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Edexcel A2 Chemistry Exams -6CH04 (14th June) and 6CH05 (22nd June) Discussion Thread watch

1. Please can someone explain the second marking point on the markscheme for this question? I don't get what it means by [H+] is greater than expected. I get how the equilibrium shifts to the right, but not this "greater than expected thing". Can someone please explain this? Thanks

2. sup guys. Has anyone ever seen a mark scheme where they don't accept displayed formula when the question asks for structural?
3. Goiys what's the formula for % uncertainty again?
4. (Original post by Don Pedro K.)
Goiys what's the formula for % uncertainty again?
error/value*100

e.g if a temperature is measure at 25 degrees and the error is +-0.5 degrees, 0.5/25*100
5. (Original post by Funky_Giraffe)
Please can someone explain the second marking point on the markscheme for this question? I don't get what it means by [H+] is greater than expected. I get how the equilibrium shifts to the right, but not this "greater than expected thing". Can someone please explain this? Thanks

I think what they're saying is that with ethanoic acid, you get the usual dilution by a factor of 10 and thus increase by 1.0 but because of the equilibrium that ethanoic acid forms with water, dilution shifts the equilibrium to the right so more H+ ions are produced, meaning that the pH doesn't increase as much?
6. (Original post by Don Pedro K.)
I think what they're saying is that with ethanoic acid, you get the usual dilution by a factor of 10 and thus increase by 1.0 but because of the equilibrium that ethanoic acid forms with water, dilution shifts the equilibrium to the right so more H+ ions are produced, meaning that the pH doesn't increase as much?
Oh I see So it's kind of comparing the full dissociation of HCl with the partial dissociation of CH3COOH?
7. What are the factors that affect titre values?

Like what happens if a larger mass is used?
8. (Original post by Funky_Giraffe)
Oh I see So it's kind of comparing the full dissociation of HCl with the partial dissociation of CH3COOH?
That's what it seems like, because if you think about it, HCl(g) + H2O(l) --> H3O+Cl-(aq) is not an equilibrium, so dilution doesn't "shift" anything I think? But with ethanoic acid it does form an equilibrium so Le Chatalier's principles apply. I may be wrong though but this is my reasoning xD
9. What's the error in a burette? +-0.05cm3?
10. Guys how was the paper? I found it pretty solid, the MCQ's were amazing
Although I'm worried about the last 5 marks
11. i have a few questions

- what if the product in an equilibrium is only a solid, and they ask you to determine the expression for kp, would you divide the reactants by 1?

- When using the lattice enthalpies from the data booklet do you use the theoretical or experimental value ?

- does hydrogenation only break C=C bonds or can it also break C=O into C-OH seeing as hydrogenation is the addition of hydrogen to break double bonds!?

- and with the definition for Dynamic equilibria would you describe it as ' The rate of the forward and backward reaction are equal , and the concentration of products and reactants are the SAME OR EQUAL' ?
12. Is the IAL thread? If not, ignore my post above
13. (Original post by azefayuu)
Guys how was the paper? I found it pretty solid, the MCQ's were amazing
Although I'm worried about the last 5 marks
the paper is to be taken at 1:30 ?
14. (Original post by azefayuu)
Is the IAL thread? If not, ignore my post above
could you tell us what were the main topics that came up ?
because there usually very similar
15. (Original post by tayloryeah)
could you tell us what were the main topics that came up ?
because there usually very similar
Haha no.
Different timezones.
16. (Original post by tayloryeah)
could you tell us what were the main topics that came up ?
because there usually very similar
he is lying ignore him,
17. (Original post by Don Pedro K.)
I'm afraid you forgot to do something natcupine!!

ihaspotato You would have to double the 38.5 sine the H2 is in a 2:1 molar ratio to the CH3OH So it's 77.5 - 77 = 0.5 moles
Oh yeah!! 2 hours before the exam lol Thanks for correcting me!
18. how do you work out order of reaction when other concentrations are changing?

E.G. question 14 cii
http://qualifications.pearson.com/co...e_20150610.pdf
19. how do you work out order of reaction when other concentrations are changing eg q 14 cii
http://qualifications.pearson.com/co...e_20150610.pdf
20. (Original post by natcupine)
Oh yeah!! 2 hours before the exam lol Thanks for correcting me!
No problem

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