Soaps are the metallic salts of higher fatty acids such as palmitic, stearic, oleic, etc. the sodium and potassium salts are the common soaps which are soluble in water and used for cleansing purposes. Soap of other metals such as calcium, magnesium, zinc, chromium, lead, etc., are insoluble in water. These are not used for cleansing purposes but for other purposes (lubricants, driers, adhesives, etc.)
Ordinary soaps (sodium and potassium) are the products of hydrolysis of oils and fats with sodium hydroxide or potassium hydroxide. The oils and fats are mixed glycerides and thus soaps are mixtures of salts of saturated and unsaturated long chain carboxylic acids containing 12 to 18 carbon atoms. This process always yields glycerol as a byproduct.
Type of soaps
Hard Soap:-these are obtained from cheap oils and fats using sodium hydroxide. These contain free alkali and are used for washing purposes.
Soft Soaps:- These are obtained from good oils using potassium hydroxide. These do not contain free alkali and are used as toilet soaps, shaving creams, in shaving sticks (pot, sod, stearate) and shampoo.
Transparent Soap: - these are formed by dissolving toilet soaps in alcohol and evaporating the filtrate. They contain glycerol.
Medicated Soap: - Toilet soaps containing some medicinal important substances are called medicated soaps.
Metallic soaps: - these are soaps of metals other than sodium and potassium.