I do not understand how to balance this oxidation-reduction question?

Posted on 2015-09-26 08:33:00 in Chemistry by TONY

I am having trouble identifying the Oxidation and Reduction half for this
Half reaction method of a basic reaction:

Ag(s) + CN^1-(aq) + O2(g) --> Ag(CN)2 ^1-
(aq)

Here's what I don't understand:

1. First of all I am not sure if I got the correct oxidation numbers for the product,
What I did was: CN has a charge of 1-, therefore N=3- and C=2+ and multiplying by the subscript makes their total charge 2-, therefore Ag charge is 2+ (Please correct me if I am wrong)

2. Assuming I did #1 correctly, why is both CN^1- and Ag part of the oxidation half? I thought C and N oxidation number stay the same... (N is -3 and C is 2)

3. Why is O2 in the reduction half when it does not even show up in the product? Do I just assume it's going to make H2O and that has a charge of 2-?

Thanks in advance!

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