Question

Soaps do not work with 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 hinder the 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 the combination of $N{a}^{+},C{a}^{2+}$ and $M{g}^{2+}$ stick to the cloth and are not removed on agitation

Answer 1

The correct option is A $C{a}^{2+}$ and $M{g}^{2+}$ ions form insoluble calcium and magnesium salts in the form of scum

$C{a}^{2+}$and $M{g}^{2+}$ ions insoluble calcium and magnesium soaps respectinely when sodium or potassium soaps are dissolved in hard water.
${}^7{C}_{17}{H}_{15}COONa+CaC{l}_2\to 2NaCl+(C_{17}{H}_{35}COO{)}_{2}Ca$
Soap Insoluble calcium stearate (soap)
These insoluble soaps separate as scum in water and are useless as cleaning agents.