Hydrogen
8.0 Hard and Soft Water
8.0 Hard and Soft Water
Depending upon the behaviour of water towards soap solution, water may be classified as Hard and Soft water. Being a good solvent, when it flows on the surface of the earth, it dissolves many salts. Presence of calcium and magnesium salts in the form of hydrogencarbonate, chloride and sulphate in water makes water 'hard'.
Hard water does not give lather with soap. Hard water forms scum/precipitate with soap. Soap containing sodium stearate $(C_{17}H_{35}COONa)$ reacts with hard water to precipitate out $Ca/Mg$ stearate.
$$2{C_{17}}{H_{35}}COONa\left( {aq} \right) + {M^{2 + }}\left( {aq} \right) \to {({C_{17}}{H_{35}}COO)_2}M + 2N{a^ + }\left( {aq} \right);{\text{ }}M{\text{ is }}Ca/Mg$$
It is, therefore, unsuitable for laundry. It is harmful for boilers as well, because of deposition of salts in the form of scale. This reduces the efficiency of the boiler.
Water free from soluble salts of calcium and magnesium is called Soft water. It gives lather with soap easily.
The hardness of water may be
(a) Temporary Hardness: due to presence of bicarbonates of calcium and magnesium.
(b) Permanent Hardness: due to sulphates or chlorides of calcium and magnesium.
