Sodium hydroxide is generally prepared commercially by the electrolysis of sodium chloride in Castner-Kellner cell. A brine solution is electrolyzed using mercury cathode and carbon (graphite rod) anode. Sodium metal, discharged at the cathode, combines with mercury to form sodium amalgam. Chlorine gas is evolved at the anode.
The amalgam is treated with water to give sodium hydroxide and hydrogen gas.
Properties :
i) Sodium hydroxide is while, translucent solid.
ii) It melts at 591K.
iii) It is readily soluble in water and forms a strong alkaline solution.
iv) The solution of sodium hydroxide at the surface reacts with CO2 in the atmosphere to form Na2CO3.
Uses :
i) It is useful in purification of bauxite.
ii) It is used in the manufacture of soap, paper, artificial silk and a number of chemicals.
iii) It is useful in petroleum refining.
iv) Also used in the textile industries for mercerizing cotton fabrics.
v) It is important as laboratory reagent.
vi) It is useful in preparation of pure fats and oils.