Sodium hydroxide is prepared commercially by the electrolysis of brine solution in Castner-Kellner cell using a mercury cathode and a carbon anode. Sodium metal is discharged at the cathode and combines with mercury to form sodium amalgam. Chlorine gas is evolved at the anode. The sodium amalgam thus obtained is treated with water to give sodium hydroxide.
At cathode : Na+ + e– → Na(amalgam)
At anode : Cl– → ½ Cl2 ↑+ e–
Sodium hydroxide is a white, translucent and deliquescent solid, that dissolves in water to give a strong alkaline solution. It melts at 591 K. The sodium hydroxide solution at the surface reacts with the CO2 in the atmosphere to form Na2CO3
· Sodium hydroxide is used as a laboratory reagent
· It is also used in the purification of bauxite and petroleum refining
· It is used in the textile industries for mercerising cotton fabrics
· It is used in the manufacture of soap, paper, artificial silk and a number of chemicals