Adsorption Chemistry Study Materials
Adsorption:
Unbalanced or residual forces act along the surface of a liquid giving rise to surface tension. Such forces also exist on the surface of a solid. As a result of these residual forces, the surface of a solid has a tendency to attract and retain molecules of other Species with which it is brought into contact. As these molecules remain only at the surface and do not go deeper into the bulk, their concentration is more at the surface than in the bulk of the solid.
“The phenomenon of higher concentration of any molecular species at the surface than in the bulk of a solid is known as adsorption.
The forces involved are intermolecular forces (Van der Walls forces).
Solids when finely divided, have a large surface area and therefore, show this property to a large extent.
The solid that takes up a gas or vapour or a solute from a solution, is called the adsorbent while the gas or vapour or the solute, which is held to the surface of the solid, is; -called the adsorbate.
Adsorption is to be carefully distinguished from absorption. The latter term implies that a substance is uniformly distributed throughout “the body of a solid or a liquid.
Chemisorption:
Adsorption is not necessarily a physical phenomenon always. It may as well be a chemical process involving chemical interaction-between the surface atoms of the adsorbent and the atoms of the adsorbate. This type of adsorption is known as chemisorption.
Applications of Adsorption:
- A very good method of creating a high vacuum is to connect a bulb of charcoal cooled in liquid air to a vessel which has already been exhausted as far as possible by a vacuum pump. Since the magnitude of adsorption at such low temperatures is quite high, the remaining traces of air, in Spit of the low pressure, are adsorbed by the charcoal almost completely.
- Activated charcoal is used in gas masks in which all tonic gases and vapours are adsorbed by the .charcoal while pure air passes through its pores practically unchanged.
- Silica and alumina gels are used as adsorbents for removing, moisture for controlling humidities of rooms.