angle 'A' was smaller than angle 'B'.

Arenes is also correct. Cycloalkanes would also have been right.
Okay so grade boundaries will definitely be high, and if it's gonna be anything like the June 2012 one, the mark scheme will be very picky too.
I also wrote 'large complex network with covalent bonding' for the SiO2 q. doubt that would get me a mark, ugh.
Reply 228
Original post by Problematique
Okay so grade boundaries will definitely be high, and if it's gonna be anything like the June 2012 one, the mark scheme will be very picky too.

awww no don't say that :'(
Reply 229
Please someone do and unofficial mark scheme :'(
Reply 230
did they ask for the shape as well ?
Reply 231
Original post by nksunny
did they ask for the shape as well ?


No, just bond angles. Though the MS might give a mark for shape... Who knows?
Unofficial mark scheme anyone please ?? :colondollar:
I know this may sound like a silly question, but for the calculation questions provided you have the correct answer in the working out space, does it matter if you don't then re-write the answer in the space provided with the dotted lines they give? I'm having a stress that in my panic and rushing I forgot to do that and they might be really harsh and not allow it :eek:
hey guys i have the paper :biggrin:
Reply 235
I think the paper went very well, I have a question though about two questions which confused me only slightly ...

One was the energy density one, I put 47,000. That threw me off because it asked for 2 sig. fig. and with a number that big I was doubting myself whether I did it the right way.

Another one, which asked you about calculating enthalpy changes in a combustion reaction ... asking what other piece of information was needed to calculate it ..... I put something like "The mass of Hydrocarbon A that was burnt / used in the combustion reaction" .... other people were talking about Identifying the starting mass and final mass ... would I have got the mark for that question though?

Looking at this thread though and talking to my teacher I think that is all that bothered me. So I think I have potentially lost 2-3 marks.
Original post by Quiggle
I think the paper went very well, I have a question though about two questions which confused me only slightly ...

One was the energy density one, I put 47,000. That threw me off because it asked for 2 sig. fig. and with a number that big I was doubting myself whether I did it the right way.


Did it definitely say to 2 significant figures?
Reply 237
Original post by smileitsfree
hey guys i have the paper :biggrin:


how?
Reply 238
I have a feeling your answer may not be true, the first question we worked out the energy transferred to water, they gave us the volume of water ... I think they had us assume that 200cm^3 of water is equal to 200grams.

Original post by SherlockHolmes
Did it definitely say to 2 significant figures?


Yes, definitely 2 significant figures and not decimal places.. I had to read it over 3 times just to make sure I wasn't being stupid

The question gave us the energy density per mole, which was something like -5400 kJ mol^-1
We are asked to find out the kJ per kilogram.
We were given the Ar of the molecule, something like 112.

So I found the amount of moles per kilogram .... 1000 / 112. Multiplied the moles by the value above (5400).
Obviously these are rough estimates of what was given, I can't remember the exact values.
But I would have got a value of about 47321, but below <47500.
Then it asked for 2 sig fig. in the answer.
The answer isn't a negative value as itis energy per kilogram and not an enthalpy change.
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3 reps for next page :d

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