Question

Hard soaps are
A) Calcium salts of higher fatty acids
B) Magnesium salts of higher fatty acids
C) Potassium salts of higher fatty acids
D) Sodium salts of higher fatty acids

Answer 1

The type of soap depends on the alkali added during the saponification process.
In hard soap, glycerin content is removed due to the addition of a salt which causes the soap hard.

Complete Solution :
- Ordinary water cannot remove the dirt from the surfaces, so we use an external agent which can remove the dirt. Soap is the best agent to remove oil and dirt from the surface.
- We generally define soap as the sodium salt of fatty acids but other alkalis are also used with the higher fatty acids to form various types of soaps like liquid soap, hard soap, soft soaps etc.
The difference in addition of the alkali during the saponification process alters the physical and chemical property of the soap.
- Hard soaps are generally made of NaOH lye. During the preparation of soap, common salt is added during the process of saponification. NaCl performs two functions: it precipitates out the soap from the liquid soap solution by the combining effect of the sodium ions with the higher fatty acids and removes the glycerin. Glycerin is the compound that gives a moistening effect for the soap. As the glycerin is removed and the liquid mass of soap turns to a solid hard soap.
One of the examples of hard soap made of sodium salts of fatty acid is sodium stearate.
So, the correct answer is “Option D”.

Additional Information:
- Hard soaps have a greater cleansing effect on ordinary as well as hard water which contains ions like calcium and magnesium.
- Hard soaps are only used as detergents, it can’t be used in the body surfaces as it may deplete the skin and remove the moisture content in the skin.

Note: We usually refer to soap as sodium salts of higher fatty acids but it is not true in every classifications of soap, if in the question it was given as soft soaps then the answer must have been potassium salts of higher fatty acids. OH is used as the lye for the preparation of soft soap. So we must understand the different classifications of soap and the lye used in them.