Chapter : 1. Metals & Non Metals
Electrolytic reduction
(iii) Electrolytic reduction : The reactive metals (high up in the activity series) cannot be produced by any of the above methods. They are obtained by electrolytic reduction of their molten oxides or chlorides. During electrolysis, the cathode supplies electrons to metal ions for their reduction to the metal.
Examples :
(i) Sodium metal is obtained by the electrolysis of molten sodium chloride.
(ii) Magnesium metal is obtained by the electrolysis of molten magnesium.
(iii) Aluminium oxide (Al2O3) is reduced to aluminium by the electrolysis of molten aluminium oxide.
Al2O3 → 2Al3+ + 3O2–
The aluminium ions present in aluminium oxide go to the cathode and are reduced there to aluminium atoms.
Note : During electrolytic reduction of the molten salts, the metals are always liberated at the cathode.
(iv) Some specific methods Silver and gold are obtained by treating the ore with a solution of sodium cyanide. Sodium argentocyanide (in case of silver) or sodium aurocyanide (in case of gold) is obtained in the solution. On adding zinc dust to the solution, silver or gold is precipitated.
2Na[Ag(CN)2] + Zn → Na2[Zn(CN)4] + 2Ag
2Na[Au(CN)2] + Zn → Na[Zn(CN)4] + 2Au
Examples :
(i) Sodium metal is obtained by the electrolysis of molten sodium chloride.
(ii) Magnesium metal is obtained by the electrolysis of molten magnesium.
(iii) Aluminium oxide (Al2O3) is reduced to aluminium by the electrolysis of molten aluminium oxide.
Al2O3 → 2Al3+ + 3O2–
The aluminium ions present in aluminium oxide go to the cathode and are reduced there to aluminium atoms.
Note : During electrolytic reduction of the molten salts, the metals are always liberated at the cathode.
(iv) Some specific methods Silver and gold are obtained by treating the ore with a solution of sodium cyanide. Sodium argentocyanide (in case of silver) or sodium aurocyanide (in case of gold) is obtained in the solution. On adding zinc dust to the solution, silver or gold is precipitated.
2Na[Ag(CN)2] + Zn → Na2[Zn(CN)4] + 2Ag
2Na[Au(CN)2] + Zn → Na[Zn(CN)4] + 2Au
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