Question

Name the following:

(i) The scum is formed when permanent hard water containing magnesium ions reacts with soap.

(ii) A sodium salt that removes both temporary and permanent hardness.

(iii) The organic acid whose sodium salt is the constituent of soap.

Answer 1

(i) The scum is formed when permanent hard water containing magnesium ions reacts with soap.

Hard water contains calcium$\left({\mathrm{Ca}}^{+2}\right)$ and magnesium$\left({\mathrm{Mg}}^{+2}\right)$ ions. When soap comes in touch with water, these ions form calcium and magnesium salts of fatty acids which are insoluble in water. These calcium or magnesium salts precipitate out in the form of scum. The scum formed is Magnesium stearate$\left[\mathrm{Mg}{\left({\mathrm{C}}_{18}{\mathrm{H}}_{35}{\mathrm{O}}_2\right)}_2\right]$.

(ii) A sodium salt that removes both temporary and permanent hardness.

Sodium carbonate $\left({\mathrm{Na}}_2{\mathrm{CO}}_3\right)$ is additionally referred to as sodium carbonate. It can remove temporary and permanent hardness from the water.

(iii) The organic acid whose sodium salt is the constituent of soap.

Sodium stearate${\mathrm{C}}_{18}{\mathrm{H}}_{35}{\mathrm{NaO}}_2$ is the sodium salt of stearic acid. This white solid is the most common soap.