Question

Assertion :Small quantity of soap is used to prepare a stable emulsion. Reason: Soap lowers the interfacial tension between oil and water.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

Soaps and detergents act as surfactants (gets water to wet the fibres) and as emulsifiers (separates the dirt from the fibres and suspends it so the water can rinse it away).

Soaps and detergents form micelles which are spherical particles with a hydrophobic interior and hydrophilic exterior that dissolves in the water causing a lather.

Example: $C_{17}{H}_{35}COONa$ (Sodium lauryl sulphate)

In order to prepare stable emulsions, it is important to add a third component known as emulsifier or emulsifying agent in suitable amounts. Several types of emulsifiers are given below:
(i) Long chain compounds with polar groups such as soap, sulphonic acid, sulphates etc.
(ii) Most of the lyophilic colloids also act as emulsifiers such as glue, gelatin etc.
(iii) Certain insoluble powders as clay, lamp, black etc.
(iv) Soluble substances like iodine also act as emulsifiers.