Question

The method used to remove temporary hardness of water is:

• A. Synthetic resins method
• B. Calgon's method
• C. Clark's method
• D. Ion - exchange method

Answer 1

The correct option is C Clark's method

Temporary hardness is a type of water hardness caused by the presence of dissolved bicarbonate minerals (calcium bicarbonate and magnesium bicarbonate). The presence of the metal cations makes the water hard. However, unlike the permanent hardness caused by sulphate and chloride compounds, this "temporary" hardness can be reduced by boiling the water.

Water softening by Clarke’s process uses calcium hydroxide (lime). It removes temporary hardness.

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

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.