Question

Water is said to be permanently hard when it contains:

• A. Chloride and sulphates of Mg and Ca.
• B. Birrbonates of Na and K.
• C. Carbonates of Na and K.
• D. Phosphate of Na and K

Answer 1

The correct option is A Chloride and sulphates of Mg and Ca.

Permanent hardness of water is due to sulfates and chlorides of calcium and magnesium. Temporary hardness of water is due to bicarbonates of calcium and magnesium.

Theory :
Summary:
Cause of hardness of water:
Due to presence of bicarbonates, chlorides and sulphates of calcium and magnesium
The cations $\left(C{a}^{2+}andM{g}^{2+}\right)$ present in hard water react with soap to form insoluble precipitates.
$\underset{\text{From hard water}}{M^{2+}}+\underset{\text{Sodium stearate (soap)}}{2C_{17}{H}_{35}COONa}\to \underset{\text{Metal stearate(PPt.)}}{(C_{17}{H}_{35}COO{)}_{2}M\downarrow }+2N{a}^{+}$
Where M= Ca or Mg
No lather is produced until all the calcium and magnesium ions are precipitated. This also results in the wastage of a lot of soap.
Types of hardness of water:
Temporary hardness: It is due to the presence of bicarbonates of calcium and magnesium. It is also called carbonate hardness.
Permanent hardness: It is due to the presence of chlorides and sulphates of calcium and magnesium. It is also called non-carbonate hardness.