Temporary hard water is formed when rain water containing dissolved carbon(IV) oxide flows over deposits of?

A. CaCO3
B. Na2CO3
C. Na2SO4
D. CaSO4

Correct Answer:

Option A – CaCO3

Explanation

Permanent hardness in water= Mg and Ca Sulphate.
Temporary hardness in water= Mg and Ca Carbonate.

Temporary hardness of water is caused by Magnesium and calcium hydrogencarbonate. It is formed when rainwater containing dissolved CO2 flows over a deposit of CaCO3

i.e CaCO3 + CO2 + H2O → Ca(HCO3)2