Sodium Hydroxide (NaOH)

Sodium Hydroxide (NaOH)

Sodium hydroxide or Caustic Soda is generally prepared commercially by the electrolysis of sodium chloride in Castner-Kellner cell. A brine solution is electrolysed using a mercury cathode and a carbon 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.

 2Na-amalgam  +  2H₂O →  2NaOH  +  2Hg  +  H₂

Sodium hydroxide is a white, translucent solid. It melts at 591 K. It is readily soluble in water to give a strong alkaline solution. Crystals of sodium hydroxide are deliquescent. The sodium hydroxide solution at the surface reacts with the CO₂ in the stmosphere to form Na₂CO₃.

Uses

It is used in

• The manufacture of soap, paper, artificial silk and number of chemicals.
• In petroleum refining
• In the purification of bauxite.
• In the textile industries for mercerizing cotton fabrics,
• For the preparation of pure fats and oils
• As a laboratory reagent.