Why soaps do not work in hard water?

Explanation

Soaps are sodium or potassium salts of long-chain falty acids. Hard water contains calcium and magnesium ions. When soaps are dissolved in hard water, these ions displace sodium or potassium from insoluble calcium or magnesium salts of fatty acids. These insoluble salts separate as scum.
`" "underset(("Soap"))(2C_(17)H_(35)COONa)+CaCl_(2) rarr 2NaCl+underset("Insoluble (calcium stearate)")((C_(17)H_(35)COO)_(2)Ca)`
This is the reason why soaps do not work in hard water.