Adsorption - Practice Questions & MCQ

Now as you know about Freundlich isotherm, let us discuss one of the important application of this isotherm in adsorption from solution phase

Solids can adsorb solutes from solutions also. When a solution of acetic acid in water is shaken with charcoal, a part of the acid is adsorbed by the charcoal and the concentration of the acid decreases in the solution.

The precise mechanism of adsorption from solution is not known. Freundlich’s equation approximately describes the behavior of adsorption from solution with a difference that instead of pressure, concentration of the solution is taken into account, i.e.,

(C is the equilibrium concentration, i.e., when adsorption is complete).

Let us discuss about the various applications of adsorption.

1. Production of high vacuum: A high vacuum can be created by keeping charcoal or other adsorbent in a vessel which has already been evacuated by a vacuum pump. The left in gases are adsorbed by charcoal which helps in producing a high vacuum.
2. Gas masks: Gas mask (a device which consists of activated charcoal or mixture of adsorbents) is usually used for breathing in coal mines to adsorb poisonous gases. Poisonous gases like methane, carbon dioxide, etc. can be selectively adsorbed by the gas masks containing activated charcoal. Gas masks are frequently used by the miners.
3. Removal of colouring matter from solutions: Animal charcoal removes colours of solutions by adsorbing coloured impurities.In sugar industries, the crude sugar is decolourised by treating sugar solution with charcoal powder.The coloured impurities are preferentially adsorbed onto charcoal powder.
4. Control of humidity: Silica and aluminium gels are used as adsorbents for removing moisture and controlling humidity. Silica gel is often used to remove moisture and thus controls humidity.
5. Heterogeneous catalysis: Adsorption of reactants on the solid surface of the catalysts increases the rate of reaction. There are many gaseous reactions of industrial importance involving solid catalysts. Manufacture of ammonia using iron as a catalyst, manufacture of H2SO4 by contact process and use of finely divided nickel in the hydrogenation of oils are excellent examples of heterogeneous catalysis
6. Adsorption indicators: Surfaces of certain precipitates such as silver halides have the property of adsorbing some dyes like eosin, fluorescein, etc. and thereby producing a characteristic colour at the end point. Adsorption indicators in volumetric titrations are the examples of adsorption from solution.e.g., starch +iodine.
7. Chromatographic analysis: Chromatographic analysis based on the phenomenon of adsorption finds a number of applications in analytical and industrial fields.Separation and purification of substances by chromatography involves adsorption phenomenon.