Ordinary water does not remove dirt from things because grease and water do not mix. So soap is one of the most common cleansing agent used all over the world. People use soaps and detergents to clean their skin, clothes, utensils and many other objects. Soap is basically a fatty acid salt which can be obtained by boiling fats or oils together with an alkali. When oil is allowed to react with caustic soda solution, the chemical reaction produces soap and glycerin. Both are separated. When soap is applied on a cloth, its molecules break into fatty acid ions and sodium ions. Fatty acid ions are repelled by water but are attracted towards greasy dirt particles. They surround each grease molecule and remove it from the surface of the cloth. These are carried away by the water and consequently the cloth gets cleaned. Other actions, such as agitating, squeezing or rubbing and rinsing help loosen dirt and grease so that water may carry them away.
Detergents clean better than soaps in hard water, (the ‘hardness’ of the water is caused by the presence of calcium and magnesium salts. Soap does not make much lather in hard water but they do not, by themselves, make suds. Suds are not necessary for cleaning but substances that make suds are added to detergents. Many substances are added to a crude soap to make it suitable for use as a toilet soap. Coconut oil is added to make it lather quickly. Dyes, perfumes, water softeners and germicides, which are tiny substances that kill germs are also added.