Question

Temporary hardness of water is caused by:

• A. calcium and magnesium chloride
• B. calcium and magnesium bicarbonate
• C. calcium and magnesium sulphate
• D. all of these

Answer 1

The correct option is B

calcium and magnesium bicarbonate

The explanation for the correct option: Option (B)

The hardness of water:

• The amount of dissolved calcium and magnesium salt in the water is called hard water.
• It is classified into two parts (i). Temporary hard water and (ii). Permanent hard water.

Temporary hardness:

• Temporary hardness is caused due to the presence of dissolved Calcium and Magnesium Bicarbonate $\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2\mathrm{and}\mathrm{Mg}{\left({\mathrm{HCO}}_3\right)}_2$ salts in water.

Removal of the temporary hardness of water:

• Clark's method is a process for the large-scale removal of temporary hardness from water.
• $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$is used as Clark’s reagent. It removes the hardness of water by converting Bicarbonates$\left({{\mathrm{HCO}}_3}^{-}\right)$ into Carbonates $\left({{\mathrm{CO}}_3}^{2-}\right)$.

Therefore, Option (B) is correct.