Question

Permanent hardness of water is due to the presence of chlorides and salts of calcium and magnesium. It can be removed by using .

• A. caustic soda
• B. washing soda
• C. sulphates
• D. bicarbonates

Answer 1

Answer: (B), (C)

The correct options are
B washing soda
C sulphates

The permanent hardness of water is due to the dissolved chlorides and sulphates of magnesium and calcium.
One of the method to remove it is by treating the hard water with washing soda, i.e., $N{a}_{2}C{O}_3$.
This forms their respective insoluble carbonates which are removed by filtration.
The reactions involved are:

${\text{Na}}_2{\text{CO}}_3\text{(s)}+{\text{CaSO}}_4\text{(aq)}\to {\text{CaCO}}_3(\downarrow )+{\text{Na}}_2{\text{SO}}_4\text{(aq)}$

${\text{Na}}_2{\text{CO}}_3\text{(s)}+{\text{MgCl}}_2\text{(aq)}\to {\text{MgCO}}_3(\downarrow )+\text{2NaCl(aq)}$