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

1. (Original post by Dinasaurus)
But if it's an addition positive or negative, 0.34 + 2.74 isn't = -2.31

-0.34 + 2.74 is 2.31 not -2.31

(I know the value wasn't 2.74 I am not in the computer now so can't see it but you get what I mean?)

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Ah I read the question wrong. The 2.7V given is the E of the entire cell. That means 2.7=0.4-x. So x has to be a negative
2. (Original post by mamounaltayeb)
Attachment 554407Can someone explain this

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okay i'm not sure but i think it is because :
remember weak acids/buffers can only minimise changes in pH with SMALL additions of acid/alkali, so if you add enough alkali, to counteract this more H+ would be made (equilibrium shift to right) so all the H+ have to react.

we know it is definitely feasible because remember the titration curves: there is one that shows a weak acid can be titrated with a STRONG alkali ( a weak alkali would not work as no vertical line so indicator cannot show equivalence point clearly) so this is how i first figured out that the student was wrong and a titration was possible, then i just had to give a scientific reason why

hope this helps sorry i'm bad at explaining things
3. (Original post by sunsri101)
I did that question and got 0.013 mol/dm^3. I'm pretty sure the answer is wrong by 1 d.p.
Yes I got the same,however when looking at their concentration of H+ it's different to what 10^-8.71 would give,so the way they worked it out is different too
4. (Original post by tcameron)
well I put NH3 + H+ -> NH4+ which is correct but H+ + OH- -> H2O was also correct
the equlibrium still shifts the same way
Great thanks!
5. which transition metals will give hexaamine complex ions, which ones would give (NH3)4(H2O)2 complex ions?
6. What half equations do we need to know by heart for tommorow?
Manganate??
Chromium ??
Iodine ??
Sodium thiosulphate ??

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7. (Original post by lai812matthew)
which transition metals will give hexaamine complex ions, which ones would give (NH3)4(H2O)2 complex ions?
I thought any transition metal could give any complex?

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8. anyone have a proper definition of Kstab? The one in the book makes no sense to me
9. Hi has anyone got the 2015 F325 mark scheme??

10. Can someone help me with this question please?
11. (Original post by TOMWIGHT)
Hi has anyone got the 2015 F325 mark scheme??
Is the paper floating about also??
12. (Original post by Dinasaurus)
I thought any transition metal could give any complex?

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like there is only [Fe(NH3)4(H2O)2]n+ complexes but not [Fe(NH3)6]n+ complexes.
13. (Original post by KB_97)

Can someone help me with this question please?
feo4^2-

There's not much to explain as you kinda just have to remember that feo4 is ferrate ion and it says the charge of iron in the ion is 6+
14. (Original post by mamounaltayeb)
Attachment 554407Can someone explain this

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The student is implying that a weak acid will react less than a strong acid because it has less H+ ions, i.e.: it would form less salt and water than a reaction with strong acid and alkali.

However this is not true. All acids react with alkalis regardless of whether the acid is weak or strong. All the acid will react with a given alkali (given its moles are not limiting). However, the only difference is that a strong acid starts off with a greater amount of H+ in solution because it dissociates completely, but a weak acid only has a small amount of dissociation (less H+ conc in solution). But, as the reaction proceeds, the H+ will be used up in reaction causing it's concentration to decrease. By Chateliar's principle, the weak acid would dissociate more to oppose change of reduced H+. Therefore, all the weak acid will eventually dissociate and react with alkali.

Weak acids just take longer to react, but the reaction is the same. Hence why the student is incorrect with their statement.

Hope this helps!!
15. Any predictions for tomorrow?
16. (Original post by KB_97)

Can someone help me with this question please?
What oxidation state of iron can we associate with red?
Ignore that read it wrong
What does VI mean?
17. (Original post by Magicalgeofray)
Is the paper floating about also??
I've attached F325 June 2015 official paper and mark scheme for those of you all that are asking
Attached Images
18. F325_-_EXAM_PAPER__Jun_2015_.pdf (517.3 KB, 54 views)
19. F325_-_Markscheme__Jun_2015_.pdf (626.1 KB, 46 views)
20. (Original post by KB_97)

Can someone help me with this question please?
ferrate (VI). fe have od of 6. total charge= -2. 6+n= -2, n= -8, one oxygen charge: -2.
-8/-2 =4. feo4 2- confirmed.
21. (Original post by Roses98)
I've attached F325 June 2015 official paper and mark scheme for those of you all that are asking
Cheers boi
22. (Original post by sunsri101)
I did that question and got 0.013 mol/dm^3. I'm pretty sure the answer is wrong by 1 d.p.
I got the same, don't understand the ms

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