AIM : Investigation of the foaming capacity of different washing soaps and the effect of addition of sodium carbonate on them.

Introduction : soaps are the sodium or the potassium salts of long chain fatty acids such as Stearic acid (C17H 33COOH), Oleic acid (C 17H33COOH), Palmitic acid (C15H 31COOH) and are represented as RCOONA or RCOOK, Where R corresponds to the long chain alkyl group. A soap molecules consists of two parts:

(i)a polar end (-COO Na or –COOK) is hydrophilic in nature, i.e. soluble in water and,

(ii) A non-polar end (long chain alkyl group) which is lipophilic i.e. soluble in oil.

The cleansing action of soap is based on the solubility of the long chain alkyl group in grease or oil droplet (i.e. dirt) and that of polar part, i.e. –COO Na or –COOK in water.

During cleansing of cloth by soap , there is formation of an emulsion between oil and water which is stabilized by soap molecule which acts as emulsifying agent. When dirty cloth is dipped in soap water ,the oil base dirt become soluble in hydrocarbon part while water soluble dirt gets dissolved In polar part (-COO Na or –COOK). Now, the dirt is washed away from the cloth, when it is treated with excess of water.

The foaming capacity of a soap In water is defined as the extent to which it produces foam with water and it corresponds to a measure of its washing capacity.

The foaming capacity of soap depends upon :

1. The nature of the soap (alkyl group) and 2. The quality of water used.

It has been observed that soaps easily produce lather in soft water than in hard water. This is due to presence of calcium and magnesium ions (Ca2+¿ ¿and Mg2+¿¿) in hard water is form Insoluble calcium and magnesium salts of fatty acids that result in formation of scum. 2C17H35COONa + Ca2+¿ ¿ → (C17H35COO¿2Ca + 2Na+¿¿

C17H 35COONa + Mg2+¿¿ → (C17H35COO ¿2Mg + 2Na+¿¿

However on addition of sodium carbonate, the calcium and magnesium Ions are precipitated as their insoluble carbonates and it increases the foaming capacity of the soaps.