Question

The hard water of a well becomes soft on adding washing soda to it.

Answer 1

The hardness of hard water is due to the presence of chlorides and sulphates of calcium and magnesium. When washing soda (Na₂CO₃. 10H₂O) is added to the hard water, Na₂CO₃ reacts with the chlorides and sulphates of calcium and magnesium and converts them to insoluble carbonate salts. This changes the hard water into soft water and thus makes it suitable for use.

MgCl2 (aq)+ Na2CO3 (s) - MgCO3(s) + 2 NaCl (s)