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# OCR B F335 - Chemistry by Design - 13th June 2012

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1. Hiya,

Has anyone got any revision notes to upload?

Thanks, hope everyone's revision is going well!

2. (Original post by Princess Kawaii)
Okay I did my first paper for this topic today and got on the dot B not good when I need an A.

I did f335 June 10 paper and found some questions difficult ...can anyone explain how you would work them out ... I've look at the mark scheme but they don't always lay the answer/working out in steps.

some of the questions are:
- Q4 a(i)

- Q5 e(v)

- Q5 f

Thanks alot
Okay, so Q4 ai) First you need the formula for the combustion of benzene. Benzene is C6H6
soo.. C6H6 + 9O2 -> 6CO2 + 6H2O Just double check this, I only did it quickly

Now we need to work out what that 1.00g of benzene is in mol. So mass= mol x Mr
So 1.00/[6x12+6]
= 1/78 [Haven't rounded cause I've not finished with that number yet]
For every benzene you get 6 CO2 's
So 6x [1/78] = 6/78 mol of CO2
You want the mass so, 6/78 x [12+16x2] = 44/13 = 3.38 g [3sf]

However, it's only a two marker, and it mentions empirical formula so there must be a quicker way using that? Cause I've explained it though it looks longer, so it might be okay doing it that way. I would.

Q5 ev) pH = -log[H+]
Because I haven't done the rest of the question I'm not sure what the value of [H+] is, though I'm sure the first parts lead you towards it. Use one of the equations for Ka or something

I'm also not sure about part f, sorry :/ need to think about it, it might be one that I was given to do, so if no-one else answers maybe I'll do it tomorrow

Hope I helped on q4 though, and I did check that answer
Happy Chemistry[ing]!
3. Just been revision water and enthalpy dissolving and stuff. Not too hard, but it can be confusing.

Ionic substances will not dissolve in non-polar solvent
Covalent substances with never dissolve in polar solvents.

And ionic substances will usually dissolve in polar substance due the attraction of the hydrogen on water to the negative ions and the oxygen on water attracted to positive ions.
4. isit just me or RE THERE THINGS IN F335 WHICH YOU JUST HAVE TO GUESS SOMETIMES :/
5. Do we need to know about Kp for equilibrium constants? Its not in chemical ideas - but its in the revision guide CGP and it appears the specimin paper? What do you guys think?
6. (Original post by Einy)
Do we need to know about Kp for equilibrium constants? Its not in chemical ideas - but its in the revision guide CGP and it appears the specimin paper? What do you guys think?
No we don't. They took it out this year. It still appears int he spec paper because that was written at the begining of the new specification in sept09. Hope that clears it all.
7. (Original post by master_blaster66)
isit just me or RE THERE THINGS IN F335 WHICH YOU JUST HAVE TO GUESS SOMETIMES :/

Sometimes questions pop up on stuff we 'haven't' done. Usually they're only a few marks, my teacher says they're to distinguish the A* from the A students. Don't worry about them, do all the other questions and come back if you have time. They're normally the sort of question you can work out, from what they give you, just read the question carefully. For example it may mention copper [II] something, telling you copper has a plus 2 oxidation state in the compound. They won't put anything in that we can't work out, you just have to understand the chemistry, not just do it, it'll make it alot easier. Unlike maths where you just need to know the routine.

8. (Original post by Tantail)
Sometimes questions pop up on stuff we 'haven't' done. Usually they're only a few marks, my teacher says they're to distinguish the A* from the A students. Don't worry about them, do all the other questions and come back if you have time. They're normally the sort of question you can work out, from what they give you, just read the question carefully. For example it may mention copper [II] something, telling you copper has a plus 2 oxidation state in the compound. They won't put anything in that we can't work out, you just have to understand the chemistry, not just do it, it'll make it alot easier. Unlike maths where you just need to know the routine.

You know for example when it says Copper (II), I understand it has a 2+ charge but how do u know whether whatever is in the brackets is negative or positive? will it always be + ??
9. (Original post by Bi0logical)
You know for example when it says Copper (II), I understand it has a 2+ charge but how do u know whether whatever is in the brackets is negative or positive? will it always be + ??
Usually it's positive, I think. I've never come across a negative one.
10. (Original post by Bi0logical)
You know for example when it says Copper (II), I understand it has a 2+ charge but how do u know whether whatever is in the brackets is negative or positive? will it always be + ??

(Original post by navarre)
Usually it's positive, I think. I've never come across a negative one.
Same. Unless it's specified, I think it's just supposed to be assumed it's positive for Cu (II).
11. (Original post by SimpleGirl)
Same. Unless it's specified, I think it's just supposed to be assumed it's positive for Cu (II).
Metals have a much greater tendency to form positive ions, you like never see negative metal ions, so assume its positive.
thanks
14. (Original post by Beffnaay)
http://www.thestudentroom.co.uk/show....php?t=1999876
i found the markscheeme
15. Thank you!!
16. What did everyone think of the January 2012 paper? Hard or easy?
17. (Original post by Beffnaay)
What did everyone think of the January 2012 paper? Hard or easy?
Wasnt too bad, a little bit of the synoptic stuff got me.
18. Really not ready for this

What do I need to know for storylines?!

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19. (Original post by LexxieK)

What do I need to know for storylines?!

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you always say that every exam season, and always come out with 90% +
20. (Original post by master_blaster66)
you always say that every exam season, and always come out with 90% +
Seriously I've done nothing, urgh. I got an offer which doesn't require chemistry A2 but now I feel bad for doing nothing and know I must!

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