Question

calcium bicarbonate causes hardness in water but not calcium carbonate. why

Answer 1

calcium carbonate dissolve in water to form calcium hydroxide + carbon dioxide .but calcium bicarbonate is one of the salt that is present in hard water

hope it helps you

Answer 2

Calcium bicarbonate is sparingly soluble in water so it causes temporary hardness
but calcium carbonate is almost insoluble in water so it does not cause hardness.
Hardness is caused mainly by sparingly soluble bicarbonates,sulfates and chlorides of Mg and Ca