Chemistry Revision Notes of Some Important Chemical Compounds For NDA Part-1
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Cleansing Agents

In fact, those chemicals which concentrate at the surface of the solution or interfaces, reduce tension of the solution and help in removing dirt and dust by emulsifying grease are are known as surfactants. Soaps and detergents belong to this class.

`text(Soaps) :` Soaps are water-soluble sodium or potassium salts of higher fatty acids like stearic acid, oleic acid, palmitic acid etc. Soap are obtained by the alkaline hydrolysis of oils and fats. Only glycerides of fatty acid give soaps on alkaline hydrolysis.

`text(Raw Materials) :` The important raw material used for the manufacture of soaps are :

(i) Oil or Fat Mustard oil, mohwa oil, coconut oil, cotton seed oil, olive oil or animal fat.

(ii) Fillers : The substance added to increase the weight and volume of soaps e.g. sodium silicates , powdered pumice , starch , sodium carbonate.

(iii) Alkali Caustic soda for hard or washing soaps and caustic potash for soft soap is used for saponification .

(iv) Colouring Material

ZnO White colour
Methylene blue Blue colour
Uranium Yellow
Eosine Red

(v) Perfumes : Perfumes are used to make soap pleasant smelling e.g. lemon grass oil.

Types of Soaps

There are following types of soaps :

(i) Washing Soaps : These are made from cheaper fats like mohwa oil, resin oil etc.

(ii) Toilet Soaps : These are made from best quality animal or vegetable fats or mixture of both. These soaps do not injure the skin.

(iii) Shaving Soaps : These toilet soaps contain gum and glycerol. Their mildness increases by adding potassium carbonate. Resin is also added to shaving soaps as it forms lather well.

(iv) Liquid Soaps : These soaps are obtained by the action of coconut oil and caustic potash and contain about 8% of water.

(v) Medicated Soaps : Toilet soaps containing some substance of medicinal value, e.g. carbolic soap, neem soap etc.

(vi) Metallic Soaps : These soaps contains salt of metals other than sodium and potassium.

(vii) Transparent Soaps : These are prepared by dissolving toilet soaps in alcohol and evaporating the filtrate. These contain glycerol.

(viii) Floating Soaps : These soaps are obtained by beating large amount of air into soap while it is in creamy stage.

Detergents

Detergents are generally ammonium or sulphonate salts of long chain carbroxylic acids. Although these do not contain soaps like sodium salts of fatty acids. Hence, these are known as 'soapless soap'.

`=>` These can he used even in acidic solutions and have a strongest cleansing action.

`=>` These are mote soluble in water and can be used with hard water as these produces no precipitates with `Ca^(2+) , Mg^(2+) , Fe^(3+)` ions present in hard water. They are used in powder form for domestic purpose.

`=>` The liquid form may be used for dish washing, cleaning of floors etc.

`=>` Biological degradation is an important property of good detergent.

`text(Cleansing Action of Soap or Detergent)` : Water alone will not remove grease or oil from clothes because oil and grease present in soil repel the water molecules. Both soaps and detergents share a critical chemical property - they are surface-active agents, or surfactants. In other words, they reduce the surface tension of water. Because of reduction of surface tension, water soaks more easily in clothes and removes stains faster.
The carboxylate end of the soap molecule is attracted to water. It is called the hydrophilic (water-loving) end. The hydrocarbon chain is attracted to oil and grease and repelled by water. It is known as the hydrophobic (water-hating) end. The water-hating end is repelled by water but attracted to the oil in the soil. At the same time, the water loving end is attracted to the water molecules. These opposing forces loosen the soil and suspend it in the water. Warm or hot water helps dissolve grease and oil in soil. Washing machine agitation or hand mobbing helps pull the soil free.

Note : The cluster of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster is called a micelle.


 
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