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# Aqa a2 chem5 19th june 2012 Tweet

Chemistry exam discussion - share revision tips in preparation for GCSE, A Level and other chemistry exams and discuss how they went afterwards.

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1. Re: Aqa a2 chem5 19th june 2012

i dont understand how to get the 3:1 ratio?
2. Re: Aqa a2 chem5 19th june 2012
(Original post by masterhr1)
yes, but how does losing heat mean it will stay at 0oC
The process is exothermic. If the heat wasn't lost to the surroundings, then the ice would melt. If the heat is lost to environment, it cant raise the temp, and thus it stays at 0.
3. Re: Aqa a2 chem5 19th june 2012
(Original post by undertaker1)

i dont understand how to get the 3:1 ratio?
3NaOH + H3PO4 ---> Na3PO4 + 3H20

That should help
4. Re: Aqa a2 chem5 19th june 2012
(Original post by masterhr1)
Does this question even make sense:

The freezing of water is an exothermic process. Give one reason why the temperature of a sample of water can stay at a constant value of 0C when it freezes.
Energy is given out when bonds are formed between water molecules, as the state changes from liquid to solid. All the energy is given out to form the bonds and not change the temperature.
5. Re: Aqa a2 chem5 19th june 2012
When the hexaaqua complexes are protonated by water is it an equilibria reaction or a normal one?

eg

[Cu(H2O)6]^2+ + H20 ---> [Cu(H2O)5(-OH)]^+ + H30+
6. Re: Aqa a2 chem5 19th june 2012
For the catalysts and autocatalysis reactions, do you just learn the equations? (like Mn3+ and Fe3+)
7. Re: Aqa a2 chem5 19th june 2012
(Original post by Amy-Rose)
For the catalysts and autocatalysis reactions, do you just learn the equations? (like Mn3+ and Fe3+)
Yes. Or you can learn the half equations and then work out the full one.
8. Re: Aqa a2 chem5 19th june 2012
(Original post by Bugsy)
Yes. Or you can learn the half equations and then work out the full one.
Ah yes, its easy enough to work it out from the half equations. Which do we need to know then? The contact process, Fe2+ in S2O8 2- + I-, and Mn2+ in permanganate and C2O4 2-? They're the only catalysis half equations I have..
9. Re: Aqa a2 chem5 19th june 2012
(Original post by IamBeowulf)
When the hexaaqua complexes are protonated by water is it an equilibria reaction or a normal one?

eg

[Cu(H2O)6]^2+ + H20 ---> [Cu(H2O)5(-OH)]^+ + H30+
I seem to remember one hexaaqua ion doing that, maybe cobalt. adding a base will always form a precipitate first though so redox
10. Re: Aqa a2 chem5 19th june 2012
(Original post by Amy-Rose)
Ah yes, its easy enough to work it out from the half equations. Which do we need to know then? The contact process, Fe2+ in S2O8 2- + I-, and Mn2+ in permanganate and C2O4 2-? They're the only catalysis half equations I have..
Yeah I think for the catalysis that's all, of course there are other's such as the dichromate one and such but they aren't in the catalysis topic (I don't think)
11. Re: Aqa a2 chem5 19th june 2012
(Original post by Bugsy)
Yeah I think for the catalysis that's all, of course there are other's such as the dichromate one and such but they aren't in the catalysis topic (I don't think)
Ah okay cool, thanks. Which are all the others?
12. Re: Aqa a2 chem5 19th june 2012
Wow im finding it so hard to revise ligand substitution from the book.. Theres just a bunch of reactions/equations and I just have to memorise them? If thats the case this is damn hard lol and I think ima fail hard.

Or is there any logic behind the reactions to remember them? The metals with like nh3 and all that stuff
13. Re: Aqa a2 chem5 19th june 2012
Just got 81/100 on June '10

Delighted with that!!!

Just damn colours let me down.... dropped the majority of my marks on it!!
14. Re: Aqa a2 chem5 19th june 2012
(Original post by Angry cucumber)
Just got 81/100 on June '10

Delighted with that!!!

Just damn colours let me down.... dropped the majority of my marks on it!!
do you want a medal?
15. Re: Aqa a2 chem5 19th june 2012
(Original post by IamBeowulf)
When the hexaaqua complexes are protonated by water is it an equilibria reaction or a normal one?

eg

[Cu(H2O)6]^2+ + H20 ---> [Cu(H2O)5(-OH)]^+ + H30+
It's an equilibria reaction
16. Re: Aqa a2 chem5 19th june 2012
(Original post by wibletg)
It's an equilibria reaction
I just wanted to ask you that are all the reactions involving metal complexes with ligands are an equilibria reactions???
17. Re: Aqa a2 chem5 19th june 2012
(Original post by shuaib786)
I just wanted to ask you that are all the reactions involving metal complexes with ligands are an equilibria reactions???
Most, but not all. There are some exceptions.

Adding hydroxide I believe is deprotonation and is NOT in equilibria
18. Re: Aqa a2 chem5 19th june 2012
(Original post by wibletg)
Most, but not all. There are some exceptions.

Adding hydroxide I believe is deprotonation and is NOT in equilibria
So how do you know if they are not???
19. Re: Aqa a2 chem5 19th june 2012
(Original post by shuaib786)
So how do you know if they are not???
I just checked my textbook
20. Re: Aqa a2 chem5 19th june 2012
Can anyone help me with the conventional cell representation. I understand it for most reactions but when there's a reaction say MnO4- + 8H+ + 5e- --> Mn2+ + 4H2O , how exactly do you fit this all into one side of the cell diagram :s I've seen it done in many different ways so if anyone knows the proper (the one the ms accepts) I'd much appreciate it
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