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.


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.

CO2-3  +  H2O   →   HCO-3  +  OH-


  • 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.