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# OCR A 2016 Chemistry A* A-Level Resources watch

1. (Original post by morgantopham)
Hi, thank you for the notes! Why do you do [H+] x [H+] and not just 100 x [H+], why 2 H+ and not just 1?
It was a substitution, originally Kw = [OH-][H+]
when [OH-] = 100[H+] we still need to multiply it by the [H+]
2. (Original post by Danllo)
F321 : 66/90 - B - 73% 10-15% increase
F322 : 125/150 - A - 84% 5-10% increase
F323 : 48/60 - A - 80% Useless because schools cheat
F324 : 27/90 - U - 30% Minimum 20%+ increase should happen
F325 : 75/150 - D - 50% Minimum 10%+ increase should happen
F326 : 51/60 - A - 85% Useless because schools cheat

=392/600 - C

These are my UMS scores (I am a gap year student). I am resitting A2 obvs, but shall I resit F321? I'm not retaking F322 and I'm not retaking the course work. Do u think that's a the best option ? I'd be happy to advise u on what exams to resit if u want.
Eh, depends on grade. Presumably you DON'T want (expect) an A*, so I'll tailor it for that.

F324 NEEDS redoing, F322 may as well be redone, as you can gain some valuable UMS there, with no major extra revision.

F321 is the introductory module, so this will be easier than the rest, if you're feeling like revising the basics again, may also help with F325, though only marginally.

F325 probably should be redone, but is a rather dense module so might add a lot to workload.
3. F321 - C 57/90
F322 - C 98/150
Both exams results really are middle c's
F323 - D 32/60

Overall C - 187/300.

I am retaking both exams after how disastrous f321 went and I feel that I can do so much better in F322 this year. I can retake coursework but only as a private candidate and I don't think I have £500 right now... would absolutely love an A but would be content with a B

Been getting B's consistently with some A's in f324 (minus the 2015 paper, let's hope it's not that bad this year). Possible?

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4. (Original post by Hunnybeebee)
F321 - C 57/90
F322 - C 98/150
Both exams results really are middle c's
F323 - D 32/60

Overall C - 187/300.

I am retaking both exams after how disastrous f321 went and I feel that I can do so much better in F322 this year. I can retake coursework but only as a private candidate and I don't think I have £500 right now... would absolutely love an A but would be content with a B

Been getting B's consistently with some A's in f324 (minus the 2015 paper, let's hope it's not that bad this year). Possible?

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Yes a B is definitely possible and A is also possible.

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5. Not having coursework in the reformed A-Levels has been a revelation. I hate coursework. It really allows me to focus on the theory now.

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6. Can anyone explain what stoichometry actually is and why the ratio is not the same as the number of moles - can't seem to get my head round it.
I feel so stupid asking this now currently doing A2 chemistry and still don't get it :|
7. (Original post by tcameron)
Can anyone explain what stoichometry actually is and why the ratio is not the same as the number of moles - can't seem to get my head round it.
I feel so stupid asking this now currently doing A2 chemistry and still don't get it :|
Stoichiometry is just a way of relating two species that react, in a ratio.

EXAMPLE:

1A + 2B -> 3C

Now usually this would be written as A + 2B -> 3C but I've written the 1 to exaggerate the point.

Now say you have 1 mole of A and 2 moles of B, in this case THE STOICHIOMETRY is equal to the moles.

But if you have say 0.5 moles of A, you cannot say you have 1 mole of A can you. The stoichiometry is then only useful in determining how much of something you produce or react. So if you were told that the reaction goes to completion, you can work out how many moles of B and C you have, (Useful in equilibria).

So the stoichiometry ratios are
1A:2B:3C

So if you have 0.5 moles of A, you will react 2 x 0.5 = 1 mole of B and 3 x 0.5 = 1.5 moles of C will be produced.
8. Hey can someone explain why on the mark scheme it says you have to do conc/mr
How would you answer the first part of the Question?
I understand what to do after but the first part according to mark scheme is confusing me

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9. The reason why you use the formula you quoted is because the mass that is given in the question has units gdm^-3 instead of grams (g).
10. anyone else find f325 Acids, Bases and Buffers module the most disgusting? -__-
11. (Original post by tcameron)
anyone else find f325 Acids, Bases and Buffers module the most disgusting? -__-
Yes. It's a pain in the fxcking backside.
12. (Original post by phdparker)
Yes. It's a pain in the fxcking backside.
Nah it's chill just do a few of the problems.
13. (Original post by tcameron)
anyone else find f325 Acids, Bases and Buffers module the most disgusting? -__-
Is that AS or A2?
14. how do you explain whether or not a reaction is possible with Sn4+ and I-.
15. (Original post by Yesitisi)
Is that AS or A2?
A2
16. (Original post by ForgottenApple)
Nah it's chill just do a few of the problems.
I've been doing past questions on this module, and on the mark scheme of some a question asked to find the concentration of a molecule, they calculate concentration by multiplying a random number by the number of moles of the molecule.
So confused as I thought concentration was always moles÷volume
17. Has anyone tried doing AQA or Edexcel yet ?
18. (Original post by tcameron)
I've been doing past questions on this module, and on the mark scheme of some a question asked to find the concentration of a molecule, they calculate concentration by multiplying a random number by the number of moles of the molecule.
So confused as I thought concentration was always moles÷volume
Find the question. I'll explain anything you can't do.
19. (Original post by Danllo)
Has anyone tried doing AQA or Edexcel yet ?
I did, by about this time. You're going to want to supplement any extra work you can, if you're working towards the top grade it's all about maximizing practice, by using other boards questions of course, but keep your eye on the prize. Don't burn through all of OCR content before moving to another board, DO THEM IN PARALLEL. Exam technique is a huge % of the mark, and trust me it can cost you a grade. It's all well and good knowing the chemistry which practice brings but remember you're passing an exam aswell, specifically OCR's.

I just had a look at my past paper spreadsheet and I did every single OCR paper twice, tracked at least. So if you're serious about getting close to 100% it might be a good idea to do all now, move onto other boards, then returning for a second run at OCR when you've forgotten them in a couple months.
20. (Original post by ForgottenApple)
Find the question. I'll explain anything you can't do.
The question isn't exactly on pH but I don't see how I'm getting this wrong.
Q:
A chemist checked the concentration of aqueous calcium hydroxide, Ca(OH)2, in the sewage water by titration with 5.00x10-3 moldm-3 hydrochloric acid.
Ca(OH)2 + 2HCl -> CaCl2 + 2H2O
The chemist titrated 25cm3 of the sewage watee with 21.35cm3 of HCl to reach the end point of the titration. Calculate the concentration in moldm-3 of the calcium hydroxide in the sewage water.

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