Question

Give four uses of adsorption.

Explain two applications of adsorption.

Answer 1

1. Catalysis (Heterogeneous catalysis):
   a. The solid catalysts are used in many industrial manufacturing processes.
   b. For example, iron is used as a catalyst in the manufacturing of ammonia, platinum in the manufacturing of sulphuric acid, H₂SO₄ (by contact process) while finely divided nickel is employed as a catalyst in the hydrogenation of oils.
2. Gas masks:
   a. It is a device that consists of activated charcoal or a mixture of adsorbents.
   b. It is used for breathing in coal mines to avoid inhaling of poisonous gases.
3. Control of humidity:
   Silica and alumina gels are good adsorbents of moisture.
4. Production of high vacuum:
   a. Lowering of temperature at a given pressure, increases the rate of adsorption of gases on charcoal powder. By using this principle, a high vacuum can be attained by adsorption.
   b. A vessel evacuated by a vacuum pump is connected to another vessel containing coconut charcoal cooled by liquid air. The charcoal adsorbs the remaining traces of air or moisture to create a high vacuum.
5. Adsorption indicators:
   The adsorption is used to detect the endpoint of precipitation titrations. Dyes such as eosin, fluorescein are used as indicators. e.g.
   a. A solution of sodium chloride containing a small amount of fluorescein is titrated against silver nitrate solution.
   \[\ce{\underset{\text{Sodium chloride}}{NaCl} + \underset{\text{Silver nitrate}}{AgNO3} -> \underset{\text{White ppt.}}{AgCl} + \underset{\text{Sodium nitrate}}{NaNO3}}\]
   b. When chloride ions are over, fluorescein is adsorbed on white silver chloride precipitate and hence, red colour is developed.
   c. Thus, colour changes from pale yellow to reddish pink at the endpoint.
6. Separation of inert gases:
   a. In a mixture of noble gases, different gases adsorb to a different extent.
   b. Due to selective adsorption principle, gases can be separated on coconut charcoal.
7. Froth floatation process:
   a. A low-grade sulphide ore is concentrated by separating it from silica and other earthy matter using pine oil as a frothing agent.
   b. Hydrophobic pine oil preferentially adsorbs sulphide ore which is taken up in the froth.
8. Chromatographic analysis:
   a. It is based on selective adsorption of ions from solution using powdered adsorbents such as silica or alumina gel.
   b. It has several industrial and analytical applications. Other applications include surface area determination, purification of water, etc.