Question

Temporary hardness of water is removed in Clark's process by adding:

• A. Lime
• B. Borax
• C. Calgon
• D. Caustic soda

Answer 1

The correct option is A

Lime

Explanation for correct answer:-

Option (A) Lime

• Temporary hardness of water is caused due to the presence of bicarbonates of magnesium and calcium.
• Clark's process is used to remove the temporary hardness of water by adding lime to it which converts the bicarbonates into carbonates.
• The reaction of Clark’s process:

$\underset{\left(\mathrm{Bicarbonate}\right)}{\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2(\mathrm{aq}.)}+\underset{\left(\mathrm{Lime}\right)}{\mathrm{Ca}{\left(\mathrm{OH}\right)}_2(\mathrm{aq}.)}\to \underset{\left(\mathrm{Carbonate}\right)}{2{\mathrm{CaCO}}_3}\left(\mathrm{s}\right)+\underset{\left(\mathrm{Water}\right)}{2{\mathrm{H}}_2\mathrm{O}}\left(\mathrm{l}\right)$

Explanation for Incorrect answers:-

Option (B)Borax

• It acts as a softening agent for hard water.
• However, it is not used in Clark's process.

Option (C)Calgon

• It is used to remove the permanent hardness of the water.
• It is not used in Clark's process.

Option (D) Caustic soda

• It can be used to remove the hardness of water but it is not used in Clark's process.

Hence, option A is correct.