Q. 44 Note
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Theextraction of gold and silver involves leaching the metal with CN–. This is also an oxidation reaction (Ag → Ag+ or Au → Au+). The metal is later recovered by displacement method.MacArthur-Forrest process of gold cyanidation takes place as follows
4Au(s) + 8CN– (aq) + 2H2O(aq) + O2(g) → 4[Au(CN)2] – (aq) + 4OH– (aq)
2[Au(CN)2] – (aq) + Zn(s) → 2Au(s) + [Zn(CN)4] 2– (aq)
Zinc places the role of a reducing agent. It reduces Au+ to pure Au.
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