Water — Question 10

If the water is hard, calcium and magnesium ions of the water combine with the negative ions of the soap to form a slimy precipitate of insoluble calcium and magnesium usually called soap curd (scum).

$\underset{\text{[soap]}}{2\text{NaSt}} + {\text{Ca(HCO}_3)_2} \longrightarrow \underset{\text{[soap curd]}}{\text{CaSt}_2} ↓ + {2\text{NaHCO}_3}$

${2\text{NaSt}} + {\text{Mg(HCO}_3)_2} \longrightarrow {\text{MgSt}_2} ↓ + {2\text{NaHCO}_3}$

In permanent hard water, the formation of soap- curd will go on as long as there are calcium and magnesium ions present.

${2\text{NaSt}} + {\text{CaCl}_2} {\longrightarrow} {\text{CaSt}_2} ↓ + {2\text{NaCl}}$

${2\text{NaSt}} + {\text{MgCl}_2} {\longrightarrow} {\text{MgSt}_2} ↓ + {2\text{NaCl}}$

${2\text{NaSt}} + {\text{CaSO}_4} {\longrightarrow} {\text{CaSt}_2} ↓ + {2\text{Na}_2{\text{SO}_4}}$

${2\text{NaSt}} + {\text{MgSO}_4} {\longrightarrow} {\text{MgSt}_2} ↓ + {2\text{Na}_2{\text{SO}_4}}$

As long as the formation of soap-curd continues, no soap lather will be formed and the cleaning of cloth or body will not be possible.