Sodium carbonate is generally prepared by Solvay process. This process is also known as ammonia soda process. Raw materials are NaCl, milk of lime and ammonia. In this process, CO
2 is bubbled through the solution of brine ( NaCl ) saturated with ammonia when sodium hydrogen carbonate precipitates due to common ion effect.
NH3 + H2O + CO2 → NH4HCO3
Ammonium hydrogen carbonate
NaCl + NH4HCO3 → NaHCO3↓ + NH4Cl
It is filtered and then ignited to get sodium carbonate.
2NaHCO3 → Na2CO3 + CO2 + H2O
NH4Cl obtained in the above reaction is treated with milk of lime to recover NH3 and a valuable by product CaCl2 is obtained.
2NH4Cl + Ca(OH)2 → CaCl2 + 2H2O + 2NH3
Potassium carbonate, however cannot be obtained by this process because potassium hydrogen carbonate being highly soluble in water cannot be precipitated.
Properties Na2CO3
Sodium Carbonate crystallizes from water as a deca hydrate, Na2CO3 . 10H2O.
This is also called washing soda. It is readily soluble in water. On heating the decahydrate losses water of crystallization to form monohydrate. Above 373K, the monohydrate becomes completely anhydrous and changes to a white powder called soda ash.
CO2 of sodium carbonate gets hydrolysed by water to form an alkaline solution,
On passing CO2 through aqueous solution, sodium hydrogen carbonate is formed.
Na2CO3 + H2O + CO2 → 2NaHCO3
Uses Of Na2CO3
i) It is used in the manufacture of glass, soap borax and caustic soda.
ii) It is used in water softening in laundry and cleaning.
iii) It is important reagent both in qualitative and quantitative analysis.
iv) It is used in paper, paints and textile industries.
