Preparation of sodium carbonate by solvay process:- Sodium carbonate is generally prepared by Solvay process. In this process, Brine (NaCl solution) is converted to sodium carbonate. Common salt and lime stone are used as raw material. The main steps of the process are :
1. In this process advantage is taken of the low solubility of sodium hydrogen Carbonate whereby it gets precipitated in the reaction of sodium chloride with ammonium hydrogen carbonate. The latter is prepared by passing CO2 to a concentrated solution of sodium chloride saturated with ammonia, where ammonium carbonate followed by ammonium hydrogen carbonate are formed. The equations for the complete process may be written as
2NH3 + H2O + CO2 ➝ (NH4)2 CO3
(NH4)2 CO3 + H2O + CO2 ➝ 2NH4HCO3
NH4HCO3 +NaCl ➝ NH4Cl +NaHCO3
Sodium hydrogen carbonate is insoluble due to common ion effect. It can be obtained by filtration.
2. Sodium hydrogen carbonate crystal separates. These are heated at 1500°C to given sodium carbonate.
2NaHCO3 ➝ Na2CO3 + CO2 + H2O
3. In this process NH3 solution containing NH4Cl is treated with Ca (OH)2. Calcium chloride is obtained as a by-product.
CaCO3 ➝ CaO + CO2
CaO + H2O ➝ Ca(OH)2
2NH4Cl + Ca(OH)2 ➝ 2NH3 + CaCl3 + 2H2O
It may be mentioned here that solvay process cannot be extended to the manufacture of potassium carbonate because potassium hydrogen carbonate is to soluble to be precipitated by the addition of ammonium hydrogen carbonate to a saturated solution of potassium chloride.
