Question

Water which gives lather with soap easily is called hard water.
A.True
B.False

Answer 1

Hard water is defined based on how much of the dissolved calcium, and magnesium as minerals are there in it. Soaps are sodium or potassium salts of fatty acids. Soaps when treated with water undergo a reaction with the water minerals and give lather according to the nature of the water.

Complete step by step answer:
(1) There are two varieties of water, soft water, and hard water. Hard water contains salts of magnesium, and calcium with bicarbonates, sulphates, and chlorides. Sometimes, ferrous ions may also be present which is further oxidized to ferric form which is seen as a reddish-brown stain on the washed fabrics.
(2) Calcium carbonate causes temporary hardness of water, but other salts like sulphates, and chloride cause permanent hardness of water.
(3) The magnesium or calcium ions present in the hard water replaces the sodium or potassium ions present in the soap molecules (composed of fatty acids) and undergo a reaction to form an insoluble gelatinous curd-like substance called the scum. This reaction prevents the formation of lather with soap easily in case of hard water. So, water which gives lather with soap easily is not hard water but is called soft water.
Hence, option (B) is correct, the given statement is false.

Additional information:
The cleansing action of the soaps, and detergents is governed by their structures. They have the ability to lower the surface tension of water, for emulsification of oil or grease, and for holding them in a suspension in water.

Note: The cleansing action of detergent is better than soap. Soap contains carboxylate whereas detergents contain polar sulfonates, which are more soluble in hard water, and gives more lather unlike soaps.