Question

While preparing soap, a small quantity of common salt is generally added to the reaction mixture of vegetable oil and sodium hydroxide. Which one of the following may be the purpose of adding common salt?

• A. To reduce the basic nature of the soap
• B. To make the soap neutral
• C. To enhance the cleansing power of the soap
• D. To favour the precipitation of the soap

Answer 1

The correct option is D To favour the precipitation of the soap

The saponification reaction is exothermic in nature, because heat is liberated during the process. The soap formed remains in suspension form in the mixture. Soap is precipitated as a solid from the suspension by adding common salt to the suspension. Hence, salt helps in precipitation. This process is called salting out of soap.