Question

Explain the mechanism of the cleaning action of soap.

Answer 1

i. A soap molecule consists of two dissimilar ends. One end hydrophilic(Attracts towards water) and other end is hydrophobic (Moves away from water).

ii. The hydrophobic end which is water repellant is consistent of hydrocarbon chain, whereas, the hydrophilic end which is water soluble is polar due to presence of carboxylate anion. Thus, a soap molecule is represented as:

    a.  When a soap is dissolved in water, many molecules come together and form a group called micelle because, their hydrocarbon chains come together and the polar ends are projected outwards.

b.When a cloth with spot of stains in soaked in soap solution, soap dissolves the tiny droplet of stain towards the centre of micelle. This forms oil in water type emulsion . The anions at outer end of micelle repel each other and hence, they do not precipitate . When the cloth is rubbed, bigger molecules of stains  break into small emulsified molecules. Thus, the removal of stains takes place in the mechanism.

Note: Soaps are potassium and sodium alkaline salts of carbonates.

Answer 2

        Soap molecules form micelles, which are sodium or potassium salts of fatty carboxylic acids of the form $(RCOO ^- Na^+)$ or $(RCOO^-K^+)$

O/\/\/\/\/\/\/\/\/\/\/ - a micelle (each end has a methyl group [$CH_3$])
Eg: sodium sterate ($C_{17}H_{35}COONa$),etc

     One end of the micelle is hydrophilic (Meaning : water loving) and the other  end is hydrophobic(Meaning: water hating).

     Hydrophilic end will reacts(or mix) with water and the hydrophobic end will react (or mix) with the dirt(which are mostly oil or grease).

      So, when we pour water, when water runs away the hydrophilic end goes with it, and as the micelle is a chain it drags hydrophobic end with it and the hydro phobic end pulls the dirt with end and hence,the dirt is removed.
=> This effect of soap is known as cleanzing action of soap.