Sodium carbonate: Manufacture, properties and uses

Sodium carbonate exists as anhydrous (Na₂CO₃) and also as hydrated salt. The decahydrated salt (Na₂CO₃.10H₂O) is known as washing soda while the anhydrous salt is called soda ash. It occurs native as Na₂CO₃.NaHCO₃.H₂O) in Egypt, and as 'Reh' and 'Sajji' in several districts of Uttar Pradesh and Bihar.During hot weather, soda is also collected from a large number of alkaline lakes or dhands in East Sind and the Pakistan State of Khairpur.

Manufacture of Sodium Carbonate

Sodium carbonate is usually made by the Ammonia-soda process or Solvay process. The raw materials for this process are common salt, ammonia and limestone (for supplying CO₂ and quicklime).

When carbon dioxide is passed into a concentrated solution of brine saturated with ammonia, ammonium bicarbonate is produced. The ammonium bicarbonate then reacts with common salt forming sodium bicarbonate.

Sodium bicarbonate being slightly soluble (in presence of sodium ions) gets precipitated. Precipitated sodium bicarbonate is removed by filtration and changed into sodium carbonate by heating.

Properties

Sodium carbonate is a white crystalline solid, which can exists as anhydrous salt (Na₂CO₃), monohydrate salt (Na₂CO₃.H₂O), heptahydrate salt (Na₂CO₃.7H₂O) and decahydrate (Na₂CO₃.10H₂O - washing soda). Sodium carbonate is readily soluble in water. On heating, the decahydrate salt gradually loses water to, finally give anhydrous salt (Na₂CO₃ - soda ash).

Uses

• For the manufacture of glass
• For washing purposes in laundries
• For the manufacture of other sodium compounds like sodium silicates, sodium hydroxide, borax, hypo etc.
• As a household cleansing agent
• In paper and soap/detergent industries
• For the softening of water
• A mixture of NaCO₃ and KCO₃ is used as a fusion mixture
• In textile industry and petroleum refining