Soaps clean surfaces on the principle-based on

Soaps and detergents clean surfaces primarily by lowering the surface tension of water [1]. Water molecules have high surface tension, which prevents them from spreading and wetting surfaces effectively. Soap molecules, which are sodium or potassium salts of long-chain carboxylic acids, act as surfactants [1]. These molecules possess a dual nature: a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail. When added to water, they reduce the surface tension, allowing the water to spread and penetrate fabrics or surfaces. The hydrophobic tails attach to oily dirt, while the hydrophilic heads remain in the water, forming structures called micelles [1][3]. This process emulsifies the oil and grease, suspending them in the water so they can be easily rinsed away [1][4]. Thus, the reduction of surface tension is the fundamental principle enabling the cleaning action [1].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Activity 4.10 > p. 75
2. [3] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > QUESTIONS 1. Would you be able to check if water is hard by using a detergent? 2. People use a variety of methods to wash clothes. Usually after adding the soap, they 'beat' the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes? > p. 76
3. [4] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > CH COOH CH CH OH CH C C CH CH H O 3 3 2 3 2 3 2 Acid O (E - + - - - - - + thanoic acid) (Ethanol) (Ester) O > p. 73