Question

If excess of $Ca(OH{)}_2$ is added to hard water in clark’s method.

• A. Temporary hardness is not removed
• B. Permanent hardness is removed
• C. Temporary hardness occurs
• D. Permanent hardness occurs

Answer 1

Answer: (D)

Temporary hardness is not removed

Clark’s method to remove the hardness of water

In Clark’s water softening method, hard water is treated with $Ca{\left(OH\right)}_2$ (slaked lime). Calcium hydroxide is Clark’s reagent. It removes the hardness of water by converting bicarbonates into carbonate. Water softening by Clarke’s process uses calcium hydroxide (lime). It removes temporary hardness.

Reaction

$Ca{\left(HC{O}_3\right)}_2+Ca{\left(OH\right)}_2⟶2CaC{O}_3+2H_{2}O$

This method involves the addition of slaked lime to water either in solid or in liquid form. This results in the conversion of soluble bicarbonates to insoluble carbonates.

If an excess of $Ca(OH{)}_2$ is added, Temporary hardness is not removed due to the formation of calcium bicarbonate.

$2CaC{O}_3+Ca{\left(OH\right)}_2⟶2Ca{\left(HC{O}_3\right)}_2+2H_{2}O$