Sodium hydroxide (caustic soda) NaOH

Sodium hydroxide, caustic soda, NaOH, is manufactured commercially by electrolysing a saturated aqueous solution of sodium chloride (brine) in a Castner-Kellner cell, which uses a mercury cathode and a carbon-rod anode. At the mercury cathode, Na⁺ ions are reduced and the sodium metal produced dissolves in the mercury to form a sodium amalgam, Na⁺ + e⁻ →(Hg) Na-amalgam; at the carbon anode, chloride ion is oxidised and chlorine gas evolves, Cl⁻ → ½Cl2 + e⁻. The sodium amalgam is then treated with water, which liberates hydrogen gas and yields sodium hydroxide: 2Na-Hg + 2H2O → 2NaOH + 2Hg + H2.

Properties: sodium hydroxide is a white, deliquescent solid with a melting point of 591 K; it is highly soluble in water and gives a strongly alkaline solution. Left exposed, the surface of an NaOH solution absorbs atmospheric CO2 and slowly converts to Na2CO3. …