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# Wjec ch5 22 june 2016 thread

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1. (Original post by wwwwwwwwwwwf)
HCl at 0.1 mol which was W

and Ch3COOH (or w.e it was) at 0.001 which i think was Y but cant remember
wasnt it the 0.1 conc for the weak acid? I worked it out and the pH came to around 2.96, which coincided with the graph.
2. (Original post by Firestartc)
wasnt it the 0.1 conc for the weak acid? I worked it out and the pH came to around 2.96, which coincided with the graph.
It was 0.1 for both W and Y
3. I got 14% for copper as well
4. (Original post by cfcforever)
It was 0.1 for both W and Y
yea, i was correcting him
5. (Original post by Firestartc)
wasnt it the 0.1 conc for the weak acid? I worked it out and the pH came to around 2.96, which coincided with the graph.
Graph A was strong acid starting at 1pH so was 0.1

Graph B was the weak acid starting at 3pH so was 0.001

-log(0.001) = 3
6. They gave you the value of ka so you had to work out conc of h+, which was around 3 for the 0.1 conc weak acid so i chose that one

(Original post by wwwwwwwwwwwf)
Graph A was strong acid starting at 1pH so was 0.1

Graph B was the weak acid starting at 3pH so was 0.001

-log(0.001) = 3
7. (Original post by wwwwwwwwwwwf)
Graph A was strong acid starting at 1pH so was 0.1

Graph B was the weak acid starting at 3pH so was 0.001

-log(0.001) = 3
It's a weak acid so it doesnt fully dissociate, you need to use Ka
8. (Original post by wwwwwwwwwwwf)
Graph A was strong acid starting at 1pH so was 0.1

Graph B was the weak acid starting at 3pH so was 0.001

-log(0.001) = 3
Can't work it out like that because it's a weak acid and so you have to use the Ka value etc :/
9. (Original post by cfcforever)
It was 0.1 for both W and Y
2nd one was 0.001 because graph started at 3pH -log(0.001) = 3
10. oh ic nvm then
11. (Original post by sumeyyatontus)
Can't work it out like that because it's a weak acid and so you have to use the Ka value etc :/
How sure are you that we will only lose one mark for the rate equation question which we both messed up on? Because we had to write down units also ?
12. (Original post by Firestartc)
How sure are you that we will only lose one mark for the rate equation question which we both messed up on? Because we had to write down units also ?
Well I'm not 100% sure but usually they'd give you both marks from error carried forward, as long as your Units were right for the rate equation you stated
13. (Original post by sumeyyatontus)
Well I'm not 100% sure but usually they'd give you both marks from error carried forward, as long as your Units were right for the rate equation you stated
So if my answers for the question after were all correct including the units? How many marks do they usually drop you?
14. (Original post by sumeyyatontus)
Got all of those same values apart from the Gibbs, forgot to convert the temperature :/
What was 4.9x10-5 the answer to?
15. (Original post by Firestartc)
What was 4.9x10-5 the answer to?
Oh I'm not sure about that one, I just meant for the ones that they'd given which question it was, but for the Kp value in question 3 I think I had 4 point something
16. (Original post by cfcforever)
I got 14% for copper as well
Dw lose a mark that's all due to error carried forward. I also had a 1183 or something for entropy because it was 8 molecules of water used and stuff so I multiplied the entropic by the molecules. Few marks gone there. As for the formation of BaCl2 I had a positive answer of 752. delta H equals all of them plus the enthalpy of formation and just rearranged them:/ don't know it'll it's right or whether it's error carried forward again

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17. Did anyone use Cu (h2o)6 to cucl4 for the ligand substitution question? The 6 marker

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18. (Original post by Rhyss01)
Did anyone use Cu (h2o)6 to cucl4 for the ligand substitution question? The 6 marker

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I used the Cu(H2O)6 to Cu(NH3)4(h2O)2 one, but I'm pretty sure the one you used is also right and will get you the marks
19. What did everyone put for the alkaline salt? I worked at the pH of the water and found it was like 6.2, so said the salt must be slightly alkali to counteract the acidity of the water?

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Updated: June 22, 2016
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