Give the important properties and uses of sodium carbonate.

Properties of sodium carbonate: It dissolves in water with evolution of heat. Its aqueous solution is alkaline due to hydrolysis and its solution turns red litmus blue.

Na₂CO₃(s) + H₂O(l) → 2NaOH(ag) + CO₂(g)

Upon cooling its hot concentrated solution, this gives Na₂CO₃ · 10H₂O (decahydrate). When this variety is exposed to air, it efflorescences and finally changes into monohydrate Na₂CO₃ · H₂O. Upon strong heating, this changes into anhydrous form. It reacts with mineral acids to give carbon dioxide gas.

Na₂CO₃(s) + 2HCl(aq) → 2NaCl(s) + CO₂(g) + H₂O(l).

Uses:
(i) It is used in the manufacture of glass, soap powder, caustic soda and borax.
(ii) It is employed as a base in acid base titrations.
(iii) It is used as washing soda in detergents.
(iv) It is used in the softening of water.