Soap and detergent - Warriors Against Germs

Awareness regarding soaps and detergents play an important role in achieving effective cleanliness. Detergents can be best defined as a product which is made up of one or more surfactants that result in effective washing. Soaps are made up of potassium or sodium salts of fatty acids which are water soluble in nature.

Cleansing action of soaps and detergents mainly depend upon the surfactants (surface active agents). Surfactants are cleansing agents that are responsible for reducing the surface tension of water so that water can wet the surface. Important functions of cleansing agents in cleaning are emulsification (i.e. dispersion in liquids), catering alkalinity and loosening the liquid. Soaps and detergents are prime examples of surfactants.

Oils and fats, along with strong alkali act as key ingredients of soap making industries. Oils and fats which are helpful in soap making industries are usually plant or animal originated. These ingredients of soap used are usually made up of a combination of various types of triglycerides. Soaps are produced by treating oils and fats chemically with strong alkalis. Alkalis used in soap production are usually water soluble salts of alkali metals like potassium or sodium. The most commonly used alkalis in soap production are hydroxide salts of potassium or sodium. Saponification is a method which is most widely used in soap industries to produce soaps. In this method the oils or fats are heated and then treated with a strong alkali. The product produced is soap, water and glycerine. In general soap making, the process involves a neutralization reaction in which an acid reacts with an alkali.

Detergent is a cleansing agent which in manufactured in huge chemical plants. A detergent is made up of surface active molecules which posses surface active properties. Detergent molecules are commonly long chain or cluster of atoms. The key ingredient used in the manufacturing of detergents is hydrocarbons which are usually derived from fats, oil or petroleum. Depending upon the surfactant required (i.e. anionic or non-ionic), different procedure for manufacturing is followed. For an anionic surfactant, chemicals which are water loving (sulphur dioxide, sulphuric acid) reacts with the hydrocarbons to produce a new acid. An alkali is added to the new acid which results in the formation of anionic surfactant. Non-ionic surfactants are formed by converting the hydrocarbon into an alcohol. This alcohol is then reacted with fatty alcohol along with ethylene oxide.

Working of soaps and detergents

Three different types of energies are used in order to obtain good cleaning results. They are:

  • Chemical energy
  • Thermal energy
  • Mechanical energy

Soap or detergent provides the necessary chemical energy required. Water provides the thermal energy needed and hand or machine provides the mechanical energy. To explain the working let us assume there is an oily stain on a piece of cloth. When dipped in water, it alone cannot remove the stain. When soap or a detergent is added, water hating end of the surfactant gets opposed by water but it is grabbed by the oil stain and at the same time water loving part is attracted by the water molecules. These forces which are opposing to each other loosen the oil stain on application of mechanical force and attach it to the water thus leaving your cloth stain-free.

Practise This Question

Assertion (A): Hard water forms sticky precipitate with soap.
Reason (R): Hard water contains calcium and magnesium ions