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

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Reply 60
Hiya,

Has anyone got any revision notes to upload?

Thanks, hope everyone's revision is going well!

:smile:
Original post by Princess Kawaii
Okay I did my first paper for this topic today and got on the dot B :frown: 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

Here's the paper: http://pdf.ocr.org.uk/download/pp_10_jun/ocr_57559_pp_10_jun_gce_f335.pdf?

Thanks alot :smile:


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 :smile:

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 :smile:

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 :smile:

Hope I helped on q4 though, and I did check that answer :wink:
Happy Chemistry[ing]!
(edited 11 years ago)
Reply 62
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.
isit just me or RE THERE THINGS IN F335 WHICH YOU JUST HAVE TO GUESS SOMETIMES :/
Reply 64
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?
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. :smile: 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.
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. :smile:

Sorry about the lengthy text, hope that is helpful :smile:
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. :smile:

Sorry about the lengthy text, hope that is helpful :smile:


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 + ??
Reply 68
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.
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).
Reply 70
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.
can someone upload the f335 jan12 MS please
thanks
Reply 72
Yeah, will someone please upload the January mark scheme! :biggrin:
Original post by Beffnaay
Yeah, will someone please upload the January mark scheme! :biggrin:


http://www.thestudentroom.co.uk/showthread.php?t=1999876
i found the markscheeme
Reply 74
Thank you!! :biggrin:
Reply 75
What did everyone think of the January 2012 paper? Hard or easy?
Reply 76
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.
Reply 77
Really not ready for this

What do I need to know for storylines?!


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Original post by LexxieK
Really not ready for this

What do I need to know for storylines?!


This was posted from The Student Room's iPhone/iPad App


you always say that every exam season, and always come out with 90% +
Reply 79
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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