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Cleansing Agents

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Cleansing Agents - Lesson Summary

The word "detergent" is a general term used to denote a cleansing agent.

Two types of detergents: Soaps and Synthetic detergents are used as cleansing agents. These agents improve the cleansing properties of water. They help remove the oily and fatty substances that bind dirt and other material to the skin (or) the fabric.

Soaps used for cleaning are sodium (or) potassium salts of naturally occurring long-chain fatty acids such as stearic, oleic and palmitic acids.

Soaps that contain sodium salts are formed by heating oil (or) fat of vegetable (or) animal origin with an aqueous sodium hydroxide solution.

The alkaline hydrolysis of oils and fats is known as saponification.

During reaction esters of fatty acids are hydrolysed and the soap obtained remains in colloidal form. The soap and the glycerol are separated by adding concentrated sodium chloride solution to the mixture.

The glycerol dissolves in the salt solution, but the soap is insoluble, floats on the surface of the solution from where it is removed. Glycerol from the solution is recovered by fractional distillation.

Potassium soaps, produced by the saponification of fats with potassium hydroxide, are usually softer and more soluble than sodium soaps.

Soaps may vary in composition and method of processing.

Ex: Substances of medicinal value are added to medicated soaps. Similarly, glycerol and a gum called rosin are added while preparing shaving soaps. Glycerol prevents rapid drying, while rosin forms sodium rosinate that lathers well. Similarly, laundry soaps contain fillers like sodium rosinate, sodium silicate, borax and sodium carbonate.

Transparent soaps are made by dissolving the soap in ethanol and then evaporating the excess of solvent. Soaps that float on water are made by beating air into them before they harden.

In preparing soap powders and scouring soaps, an abrasive agent such as powdered pumice (or) finely divided sand are added, along with builders such as sodium carbonate and trisodium phosphate. The builders enable the soap to act at a faster rate. In preparing toilet soaps, good quality fats and oils are used and excess alkali is removed. Perfumes and colours are added to make them attractive.

Soaps are good cleaning agents, but they do not work with hard water. As hard water has high mineral content that primarily consists of calcium and magnesium ions.

When these ions come into contact with sodium or potassium soaps, they form insoluble calcium and magnesium soaps, thus rendering them useless as cleansing agents.

Calcium and magnesium soaps form a white precipitate called scum in water and hinder cleaning by sticking to the cloth fibre skin (or) hair, thus preventing the formation of lather.

Synthetic detergents are cleansing agents that have all the properties of soap, but do not contain any soap.

Synthetic detergents are classified into three main categories.

           → Soaps
           → Synthetic detergents
                • Anionic detergents                   
                • Cationic detergents                   
                • Non-ioninc detergents

These are anionic detergents, cationic detergents and non-ionic detergents.

Anionic detergents are sodium salts of sulphonated long chain alcohols (or) hydrocarbons.

Cationic detergents are quaternary ammonium salts of amines with acetates, chlorides and bromides as anions.


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