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# AQA - Unit 5 - Energetics, Redox and Inorganic Chemistry watch

1. (Original post by Tiger_Lilly92)
Hey how did you work out the equation for this question?
The question tells you hydrogen peroxide is converted into O2 so that gives you the half equation:

H2O2 --> O2 +2H+ + 2e-
(remember that the oxidation state of oxygen in H2O2 is only -1)
Oxygen's oxidation state changes from -1 to 0 and there are two so two electrons are given off.

You are supposed to be able to remember the half reaction for the reduction of MnO4- (and Cr2O7(2-) in other questions), which is:

MnO4- + 8H+ + 5e- --> Mn2+ + 4H2O
Manganese's oxidation state changes from +7 to +2 so five electrons are added.

Make the number of electrons on both reactions the same so the oxidation of H2O2 is multiplied by 5 and the reduction of MnO4- is multiplied by 2 (making 10 electrons each).

5H2O2 --> 5O2 +10H+ + 10e-
2MnO4- + 16H+ + 10e- --> 2Mn2+ + 8H2O

Cancel out things that appear on both sides of the equation (in this case H+ and e-) and merge.

5H202 + 2MnO4- + 6H+ ---> 5O2 + 2Mn2+ + 8H2O
2. (Original post by teddyWS)
1)Na(s) -->Na(g)
2) 1/2 Cl2 (g)--> Cl (g)
1) Enthalpy of atomisation of Na
2) Enthalpy of atomisation of Cl
3. Do we have to know the colours of ions such as vanadium ions, manganese ions? Because I wonder why people have a list of 50 colours.
4. does anyone have the jan 11 paper and markscheme?
5. (Original post by SashaLuLu)
ionic bonds are always stronger than covalent bonds. this is due to the strong electrostatic forces between oppositely charged ions. It is easier to break the covalent bonds. It will only be incredulity strong if it is macromolecular. Silicon dioxide is macromolecular.
not always, Na2O is giant ionic, ionic bonds need to be broken to melt it, but it has lower melting point than SiO2 which is a macromolecular, which needs many covalent bonds to be broken.

I thought covalent bonds were stronger than ionic in general?
6. Were there no chem5 papers for jan06? I can't find any
7. (Original post by Raimu)
.
(Original post by jimmy303)

You are supposed to be able to remember the half reaction for the reduction of MnO4- (and Cr2O7(2-) in other questions), which is:
In case you miss this Raimu
8. (Original post by Luke0011)
Page 80, look at the example.

the acylation page? it says nothing about cobalt
9. (Original post by Crowned Temmy)
Do we have to know the colours of ions such as vanadium ions, manganese ions? Because I wonder why people have a list of 50 colours.
colours for vanadium has dropped off the syllabus but we can be given questions on its reactions

theres only 2 we need to knowfor manganese... that is:
MnO4- is purple
Mn2+ Is colourless
10. (Original post by xX.Sabeel.Xx)
colours for vanadium has dropped off the syllabus but we can be given questions on its reactions

theres only 2 we need to knowfor manganese... that is:
MnO4- is purple
Mn2+ Is colourless
I thought Mn 2+ is pale pink
11. I've just gotta finish revising chapter 16, then 13, past papers and review it all again.
12. (Original post by InItToWinItGetIt?)
I thought Mn 2+ is pale pink
Very pale pink, and colourless in low concentrations, is what my tutor told me.
13. (Original post by xX.Sabeel.Xx)
colours for vanadium has dropped off the syllabus but we can be given questions on its reactions

theres only 2 we need to knowfor manganese... that is:
MnO4- is purple
Mn2+ Is colourless
Oh thanks.
14. (Original post by strawberry_cake)
Were there no chem5 papers for jan06? I can't find any
June 03 onwards

http://www.freeexampapers.com/past_p...QA%2F2003+Jun/
15. (Original post by BethBeth)
In case you miss this Raimu
Thank you
16. (Original post by BethBeth)
Very pale pink, and colourless in low concentrations, is what my tutor told me.
Would you get away with pale pink or do they generally prefer you saying colourless?
17. (Original post by Raimu)
Thank you
No probs!
18. (Original post by InItToWinItGetIt?)
Would you get away with pale pink or do they generally prefer you saying colourless?
Both CGP and Nelson Thornes says pale pink, just consulted them Best to stick with that methinks

No idea why someone negged you for this?
19. (Original post by Wish I Could Change This)
the acylation page? it says nothing about cobalt
we have different books then
haha.
20. (Original post by starburst92)
Do we need to know the equations for fuel cells in alkali conditions? If we do what are they? thanks
anyone?

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