Question

Soaps do not work in hard water containing calcium and magnesium ions because

• A. $C{a}^{2+}$ and $M{g}^{2+}$ ions form insoluble calcium and magnesium salts in the form of scum
• B. $N{a}^{+}$ and $K^{+}$ present in soap react with $C{a}^{2+}$ and $M{g}^{2+}$ and hinder cleansing process
• C. a large amount of soap is to be used in presence of $C{a}^{2+}$ and $M{g}^{2+}$
• D. scum formed by combination of $N{a}^{+},C{a}^{2+}$ and $M{g}^{2+}$ stick to the cloth and are not removed on agitation

Answer 1

Answer: (A)

$C{a}^{2+}$ and $M{g}^{2+}$ ions form insoluble calcium and magnesium soaps respectively when sodium or potassium soaps are dissolved in hard water.
$\underset{\text{Soap}}{2C_{17}{H}_{35}COOHNa}+CaC{l}_2\to 2NaCl+\underset{\text{Insoluble calcium stearate (soap) }}{(C_{17}{H}_{35}COO{)}_{2}Ca}$
These insoluble soaps separate as scum in water and are useless as cleansing agent.