- 4Au (s) + 8CN- (aq) + 2H2O2 (aq) + O2 (g) → 4[Au(CN)2]- (aq) + 4OH- (aq)
- 2[Au(CN)2]- (aq) + Zn(s) → 2Au(s)+ [Zn(CN)4]-2 (aq)
In the first reaction Au changes into Au+ , i.e. its oxidation takes place. In the second reaction:
Au+ → Au°
(i.e.) reduction takes place.