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

1. (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??

2. (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
3. how much marks will do u think you would lose if you missed out the - sign in the q value
4. (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
5. (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
6. Someone do an unofficial mark scheme! I have no idea if that paper went well or averagely.
7. What was the concentration of KI?
8. What did u guys get for water of crystilaztion
I got cr3cl10.18h20
9. That was so easy wtf

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10. (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)
11. (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
12. (Original post by 456CJ)
What did u guys get for water of crystilaztion
I got cr3cl10.18h20
CrCl3.6H2O
13. (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
14. Has anyone seen the unofficial mark scheme?
15. (Original post by SGHD26716)
CrCl3.6H2O
Was it not CrCl3.8H20 ? I think I remember getting 8 Oxygens

Might have been 6
16. (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?
17. (Original post by SGHD26716)
CrCl3.6H2O
Same
18. was the q value 4.something in kJ before working out the per mole??
19. (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
20. (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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