How do you balance this redox equation?

Question

Balance the following equation in basic solution using the lowest possible integers and give the coefficient of hydroxide ion.

Au(s) O2(g) CN- => [Au(CN)2]- (aq) H2O2(aq)

I can't figure out the oxidation numbers for [Au(CN)2]- in order to balance this equation.

The answer for the coefficient of OH- is 2. Can someone show me how they get this?

Answer 1

Au + 2 CN(-) = [Au(CN)2]- + 1 e-   (a one-electron oxidation)

O2 + 2 H2O  + 2 e- = H2O2 + 2 OH(-)   a two-electron reduction

2 Au + 4 CN(-)  = 2 [Au(CN)2]- + 2 e-  (now a two-electron oxidation because I doubled everything)

Add together

O2 + 2 Au + 4 CN(-) + 2 H2O = H2O2 + 2 OH(-) + 2 [Au(CN)2]-

If you take Steve O's answer and just add 2 hydroxide ions to both sides the hydrogen ions will be converted to water and you will get my answer.  So his answer and mine are equivalent in that sense, but your instructor asked you for basic balancing.