In Solvay ammonia process , `CO_(2)` is passed through brine , (i.e., a concentrated solution of NaCl) saturated with ammonia when sodium bicarbonate being sparingly soluble gets precipitated .
`NaCl + NH_(3) +CO_(2) + H_(2)O to NaHCO_(3) darr + NH_(4)Cl " " ... (i) `
Sodium bicarbonate thus formed is filtered , dried and then heated when sodium carbonate is obtained .
`2NaHCO_(3) overset(Delta)(to) Na_(2)CO_(3) + CO_(2) + H_(2)O`
`CO_(2)` 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)`
`CaCO_(3) overset(Delta)(to) CaO + CO_(2) " " ... (ii) `
`CaO + H_(2)O to Ca(OH)_(2) " " ... (iii)`
`NH_(3)` needed for the purpose is prepared by heating `NH_(4)Cl` obtained in Eq. (i) with `Ca(OH)_(2)` obtained in Eq. (iii)
`2NH_(4)Cl + Ca(OH)_(2) to 2NH_(3) + CaCl_(2) + 2H_(2)O`
Therefore , the only by product of the reaction is calcium chloride , `CaCl_(2)`.
