Hardness can be defined as "the soap consuming capacity of water simple" OR it prevents the lathering of soap.

eg. $2c_{17}H_{35}COONa+ CaCl_{2}\rightarrow Ca[C_{17}H_{35}COO]_{2}\downarrow +2NaCl$

Sodium stearate Hardness Calcium stearate

Soluble soap Insoluble soap

ie. Long chain fatty acids.

$2c_{15}COOk+CaCl_{2}\rightarrow Ca[C_{17}H_{35}COO]_{2}\downarrow +2KCl$

$Potasium linolate \ \ \ \ \ Hardness \ \ \ \ \ Calcium linolate$

Soluble soap

ie. Long chain fatty acids.