Redox HELP!!! thanks you

[jack_chay]

what about the h2o?

[psyxwar]

Well, compare the oxidation numbers of the elements in H₂O and the products which have H and O. What can you see?

[jack_chay]

I know on the left side H = 2+  o+2-,

not sure about the right side

[psyxwar]

I know on the left side H = 2+  o+2-,

not sure about the right side

Alright, remember that in H₂O there are 2 hydrogens and one oxygen. So yeah, both hydrogens together are +2, but you can't say they are individually +2: they are individually +1.

Cd + NiO2 +2H2O ---> Cd(OH)2 + Ni(OH)2

Cd(OH)2: we know that oxygen and hydrogen under most circumstances will have -2 (exceptions are when oxygen is with fluorine, in a superoxide, peroxide) and +1 (exceptions are when hydrogen is bonded to something less electronegative than it, ie. in hydrides (NaH)) respectively. Alternatively, OH- is an overall -1, and we know the constituent elements must have oxidation numbers that add up to the net charge of the element. Hence, oxygen is still -2 here and hydrogen is still +1.

Ni(OH)2: same thing here.

So as we can see, the hydrogens and oxygens are not oxidised or reduced.

[jack_chay]

yes thank you so so much psyxwar:)

[jgoudie]

This might sound a bit like advertising, but it fits the topic:
The videos below might help a little bit if you are confused on these topics. 

Assigning oxidation numbers: http://www.youtube.com/watch?v=sTil_in5KbA&feature=share&list=PL192EE07242D5019A
Balancing complex redox equations: http://www.youtube.com/watch?v=IFr8JdqSAa8&list=PL192EE07242D5019A&index=23
Questions involving redox: http://www.youtube.com/watch?v=CotFqedMVVA&list=PL192EE07242D5019A&index=24
Galvanic cells: http://www.youtube.com/watch?v=2TzDa2zQYF8&list=PL192EE07242D5019A&index=27
Drawing galvanic cells: http://www.youtube.com/watch?v=srJM5brLbFI&list=PL192EE07242D5019A&index=28
Rust and stuff: http://www.youtube.com/watch?v=CWOPCVj-esM&list=PL192EE07242D5019A&index=29

You can see a link to the youtube channel below also.  (and the unit 2 chemisode app just came out on the app store: yep that one was a straight out advertising)

[jack_chay]

in 2Fe(OH)2 + H2O2 --->  2Fe(OH)3

I know Fe is oxidised because from Fe 2+ it turned into Fe 3+, but what about H2O2, is it reduced and how, I can't work out the oxidation number method...

thank you in advance

[jack_chay]

yup thank you jgoudie, i'll check them out

[psyxwar]

Here's one of the special cases I mentioned for oxygen:

Hydrogen peroxide, H₂O₂ contains the peroxide ion, O₂^2- In peroxides, oxygen's oxidation number is only -1.

[lzxnl]

in 2Fe(OH)2 + H2O2 --->  2Fe(OH)3

I know Fe is oxidised because from Fe 2+ it turned into Fe 3+, but what about H2O2, is it reduced and how, I can't work out the oxidation number method...

thank you in advance

Hydrogen peroxide is covalent and so does NOT contain the peroxide ion.
What it does have, however, is an oxygen-oxygen bond. The structure looks like H-O-O-H. As you can see, as oxygen is more electronegative than hydrogen, oxygen gains an electron and so has oxidation state of -1. When bonded to another identical atom, oxygen does not gain or lose an electron.

[psyxwar]

ah, fair enough. My bad!

[jack_chay]

um.. sorry but
how does it prove that h2o2 is reduced?

[psyxwar]

Well, oxygen is going from -1 to -2.

[jack_chay]

how did you get that?

[psyxwar]

how did you get that?

I'm referring to the oxygen in the hydrogen peroxide specifically. The oxygen in the other reactant doesn't change in oxidation number.