Soaps and Detergents


LearnNext Lesson Video

Soapnut powder has been in use for almost 3,000 years. And still in many parts of India, soap nut powder is using as a natural soap to remove oil.

Soap is a sodium salt or potassium salt of long chain fatty acids having cleansing action in water. They are using as cleansing agents to remove dirt, oil from the skin and clothes.
Sodium stearate, sodium oliate and sodium palmitate formed using stearic acid oleic acid and palmitic acid.

Preparation of soap in laboratory:
Animal fat or vegetable oil act as glyceride or glyceryl ester. And sodium hydroxide and potassium hydroxide act as bases.

Take about 30 ml of vegetable oil in a beaker. Then add 60 ml of 20% sodium hydroxide solution to it.
This mixture is heated slowly till it boils. After the mixture has boiled for five to ten minutes add 5grams of sodium chloride in order to separate soap from the solution. Allow the solution to cool. The creamy layer floating on top of the solution is the soap.  
Thus soap is prepared by hydrolysing fat or oil with bases such as sodium hydroxide or potassium hydroxide. This process of soap preparation is known as saponification

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

Commercial preparation of soap: 
It involves mixture of oil or fat and a strong solution of sodium hydroxide is boiled in an iron tank which leads to the formation of a sodium salt of fatty acid or soap and glycerol.
Once the soap is formed, it is separated with the help of sodium chloride. Sodium chloride also reduces the solubility of soap. Since the soap is lighter, it floats like cream on the solution.  
It is separated from the solution, suitable chemicals are added for colour and odour and then it is cast into moulds.
When the soap cools and solidifies, it is cut out into desired shapes and packed.Glycerol, which exists in a dissolved state in the solution, is separated with the help of distillation.
It is possible to prepare different types of soaps from different salts of fatty acids. 

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.

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Activities & Simulations

Activity 1 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 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 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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