Soap is actually a sodium or potassium salt made by combining an organic acid with an alkali. Soap is prepared from oils or fats. Oils like olive oil, castor oil, palm oil or any animal fat can be used in the manufacture of soap.
When oils or fats are heated with a solution of sodium hydroxide, they split up to form sodium salt of the respective fatty acid.
Oil or fat + sodium hydroxide -> soap + glycerol
This process is called saponification.
ADVERTISEMENTS:
After saponification, some common salt is added to the solution. This decreases the solubility of soap. It separates from the solution and floats on the surface. It is then removed, purified, dried and made into cakes. Desired colouring agents and perfumes are added after purification, to get different varieties of soaps. Glycerol is recovered from the solution left behind after removing the soap. It is used in making drugs, cosmetics, explosives, paints, etc.
Cleansing action of soap. A typical soap molecule has a rather long structure. It has a head (sodium end) that is attracted to water and dissolves in it. The tail part (hydrocarbon) is oil soluble and tends to dirt particles. After the oil-soluble end weakens the greasy dirt particles, they are easily washed away by water.
Synthetic detergents
Synthetic (soapless) detergents have already replaced soap for laundry purposes. They are derived from petroleum and other sources. Shampoos and washing powders contain detergents. Detergents can work equally well in hard water.
Synthetic detergents are made by reacting concentrated sulphuric acid with the hydrocarbons extracted from crude oils.