Chemqueries: May 2019

Friday, 10 May 2019

Adsorption

What is Adsorption?
  • The phenomenon of adsorption was introduced by Scheele during the discovery of uptake of gases by charcoal.
  • The term adsorption was given by Kayser and this concept of adsorption was developed by Kayser and Raymonds.
  • When a solid surface is exposed to a gas or a liquid, molecules from the gas or liquid accumulates at the surface. The phenomenon of concentration of a gas or a liquid at a solid surface rather than in its bulk is called Adsorption.
  • Adsorption is caused by a type of Vanderwall's force which exists between the molecule known as London Dispersion Force
  • The substance that concentrates at the surface is called adsorbate and the solid at the surface of which the concentration occurs is called adsorbent.
Example of Adsorption:
  • Finely divided charcoal if stirred into a dilute solution of methylene blue, the dye molecule are adsorbed by the charcoal particles and the depth of color of the solution decreases appreciably.
  • If gas like SO2 , Cl2 , NH3S is treated with powdered charcoal in a closed vessel, the gas molecule adsorbed on the charcoal surface and the gas pressure is reduced.
  • The common adsorbents are charcoal(vegetable and animal),  silica gel(prepared by heating a mixture of sodium silicate and 10% HCl at 50-degree centigrade), a metal such as Ni, Cu, Ag, Au, Pt, and colloids.