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The extraction of Au by leaching with NaCN involves both oxidation and reduction. Justify giving equation.

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  • 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.

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