Classification of Adsorption

Classification of adsorption

Adsorption can be classified into two categories as described below,

(1) Depending upon the concentration: In adsorption the concentration of one substance is different at the surface of the other substance as compared to adjoining bulk or interior phase.

(i) Positive adsorption: If the concentration of adsorbate is more on the surface as compared to its concentration in the bulk phase then it is called positive adsorption.

Example: When a concentrated solution of KCl is shaken with blood charcoal, it shows positive adsorption.

(ii) Negative adsorption: If the concentration of the adsorbate is less than its concentration in the bulk then it is called negative adsorption.

Example: When a dilute solution of KCl is shaken with blood charcoal, it shows negative adsorption.

(2) Depending upon the nature of force existing between adsorbate molecule and adsorbent

(i) Physical adsorption: If the forces of attraction existing between adsorbate and adsorbent are Vander Waal’s forces, the adsorption is called physical adsorption. This type of adsorption is also known as physisorption or Vander Waal’s adsorption. It can be easily reversed by heating or decreasing the pressure.

(ii) Chemical adsorption: If the forces of attraction existing between adsorbate particles and adsorbent are almost of the same strength as chemical bonds, the adsorption is called chemical adsorption. This type of adsorption is also called as chemisorption or Langmuir adsorption. This type of adsorption cannot be easily reversed.

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