Sodium Carbonate, Na2CO3.10H2O

Sodium Carbonate,  Na₂CO₃.10H₂O

Sodium carbonate or Washing Soda is generally prepared by Solvay process. In this process, advantage is taken of the low solubility of sodium hydrogencarbonate whereby it gets precipitated in the reaction of sodium chloride with ammonium hydrogencarbonate. The latter is prepared by passing CO₂ to a concentrated solution of sodium chloride satrated with ammonia, where ammonium carbonates followed by ammonium hydrogencarbonate are formed. The equations for the complete process may be written as:

2NH₃  +  H₂O  +  CO₂   →   (NH₄)₂CO₃

(NH₄)₂CO₃  +  H₂O  +CO₂   →   2NH₄HCO₃

NH₄HCO₃  +  NaCl   →  NH₄Cl  +  NaHCO₃

sodium hydrogencarbonate crystal separates. These are heated to give sodium carbonate.

2NaHCO₃   →   Na₂CO₃  +  CO₂  +  H₂O

In this process NH₃ is recovered when the solution containing NH₄Cl is treated with Ca(OH)2. Calcium chloride is obtained as a by-product.

2NH₄Cl  +  Ca(OH)₂   →  2NH₃  +  CaCl₂  +  H₂O

It may be mentioned here hat Solvay process cannot be extended to the manufacture of potassium carbonate because potassium hydrogencarboate is too soluble to be precipitated by the additional of ammonium hydrogencarbonate to a saturated solution of potassium chloride.

Properties

Sodium carbonate is a white crystalline solid which exists as a decahydrate, Na₂CO₃.10H₂O. This is also called washing Soda. It is readily soluble in water. On heating, the decahydrate loses is water of crystallization to form monohydrate. About 373K, the monohydrate becomes completely anhydrous and changes to a white powder called soda ash.

Carbonate part of sodium carbonate gets hydrolysed by water to form an alkaline solution.

CO^2-₃  +  H₂O   →   HCO^-₃  +  OH^-

Uses

• It is used in water softening, laundering and cleaning.
• It is used in the manufacture of glass, sap, borax and caustic soda.
• It is used in paper, paints and textile industries.
• It is an important laboratory regent both n qualitative and quantitative analysis.