Ncert Exercises & Solutions

Given below are two statements:

Assertion (A):	Permanent hardness of water is removed by treatment with washing soda.
Reason (R):	Washing soda reacts with soluble magnesium and calcium sulphate to form insoluble carbonates.

1.	Both (A) and (R) are true and (R) is the correct explanation of (A).
2.	Both (A) and (R) are true but (R) is not the correct explanation of (A).
3.	(A) is true but (R) is false.
4.	(A) is false but (R) is true.

Hint: Permanent hardness is due to the presence of soluble salts of magnesium and calcium in the form of chlorides and sulphates in water.

Washing soda reacts with soluble calcium and magnesium chlorides and sulphates in hard water to form insoluble
carbonates.

The reaction is as follows:

{Na}_{2} {CO}_{3} + \underset{or {CaSO}_{4}}{{MgSO}_{4}}

(from hard water) \to {Na}_{2} {SO}_{4} + \underset{or {CaCO}_{3}}{{MgCO}_{3}}

(insoluble)