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Cleansing Action of Soap

Washing action of soap is due to the emulsification of grease and taking it away in the water alongwith dirt or dust present on grease.

Explanation: the cleansing action of soap can be explained keeping in mind that a soap molecule contains a non-polar hydrophobic group and a polar hydrophilic group. The dirt is held on the surface of clothes by the oil or grease which is present there. Since oil or grease is not soluble in water, therefore, the dirt particles cannot be removed by simply washing the cloth with water. When soap is applied, the non-polar alkyl group dissolves in oil droplets while the polar –COO-Na+ groups remain dissolved in water.

In this way, each oil droplet is surrounded by negative charge. These negatively charged oil droplets cannot coalesce and a stable emulsion is forced. These oil droplets (containing dirt particles) can be washed away with water along with dirt particles.

Advantages of synthetic detergents over soaps

Synthetic detergents are widely used these days as cleansing agents. Synthetic detergents have the following advantages over soaps:

1. Synthetic detergents can be used even in hard water whereas some of the soap gets washed if water is hard.

2. Synthetic detergents can be used even in acidic medium as they are the salts of strong acids and are not decomposed in acidic medium.

3. Synthetic detergents have a stronger cleansing action than soaps.

4. Synthetic detergents are more soluble in water than soaps.

5. Synthetic detergents are prepared from the hydrocarbons obtained from petroleum. This saves vegetable oils which are otherwise used in preparation of soap.

Disadvantages of synthetic detergents

Some of the early synthetic detergents were non-biodegradable that is they were not broken down by bacteria. Thus, they caused water and soil pollution. Effluents containing such detergents reach the rivers, ponds, etc. These detergents persist in water even after sewage treatment and cause foaming in rivers, ponds etc.

This problem has been overcome. It has been found that if straight chain hydrocarbon is used in the detergent instead of a branched chain hydrocarbon then the detergent is biodegradable. All the soaps, on the other hand, are biodegradable.

Another problem is with the use of certain phosphate additives which are added to the detergent. These phosphate additives act as nutrients for algae which form a thick green acum over the river water and upset the animal life in the river. But action has now been taken for this problem also.