Question

Temporary and permanent hardness of water can be removed by:-

• A.
• B. Scum formed by lathering soap
• C. Dilute
• D. Zn-Cu couple

Answer 1

The correct option is D

Zn-Cu couple

Temporary hardness of water is due to the presence of dissolved bicarbonates of calcium and magnesium. This can be removed by boiling or addition of calcium hydroxide ${\text{Ca(OH)}}_2$.

Permanent hardness of water is due the presence of dissolved sulphates and chlorides of magnesium and calcium. This can be removed by addition of washing soda $\left({\text{Na}}_2{\text{CO}}_3\right)$.