Question

Why is it advised to add common salt while preparing the soap?

Answer 1

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. This process is called Salting out of Soap.

Answer 2

Common salt is added to precipitate out all the soap from the aqueous solution. Adding of common salt to soap solution decreases the solubility of soap due to which all the soap precipitates out from the solution in the solid form. This process is called salting out of soap.