Explain the mechanism of the cleansing action of soaps

Explanation

Dust sticks to our clothes or body due to oil secreted by oil glands present on our skin. Cleansing action of soap involves the removal of this oil in the form of an emulsion of oil in water. Without oil, dirt cannot stick to out clothes or body and hence is removed.

As we know, soaps are generally sodium salts of higher fatty acids. Let us take the example of sodium sterate. When dissolved in water it ionises to give sodium ions, Na and sterate ions, `CH_3- [CH_2]_(16)-COO`. The long hydrocarbon chain of the sterate ion is hydrophobic or water hating. As such, this hydrophobic end or tail dissolves in the grease deposit and convert it into tiny droplete, to form micelle. These grease micelles become negatively charged due to the charge given to them by the negatively charged sterate ions. Repulsion of like charges covering each grease micelle prevent them to come together.
These micelles are then removed by the water used for rinsing. Thus the main function of the soap is to reduce oil or grease to colloidal particles.