Question

What is the use of Clark’s method?

• A. Remove temporary hardness of water by adding quick lime or slaked lime.
• B. Remove permanent hardness by adding washing soda.
• C. Remove permanent hardness by adding permutit.
• D. Remove temporary hardness by boiling.

Answer 1

Answer: (A)

Temporary hardness in water is due to the presence of magnesium and calcium hydrogen carbonates.

Clark’s method: In this method, the calculated amount of lime is added to hard water. It precipitates out calcium carbonate and magnesium hydroxide which can be filtered off.

$Ca \left( HCO _{3}\right)_{2}+ Ca ( OH )_{2} \rightarrow 2 CaCO _{3} \downarrow+2 H _{2} O$

$Mg \left( HCO _{3}\right)_{2}+2 Ca ( OH )_{2} \rightarrow 2 CaCO _{3} \downarrow+ Mg ( OH )_{2} \downarrow$

$+2 H _{2} O$