Soaps are sodium or potassium salts of long chain carboxylic acids. They are using as cleansing agents to remove dirt, oil from the skin and clothes.
Generally soaps are prepared by heating animal fat or oil with alkalies like sodium hydroxide or potassium hydroxide. This is saponification reaction.
Fat or Oil + Alkali → Soap + Glycerol
Glycerol is by -product formed in the saponification reaction. This is used in the preparation of cosmetics, paints and even explosives.
The Soap molecule has two ends with different properties. They are hydrophillic end and hydrophobic end.
Hydrophillic end :
Hydrophillic end dissolves in water.
Hydrophobic which dissolves in hydrocarbons.
Cleaning action of soap:
The cleaning action of soap is due to micelle formation and emulsion formation. Inside water a unique orientation forms clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends on the surface of cluster. This results in the formation of micelle.
Soap in the form of micelle cleans the dirt as the dirt will be collected at the centre of micelle.
This property of soap makes it an emulsifier. The dirt suspended in micelles is easily rinsed away. This is known as cleaning action of soap.
In hard water soap don't give lather .Hard water contains calcium and magnesium salts, which combine with soap molecules to form insoluble precipitates known as scum.
Detergents have almost the same properties as soaps but they are more effective in hard water. Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in water.