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# OCR A2 CHEMISTRY F324 and F325- 14th and 22nd June 2016- OFFICIAL THREAD watch

1. Anyone remember whether the other factor for isomerism was based on just Cis isomerism or both cis-trans?
2. Could someone please help me with calculating the pH of strong bases please? I understand that whenever you have water you have the H20 ⇌ H+ + OH- equilibrium set up and I understand that you can assume from this:
Ka = [H+] [OH-] and therefore .... Kw = [H+] [OH-]
---------------
[H20]

but how do you use this to work out the [H+] when you add a base? surelyby adding OH- you are using up some of the H+ to produce H20, these are in the same proportions so what [H+] or [OH-] decreases by H20 increases by therefore you in the case of...

[H+] [OH-]
---------------
[H20

] you're then dividing a smaller number by a bigger number so how does KW remain constant? surely it would decrease? meaning you can't use 1 x10-14
3. (Original post by mcdcph)
Could someone please help me with calculating the pH of strong bases please? I understand that whenever you have water you have the H20 ⇌ H+ + OH- equilibrium set up and I understand that you can assume from this:
Ka = [H+] [OH-] and therefore .... Kw = [H+] [OH-]
---------------
[H20]

but how do you use this to work out the [H+] when you add a base? surelyby adding OH- you are using up some of the H+ to produce H20, these are in the same proportions so what [H+] or [OH-] decreases by H20 increases by therefore you in the case of...

[H+] [OH-]
---------------
[H20

] you're then dividing a smaller number by a bigger number so how does KW remain constant? surely it would decrease? meaning you can't use 1 x10-14
for a strong base the oh- conc is the same as the concentration of added alkali since all the alkali dissociates. therefore you use the kw equation. you know the conc of oh- and the value of kw(1.0x10-14) and so rearrange to find to H+ conc. then use ph= -log(h+) to get ur ph. dont worry about the concentration of of h+ and h20 decreasing and increasing it will only confuse you.
5. (Original post by Can't think name)
Guys how many marks was the 3 chiral carbon question?
2 marks!

1st mark for drawing tripeptide
2nd mark for labelling chiral carbons

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6. (Original post by Reg1234567890)
Anyone remember whether the other factor for isomerism was based on just Cis isomerism or both cis-trans?
I believe it was both. Something to do with the fact that both carbons holding the bond have a group attached?
7. (Original post by Reg1234567890)
Anyone remember whether the other factor for isomerism was based on just Cis isomerism or both cis-trans?
You can't have cis isomerism without trans isomerism? They come as a pair, they're not mutually exclusive.

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8. (Original post by AsheColdwater)
I believe it was both. Something to do with the fact that both carbons holding the bond have a group attached?
It's to do with the fact that each carbon atom on either side of the C=C double bond is bonded to 2 different groups.

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9. (Original post by GetOverHere)
It's to do with the fact that each carbon atom on either side of the C=C double bond is bonded to 2 different groups.

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where one of them are the same on both carbons (H)
10. (Original post by HediIsLord)
where one of them are the same on both carbons (H)
I was about to disagree, then saw we were talking about cis-trans rather than E/Z, where it doesn't have to have 1 group that's the same on both C atoms. You don't have to specify that though, saying 2 different groups on either side is sufficient.
11. (Original post by GetOverHere;[url="tel:65815161")
65815161[/url]]I was about to disagree, then saw we were talking about cis-trans rather than E/Z, where it doesn't have to have 1 group that's the same on both C atoms. You don't have to specify that though, saying 2 different groups on either side is sufficient.
Think I gave answer for why cis, would I get mark for saying that two of the same atom/groups of atoms are bonded to each C of c=c are on same side of c=c
12. (Original post by Reg1234567890)
Think I gave answer for why cis, would I get mark for saying that two of the same atom/groups of atoms are bonded to each C of c=c are on same side of c=c
I don't think so, sounds a bit contradictory IMO.
13. Hey Guys,
Has anyone been given the OCR Sample not the one linked below but the one that OCR send to teachers as an example?
thanks
http://www.ocr.org.uk/Images/171751-...-materials.
14. Would hextet instead of sextet or multiplet be awarded the mark?
15. (Original post by GetOverHere)
I don't think so, sounds a bit contradictory IMO.
Your opinion for marks for an A?
16. (Original post by GetOverHere)
I was about to disagree, then saw we were talking about cis-trans rather than E/Z, where it doesn't have to have 1 group that's the same on both C atoms. You don't have to specify that though, saying 2 different groups on either side is sufficient.
said both to be safe
assumed it would be necessary given the emphasis on cis rather than e/z
17. I did all of my diagrams (displayed formulae and mechanisms) in pencil but ALL of my writing in black pen. That's okay right?

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18. (Original post by HediIsLord;[url="tel:65817089")
65817089[/url]]said both to be safe
assumed it would be necessary given the emphasis on cis rather than e/z
This is what I mean emphasis on cis I can't remember it asking about trans
19. (Original post by nae_xo)
I did all of my diagrams (displayed formulae and mechanisms) in pencil but ALL of my writing in black pen. That's okay right?

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should be fine, does say diagrams can be done in pencil

I usually do pencil then pen once I'm sure it's right, rub out the pencil after
20. (Original post by Reg1234567890)
This is what I mean emphasis on cis I can't remember it asking about trans
I think it did say cis-trans

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