Why do calcium ions makes water hard but sodium ion does not?

Question

Why do calcium ions makes water hard but sodium ion does not? (A) Calcium forms insoluble compound with stearate ion present in soap (B) Sodium forms insoluble compound with stearate ion present in soap (C) Calcium forms soluble compound with stearate ion present in soap (D) Both calcium and sodium forms insoluble compound with stearate ion present in soap

Tardigrade Admin · Accepted Answer

Soaps are sodium or potassium salts of higher fatty acids, eg, sodium stearate. Sodium stearate or sodium and potassium salts of higher fatty acids are water soluble but the corresponding magnesium and calcium salts are not. Thus, these make water hard.

Q. Why do calcium ions makes water hard but sodium ion does not?

Calcium forms insoluble compound with stearate ion present in soap

Sodium forms insoluble compound with stearate ion present in soap

Calcium forms soluble compound with stearate ion present in soap

Both calcium and sodium forms insoluble compound with stearate ion present in soap

Soaps are sodium or potassium salts of higher fatty acids, eg, sodium stearate. Sodium stearate or sodium and potassium salts of higher fatty acids are water soluble but the corresponding magnesium and calcium salts are not. Thus, these make water hard.