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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 11234
What did they mean by use a different symbol for oxygen and what did we have to do


It's a bit blurry but the top circle on the Oxygen I drew as a different symbol but I was not sure if it meant different as in a circle when uses crosses to represent it??

Original post by HarrisonGCSE
For the enthalpy change of reaction one i got confused - mainly regarding how many moles i had to divide the energy released by. For combustion u take the moles of the thing being combusted, for neutrilisation u take the moles of water, and for formation u take the compound. What on earth do u take for reaction?


Molar quantities in a given chemical equation
Reply 262
Avatar for 2kk2
2kk2
how much marks will do u think you would lose if you missed out the - sign in the q value
Original post by Jitesh
100cm3 I think you had to use (100g)


No. For that question they gave conc and vol. So you can work out the moles from that. And then using the moles, you can work out mass by doing moles x mr. That would given you the mass in g which is what you need to do q=mct
Original post by Fish40
Yes I had that, but divided my q=4.736 KJ or something by 0.150


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Think I got same kJ but maybe different moles as I got -58.5 or something
Someone do an unofficial mark scheme! I have no idea if that paper went well or averagely.
Reply 266
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SP98
8
What was the concentration of KI?
Reply 267
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456CJ
2
What did u guys get for water of crystilaztion
I got cr3cl10.18h20
That was so easy wtf


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Original post by A Sajid
No. For that question they gave conc and vol. So you can work out the moles from that. And then using the moles, you can work out mass by doing moles x mr. That would given you the mass in g which is what you need to do q=mct


Are you sure? There's a very similar question to what came up on page 132 of the Oxford textbook (A-level edition)
Original post by 2kk2
how much marks will do u think you would lose if you missed out the - sign in the q value


1 normally
Reply 271
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S.G.
22
Original post by 456CJ
What did u guys get for water of crystilaztion
I got cr3cl10.18h20


CrCl3.6H2O
Reply 272
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S.G.
22
Original post by HarrisonGCSE
For the enthalpy change of reaction one i got confused - mainly regarding how many moles i had to divide the energy released by. For combustion u take the moles of the thing being combusted, for neutrilisation u take the moles of water, and for formation u take the compound. What on earth do u take for reaction?


Molar quantities given in equation
Has anyone seen the unofficial mark scheme?
Original post by SGHD26716
CrCl3.6H2O


Was it not CrCl3.8H20 ? I think I remember getting 8 Oxygens

Might have been 6
Reply 275
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S.G.
22
Original post by Jitesh
It's a bit blurry but the top circle on the Oxygen I drew as a different symbol but I was not sure if it meant different as in a circle when uses crosses to represent it??


I did this but accidentally for some reason put Ni instead of N. How many marks would be lost?
Original post by SGHD26716
CrCl3.6H2O


Same :yy:
Reply 277
Avatar for 2kk2
2kk2
was the q value 4.something in kJ before working out the per mole??
Original post by Fish40
I'm an idiot, didn't write a minus, so you divided your q by 0.075 mol and not 0.150mol, why?


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You had to do 50cm^3 x 1.5moldm^3 not 100cm^3
Reply 279
Avatar for S.G.
S.G.
22
Original post by Jitesh
Was it not CrCl3.8H20 ? I think I remember getting 8 Oxygens

Might have been 6

I got 12 hydrogens and 6 oxygens and that goes 6 times for H2O. That what I did anyway.

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