Question

While studying the saponification reaction for the preparation of soaps, the teacher suggested to a student to add a small quantity of common salt to the reaction mixture. The function of common salt in this reaction is to:

A. reduce the alkalinity of the soap
B. reduce the acidity of the soap
C. enhance the cleansing capacity of soap
D. favour precipitation of soap

Answer 1

Hint: Saponification is basically the reaction in which the hydrolysis of an ester is carried out with KOH or NaOH to give corresponding alcohol and potassium or sodium salt of the acid. The formula of soap is ${{C}_{17}}{{H}_{35}}COONa$.

Complete step by step solution:
- As we know that the process of making soaps is called saponification.
- There are triglycerides present which are basically animal fats and vegetable oils. When these are reacted with NaOH that is sodium hydroxide, we can see a hard form of soap is formed.
- We can write the equation as: Base+ Ester= Alcohol + Soap
- We know that soap is precipitated as a solid from the suspension by the addition of common salt to the suspension. It is also found that salt decreases the solubility of soap. We can call this process salting out of soap.

Hence, we can say that the correct option is (D), that is the function of common salt in this reaction is to favour precipitation of soap.

Note: - We can see that the saponification process is used in wet chemical fire extinguishers and also for creating hard and soft soaps.
- As we know that Soaps and detergents have cleaning action, but both of these have differences in properties like soaps are sodium salts of long-chain carboxylic acids and have a relatively weak cleaning action. Whereas, detergents are sodium salt of long-chain benzene sulphonic acids and have a strong cleaning effect.