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SURFACE CHEMISTRY ®; ©:

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Surface chemistry deals with phenomena that occur at the surfaces or interfaces., , interface between a solid and a gas may be represented by solid-gas or solid/gas., , Due to complete miscibility, there is no interface between the gases, , corrosion, electrode processes, heterogeneous catalysis, dissolution and, crystallisation occur at interfaces., , To accomplish surface studies meticulously, it becomes imperative to have a, really clean surface. Under very high vacuum of the order of 10-8 to 10-9, pascal, it is now possible to obtain ultra clean surface of the metals.

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The accumulation of molecular species at the surface rather than in the bulk of, a solid or liquid is termed adsorption., , The molecular species or substance, which concentrates or accumulates at the, surface is termed adsorbate., , material on the surface of which the adsorption takes place is called adsorbent.

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Adsorption in action, , (i) If a gas like O,, H,, CO, Cl,, NH, or SO, 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, say methylene blue, when animal, charcoal is added and the solution is well shaken, it is observed, that the filtrate turns colourless. The molecules of the dye, thus,, , accumulate on the surface of charcoal, i.e., are adsorbed., , (iii) Aqueous solution of raw sugar, when passed over beds of animal, charcoal, becomes colourless as the colouring substances are, , adsorbed by the charcoal., , (iv) The air becomes. dry in the presence of silica gel because the water, molecules get adsorbed.on the surface of the gel., , It is clear from the above examples that solid surfaces can hold, the gas or liquid molecules by virtue of adsorption. The process of, removing an adsorbed substance from a surface on which it is, , adsorbed is called desorption.