Preparation of sodium hydroxide
Sodium hydroxide is industrially produced as a 50 per cent solution by variations of the electrolytic chloralkali process. Chlorine gas is also produced in this process. Solid sodium hydroxide is obtained from this solution by the evaporation of water.
Various methods of preparation of sodium hydroxide are -
Castner — Kellener Process
Principle — In castner-kellner method NaOH is prepared by the electrolysis of aqueous solution of NaCl (Brine).
Castner-kellner cell — It is a rectangular tank of steel. Inside of tank is lined with ‘ebonite.’ Anode is made of titanium. Flowing layer of mercury (Hg) at the bottom of tank serves as cathode.
When electric current is passed through brine, +ve and -ve ions migrate towards their respective electrodes. Na+ ions are discharged at mercury cathode. The sodium deposited at mercury forms Sodium Amalgam. Chlorine produced at the anode is removed from the top of the cell.
reaction at cathode
Na+ ions are discharged in preference to H+ ions due to high over voltage.
Reaction at anode
Formation of NaOH
Amalgam moves to another chamber called ‘denuder,’ where it is treated with water to produce NaOH which is in liquid state. Solid NaOH is obtained by the evaporation of this solution.
NaOH obtained is highly pure and the process is very effeicient.
Sodium hydroxide is industrially produced as a 50 per cent solution by variations of the electrolytic chloralkali process. Chlorine gas is also produced in this process. Solid sodium hydroxide is obtained from this solution by the evaporation of water.
Various methods of preparation of sodium hydroxide are -
Castner — Kellener Process
Principle — In castner-kellner method NaOH is prepared by the electrolysis of aqueous solution of NaCl (Brine).
Castner-kellner cell — It is a rectangular tank of steel. Inside of tank is lined with ‘ebonite.’ Anode is made of titanium. Flowing layer of mercury (Hg) at the bottom of tank serves as cathode.
When electric current is passed through brine, +ve and -ve ions migrate towards their respective electrodes. Na+ ions are discharged at mercury cathode. The sodium deposited at mercury forms Sodium Amalgam. Chlorine produced at the anode is removed from the top of the cell.
reaction at cathode
Na+ ions are discharged in preference to H+ ions due to high over voltage.
Reaction at anode
Formation of NaOH
Amalgam moves to another chamber called ‘denuder,’ where it is treated with water to produce NaOH which is in liquid state. Solid NaOH is obtained by the evaporation of this solution.
NaOH obtained is highly pure and the process is very effeicient.
