XII Chemistry BIEK Topic - Detergent (Short Note)

Detergent (Short Note)
Definition
Detergents are the salts of alkyl sulphate or aryl sulphate that improves the cleaning action of solvents, particularly ionic solvents.




Explaination
Detergents are long chain molecules, which when dissolve in water dissociate into positive and negative ions, these ions react with the ions of dirt and grease to produce soluble compounds with are readily carried away by the water molecules.




General Formula
Detergents are sodium or potassium salts of alkyl sulphate or aryl sulphate.

R-OSO3-Na+ Sodium Alkyl Sulphate

Where R is an alkyl group containing 7 to 18 carbon atoms. Soaps are sodium or potassium salts of long chain fatty acids.

R - COO-Na+




Composition of Detergents
Detergents are composed of two main parts namely.

1. Hydrophobic Part

2. Hydrophilic Part


1. Hydrophobic Part

It is a water repelling part of detergent, which consist of long hydrocarbon chain. The hydrocarbon chain being non-polar attracts dirt particles, which are normally non polar, i.e. greasy or oily molecules. Therefore, this part of detergent removes dirt particles from thing being washed and water takes away the dirt particles with it.


2. Hydrophilic Part

Hydrophilic part of the detergent is water attracting part. It consists of small ionic groups such as sulphonate (SO3) and sulphate (-SO3-). The hydrophilic group being ionic gets attracted by the polar water molecules and in this way, this part of the detergent removes the ionic dirt particles.




Advantage of Detergents
Detergents can act in hard water, since the calsium and magnesium salts of detergents are soluble in water. Whereas, the corresponding salts of soap are insoluble in water. Thus detergents are better cleaning agents than soaps.

Disadvantages of Detergents
One disadvantage of detergent over soap is that hydrocarbon chain, unlike those of soaps, which are derived from food substances (fats and oil) cannot be broken down by bacteria and dispersads. Therefore, it causes water pollution.