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  • It is a salt of long-chain fatty acids.
  • It consists of a long hydrocarbon chain with a carboxylic acid group on one end (ionic end) bonded to a metal ion.
  • The hydrocarbon end is non-polar and is soluble in non-polar substances.
  • The ionic end is polar and is soluble in polar substances, say water.


Preparation of Soap Oils and fats are the esters of glycerol and higher fatty acids. Na or K salt of these higher fatty acids are called soaps.
Properties of Soaps
  • When soaps are used in hard water that contains ions such as Ca2+, Mg2+ and Fe2+, they form an insoluble scum.
  • Soaps undergo hydrolysis in water and the solutions tend to be alkaline in nature.
  • With mineral acid, soaps are converted into fatty acids.
Cleansing Action of Soaps


Soaps are prepared by the alkaline hydrolysis of fats and oils (the process known as saponification). The by-product of this reaction is glycerol.


  • Hydrocarbon end (non-ionic, hydrophobic) attaches to the dirt or grease to form structures called micelles.
  • Ionic end (hydrophilic) attaches itself to water molecules.
  • These micelles are arranged radially.
  • The hydrophilic end attached to water pulls out the dirt from the fabric.
  • These micelles can be washed away with water.


  • It is derived from a Latin word meaning ‘surface active’.
  • It is also called soapless soap since it does not form insoluble scum with magnesium and calcium ions present in hard water.
  • It is a sodium salt of long-chain benzene sulphonic acid or long-chain alkyl hydrogen sulphate.
Preparation of Detergent It is prepared by the reaction of dodecyl alcohol with sulphuric acid. Dodecyl sulphate is converted into sodium salt by a reaction with sodium hydroxide.
Sodium Lauryl Sulphate (sodium dodecyl sulphate, SDS)

Description: FIG-7a.tif

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