Cleansing Action of Soaps and Detergents

Sodium and Potassium salts of fatty acids are called soaps. Potassium soaps are soft and hence used as a toilet soap. Sodium soaps are hard soaps and hence used in washings.

Cleansing Action of Soaps and Detergents

The cleansing action of soap is due to
(1) Solubilisation of grease into the micelle
(2) Emulsification of grease


In relatively strong solution the soap (or detergent) anions spontaneously form a micelle. The hydrocarbon tails are in the interior of the micelle and COO– ions on the surface. The grease stain is thus absorbed into the interior of the micelle which behaves like liquid hydrocarbons. As the stain is detached from the fabric, the dirt particles sticking to the stain are also removed.


The soap or detergent molecules are ionised in water. The anions are made of oil-soluble hydrocarbon tails and water-soluble polar heads. Thus soap anion has a long hydrocarbon tail with a polar head, —COO–. When soap solution is added to a fabric, the tails of the soap anions are pegged into the grease stain. The polar heads protrude from the grease surface and form a charged layer around it. Thus by mutual repulsions the grease droplets are suspended in water. The emulsified grease stains are washed away with soap solution.

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Author: Asha Kurian07 Jul 2010 Member Level: Gold   Points : 2

The cleansing action of a soap is related to the physical & chemical properties.Several factors are responsible for this cleansing action. They are
1. Adsorption
2. Surface tension
3. Emulsifying power
4. Wetting action
5. Electrostatic force of the polar soap molecule.

When the soap particles are dissolved in water,it lowers the surface tension of water.When a greasy particle is dipped in it,the lowering of surface tension enables the water to wet & come in close contact with this greasy surface.The decrease in surface tension is the main property which enables the soap to wet the surface of a fabric.
Another property is the Emulsifying power.Soap forms a protective coating on the fabric surface.As a result the oil particles are not able to come together again.By vigorously shaking with water,this dirt particles are removed.

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