What is the difference between the molecules of soaps and detergents, chemically? Explain the cleansing action of soaps.

Question

Philoid · Accepted Answer

The difference between the molecules of soaps and detergents is tabulated as below-

Soap	Detergent
1.They are sodium or potassium salts of fatty acids.	1.They are sodium or potassium salts of sulphonic acids.
2. They have COO^-Na⁺ group	2. They have –SO₃ Na group
3.They do not work well with hard water, acidic water and saline water.	3.They work well with hard water, acidic water and saline water.
4. They are fully biodegradable.	4. Some detergents having branched hydrocarbon chain are non biodegradable.
5. Example- Sodium stearate, Sodium palmitate.	5. Example- Sodium lauryl sulphate.

Cleansing action of soaps –

1. When soap is dissolved in water, it forms a colloidal suspension in water in which soap molecules cluster together to form spherical micelles.

2. In these micelles the soap molecules are arranged radially with hydrocarbon ends directed towards the centre and ionic ends directed outwards.

3. When the dirty cloth is put in water containing dissolved soap, than the hydrocarbon ends of soap molecules attach to the oil particles of the cloth. The ionic ends remain attached to the water.

4. When the dirty cloth is agitated in soap solution, the oil and grease particles present on the surface and entrapped by soap micelles get dispersed away due to which soap becomes dirty and cloth gets cleaned.

Note- The whole purpose of using soap for washing is to make the oily and greasy dirty particles soluble in water.