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# ocr a f325 revision thread watch

1. Does anyone else feel really tired? I feel really sleepy and exam is in 2/3 hrs -_-
2. What do we do when it's diprotonic?

Write an expression of kc for:
2HCOOH + ba(oh)2 --> (hcoo-)2 ba2+ + 2h20

The (hcoo-)2 ba2+ is the salt.
Anyone know what kc would be? The expression that is

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3. (Original post by georgiaaaxo)
haha thanks! so what exactly are you dividing by two? are you dividing the (q/moles) by 2?

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Yes
4. 2.c NO2 reacts with CO emitted from car exhausts in the following rxn:

NO2 + CO -----> NO + CO2

Rate equation for this reaction is rate={NO2}2

Suggest 2 step rxn mechanism for this rxn that is consistent with the kinetic data and overall equation.

P.S june 2006 paper at http://pastpapers.org/A2/chemistry/u...ne_2816_01.pdf

thnx
5. (Original post by Namod)
Yes
ok thanks! I think I got it finally

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6. having a blonde moment: would there ever be h2o in a Kc expression???
I know you don't include it in kstab, is there anywhere where you would include h2o?

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7. (Original post by Janjua)
2.c NO2 reacts with CO emitted from car exhausts in the following rxn:

NO2 + CO -----> NO + CO2

Rate equation for this reaction is rate={NO2}2

Suggest 2 step rxn mechanism for this rxn that is consistent with the kinetic data and overall equation.

P.S june 2006 paper at http://pastpapers.org/A2/chemistry/u...ne_2816_01.pdf

thnx
I would do:
2NO2 -> 2NO + O2
O2 + 2CO --> 2CO2
8. (Original post by MathsNerd1)
Lets do this!!!
Come on!!
9. (Original post by georgiaaaxo)
having a blonde moment: would there ever be h2o in a Kc expression???
I know you don't include it in kstab, is there anywhere where you would include h2o?

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Yep, it's in Kc if it's a reactant or product!
The thing in Kstab is that because the whole thing is in solution, the conc of water is always going to stay relatively constant.
10. (Original post by Myocardium)
Does anyone else feel really tired? I feel really sleepy and exam is in 2/3 hrs -_-
take a little nap so you will be refreshed for the exams.
11. (Original post by Holz888)
I would do:
2NO2 -> 2NO + O2
O2 + 2CO --> 2CO2
I did 2NO2 ---> NO + NO3
NO3 + CO ---> NO2 + CO2

Just to show another alternative really
12. (Original post by Holz888)
Yep, it's in Kc if it's a reactant or product!
The thing in Kstab is that because the whole thing is in solution, the conc of water is always going to stay relatively constant.
okay thankyou for clarifying!!!

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13. How do I do c i? I get so confused when working out the second half equation! Can anyone suggest a method to approach these questions with? Thanks x

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14. (Original post by Holz888)
Yep, it's in Kc if it's a reactant or product!
The thing in Kstab is that because the whole thing is in solution, the conc of water is always going to stay relatively constant.
I thought we didn't include it if it was the solvent being used in the reaction?
15. (Original post by MathsNerd1)
I thought we didn't include it if it was the solvent being used in the reaction?
I was never taught this :/
I guess my best example is a esterification - the H2O is always in the Kc expression. But yeah, that does make sense

16. I got 0.08 mol but why is it finally 0.8 mol in the answer as well as commentary? Another error?
17. (Original post by v :))

How do I do c i? I get so confused when working out the second half equation! Can anyone suggest a method to approach these questions with? Thanks x

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Hey,

Work backwards from the overall equation. Everything in that half equation, cancel it from the overall equation. Then form the second half equation from what you have left.
18. (Original post by Holz888)
I would do:
2NO2 -> 2NO + O2
O2 + 2CO --> 2CO2
Doesn't the rate determining step supposed to lead to the original equation in this case, the rxn btw NO2 + CO ----> NO + CO2 ?

Sorry for bothering you just get stuck at rate determining step.
19. Okay quick question!
January 2011, q7b)ii)

They got the formula: 2H2O + 2I- + 2NO2- = 2NO + I2 + 4OH-

But using the method given in the book I get:
H20 + 2I- + NO2- = I2 + 2OH- + NO

Both equations are balanced(or are they?), but the mark scheme does not even talk about the one I got. The strange thing is that theyre not even multiples of each other!

20. Any last minute predictions on whats going to come up?

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