Question

Cleansing action of soap occurs because:

• A. oil and grease can be absorbed into the hydrophobic centres of soap micelles and washed away
• B. oil and grease can be absorbed into hydrophilic centres of soap micelles and washed away
• C. oil and grease can be absorbed into both hydrophilic and hydrophobic centres but cannot be washed away
• D. cleansing action is not related to micelles

Answer 1

The correct option is A oil and grease can be absorbed into the hydrophobic centres of soap micelles and washed away

A micelle is an aggregate of surfactant molecules dispersed in a liquid colloid. When surfactants are present above critical micelle concentration, they can act as emulsifiers that will allow a compound that is normally insoluble (in the solvent being used) to dissolve.

This occurs because the insoluble species can be incorporated into the micelle core, which is itself solubilized in the bulk solvent by virtue of the head groups' favorable interactions with solvent species.

Example of this phenomenon is detergents (a soap micelle has a hydrophilic head that is in contact with the water and a center of hydrophobic tails, which can be used to isolate grime), which clean poorly soluble lipophilic material (such as oils and waxes) that cannot be removed by water alone. Detergents clean also by lowering the surface tension of water, making it easier to remove material from a surface.