Explain with equation, what is noticed when permanent hard water is treated with

(a) slaked lime

(b) washing soda

(a) Permanent hardness due to magnesium salts can be partly removed by slaked lime because magnesium ions form insoluble magnesium hydroxide.

MgSO₄ + Na₂CO₃ + Ca(OH)₂ ⟶ Mg(OH)₂ ↓ + CaCO₃ ↓ + Na₂SO₄

However, this alone does not completely soften water because calcium sulphate remains in solution. Washing soda is required for complete removal of permanent hardness.

(b) Washing soda is added to hard water, which results in settling down of insoluble carbonates which can be removed by filtration.

$\underset{\text{Washing soda}}{\text{Na}$2\text{CO}3} + \underset{\text{Calcium sulphate}}{\text{CaSO}4} \longrightarrow \underset{\text{Calcium carbonate}}{\text{CaCO}3↓} + \text{Na}2\text{SO}4

$\underset{\text{Washing soda}}{\text{Na}$2\text{CO}3} + \underset{\text{Calcium chloride}}{\text{CaCl}2} \longrightarrow \underset{\text{Calcium carbonate}}{\text{CaCO}3↓} + 2\text{NaCl}