By the addition of washing soda, we can remove both temporary as well as permanent hardness from water. Bicarbonate salts as well as sulphate and chloride salts undergo double decomposition reaction with sodium carbonate. In these reactions, the insoluble carbonates formed get precipitated and are removed by filtration.
`Ca(HCO_(3))_(2)+NaCO_(3)rarrCaCO_(3)darr+2NaHCO_(3)`
`MgSO_(4)+Na_(2)CO_(3)rarrCaCO_(3)darr+2NaCl`
`CaCl_(2) + Na_(2)CO_(3) rarr CaCO_(3) darr + 2NaCl`
`CaCl_(2) + Na_(2)CO_(3) rarr CaCO_(3) darr + 2NaCl`
