Adsorption Introduction There are several examples, which reveal that the surface of a solid has the tendency to attract and retain the molecules of the phase with which it comes into contact. Thesemolecules remain only at the surface and do not go deeper into the bulk. Adsorption The accumulation of molecular species at the surface rather than in the bulk of a solid or liquid is termed adsorption. Adsorbate The molecular species or substance, which concentrates or accumulates at the surface is termed adsorbate . Adsorbent The material on the surface of which the adsorption takes place is called adsorbent . Adsorption in action (i) If a gas like O2 , H2 , CO, Cl2 , NH3 or SO2 is taken in a closed vessel containing powdered charcoal, it is observed that the pressure of the gas in the enclosed vessel decreases. The gas molecules concentrate at the surface of the charcoal, i.e., gases are adsorbed at the surface. (ii) In a solution of an organic dye,