How soap cleans?






Soaps and detergents are used frequently in our daily life. We use them to wash our hands and clean our clothes without ever really paying attention to how they work. Beneath the plain white surface of a bar of Ivory soap lays an intriguing history and a powerful chemistry!!!!!!!!!!!



There are substances which can be dissolved in water (salt for example), and others that can't (for example oil). Water and oil don't mix together, so if we try to clean an oily stain from a cloth or from the skin, water is not enough. We need soap to help us immediately get rid of the oil.





A soap molecule is a tadpole shaped structure, whose ends have different polarities at one end is the long hydrocarbon chain that is non-polar and hydrophobic, i.e., insoluble in water but oil soluble. At the other end is the short polar carboxylate ion which is hydrophilic i.e., water soluble but insoluble in oil and grease.

Because of this dualism, soap molecules act like a diplomat, improving the relationship between water and oil. How? When soap is added to the water, agitating it tends to concentrate the solution on the surface and causes foaming. This helps the soap molecules make a unimolecular film on the surface of water and to penetrate the fabric. The short polar end (head) containing the carboxylate ion, face the water away from the dirt. The hydrophilic heads of its molecules stay into the water (they like it!). The long non-polar end of a soap molecule that are hydrophobic, gravitate towards and surround the dirt (fat or oil with dust absorbed in it). A number of soap molecules surround or encircle dirt and grease in a clustered structure called 'micelles', which encircles such particles and emulsify them.

An emulsion of oil in water is then formed, this means that the oil particles become suspended and dispersed into the water. Thus, those oil particles are liberated from the cloth or the skin, and the emulsion is taken away with the rinsing.

The subsequent mechanical action of rubbing or tumbling dislodges the dirt and grease from the fabric. These get detached and are washed away with excess of water leaving the fabric clean. Oh what a magic you did not know, yes you just saw your clothes clean this is what happens!