In Solvay process, CO2 is passed through brine saturated with ammonia .when NaHCO3 being sparingly soluble gets precipitated.
NaCl + NH3 + CO2 -------> NaHCO3 + NH4Cl -----(i)
Sodium bicarbonate thus formed is filtered, dried and then heated when sodium carbonate is Obtained.
2 NaHCO3 ------> Na2CO3 + CO2 + H2O CO2 needed for the reaction shown in eq.(i) is prepared by heating calcium carbonate and the quick lime, CaO thus formed is dissolved in water to form slaked lime, Ca(OH)2 . NH3 needed for the purpose is prepared by heating NH4Cl.