CBSE Class 10 Answered

isn't there any video based on cleansing action of soaps. if it is not there please explain what are miscelles and cleansing action of soaps in a understandable way using simple words. please answer it as soon as possible

Asked by | 11 Feb, 2012, 10:45: PM

Expert Answer

Soaps are mixtures of sodium or potassium salts of fatty acids which can be derived from oils or fats by reacting them with an alkali (such as sodium or potassium hydroxide) at 80°100 °C in a process known as saponification.

fat + NaOH ---> glycerol + sodium salt of fatty acid

CH₂-OOC-R - CH-OOC-R - CH₂-OOC-R (fat) + 3 NaOH ( or KOH) ------>

CH₂-OH -CH-OH - CH₂-OH (glycerol) + 3 R-CO₂-Na (soap) R=(CH₂)₁₄CH₃

How does Soap Work?

Nearly all compounds fall into one of two categories: hydrophilic ('water-loving') and hydrophobic ('water-hating'). Waterand anything that will mix with water are hydrophilic. Oil and anything that will mix with oil are hydrophobic. When water and oil are mixed they separate. Hydrophilic and hydrophobic compounds just don't mix.

The cleansing action of soap is determined by its polar and non-polar structures in conjunction with an application of solubility principles. The long hydrocarbon chain is non-polar and hydrophobic (repelled by water). The "salt" end of the soap molecule is ionic and hydrophilic (water soluble).

When grease or oil (non-polar hydrocarbons) are mixed with a soap- water solution, the soap molecules work as abridge between polar water molecules and non-polar oil molecules. Since soap molecules have both properties of non-polar and polar molecules the soap can act as an emulsifier. An emulsifier is capable of dispersing one liquid into another immiscible liquid. This means that while oil (which attracts dirt) doesn't naturally mix with water, soap can suspend oil/dirt in such a way that it can be removed. The soap will form micelles (see below) and trap the fats within the micelle. Since the micelle is soluble in water, it can easily be washed away.

A micelle is formed when a variety of molecules including soaps and detergents are added to water. The molecule may be a fatty acid, a salt of a fatty acid (soap), phospholipids, or other similar molecules.

The molecule must have a strongly polar "head" and a non-polar hydrocarbon chain "tail". When this type of molecule is added to water, the non-polar tails of the molecules clump into the center of a ball like structure, called a micelle, because they are hydrophobic or "water hating". The polar head of the molecule presents itself for interaction with the water molecules on the outside of the micelle.