Ncert Exercises & Solutions

Assertion: Permanent hardness of water is removed by treatment with washing soda.

Reason: Washing soda reacts with soluble magnesium and calcium sulphate to form insoluble carbonates.

1. Both assertion and reason are true and the reason is the correct explanation of assertion.

2. Both assertion and reason are true and the reason is not the correct explanation of assertion.

3. Assertion is true but the reason is false.

4. Assertion is false but the reason 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} (from hard water)}{{MgSO}_{4}} \to {Na}_{2} {SO}_{4} + \underset{or {CaCO}_{3} (insoluble)}{{MgCO}_{3}}