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Soaps and Detergents


Soaps are sodium or potassium  salts of long chain  carboxylic acids. They are using as cleansing agents to remove dirt, oil from the skin and clothes.

Generally soaps are prepared by heating animal fat or oil with alkalies like sodium hydroxide or potassium hydroxide. This is saponification reaction.
Fat or Oil + Alkali → Soap + Glycerol

Glycerol is by -product formed in the saponification reaction. This is used in the preparation of cosmetics, paints and even explosives.

The Soap molecule has two ends with different properties. They are hydrophillic end and hydrophobic end.
Hydrophillic end :
Hydrophillic end dissolves in water.

Hydrophobic end:
Hydrophobic which dissolves in hydrocarbons.

Cleaning action of soap:
The cleaning action of soap is due to micelle formation and emulsion formation. Inside water a unique orientation forms clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends on the surface of cluster. This results in the formation of micelle.

Soap in the form of micelle cleans the dirt as the dirt will be collected at the centre of micelle.
This property of soap makes it an emulsifier. The dirt suspended in micelles is easily rinsed away. This is known as cleaning action of soap.

In hard water soap don't give lather .Hard water contains calcium and magnesium salts, which combine with soap molecules to form insoluble precipitates known as scum.

Detergents have almost the same properties as soaps but they are more effective in hard water. Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in water.


  • LearnNext Video

  • YouTube Video

  • YouTube Video

Activities & Simulations

Activity 1
Cengage.com has created an animated video on "Soap Micelle Formation". This video teaches students how the soap molecules remove dirt from the clothes. This video clearly shows the formation of micelle. After watching the video students can also attempt the quiz.
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Activity 2

Amrita.olabs.co has created student useful interactive simulation on Saponification :The Process of Making Soap. This simulation shows how oil or fats reacts with sodium hydroxide solution and get converted into glycerol and soap. This video gives real lab experience to students and also provides inference for each step of the reaction mechanism. 
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Activity 3
Amrita.olabs.co has created student interactive simulation on cleansing capacity of soap with soft and hard water. This simulation help to compare the foaming capacity of soap with different samples of water. This video gives real lab experience and also provides inference at each step.
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