Applications of Adsorption | Class XII

Adsorption finds extensive applications both in research laboratory and in industry. A few applications are briefly described below

(i) In preserving vacuum. In Dewar flasks, activated charcoal is placed between the walls of the flask so that any gas which enters into the annular space either due to glass imperfection or diffusion through glass is adsorbed.

(ii) In gas masks. All gas masks are devices containing suitable adsorbent so that the poisonous gase, present in the atmosphere are preferentially adsorbed and the air for breathing is purified.

(iii) In clarification of sugar. Sugar is decolorised by treating sugar solution with charcoal powder. latter adsorbs the undesirable colours present.

(iv) In chromatographic analysis. The selective adsorption of certain substances from a solution by , particular solid adsorbent has helped to develop a technique for the separation of the components of the mixture. This technique is called chromatographic analysis. For example, in column chromatography, a long and wide vertical tube is filled with a suitable adsorbent and the solution of the mixture poured from the top and then collected one by one from the bottom.

(v) In heterogeneous catalysis. The action of certain solids as catalysts is best explained in terms of adsorption. The theory is called adsorption theory. According to this theory, the gaseous reactants are adsorbed on the surface of the solid catalyst. As a result, the concentration of the reactants increase, on the surface and hence the rate of reaction increases, e.g., in the manufacture of ammonia using iron as catalyst, in the manufacture of sulphuric acid by contact process using V2O5 as catalyst and use of finely divided nickel in the hydrogenation of oils. The theory is also able to explain the greater efficiency of a catalyst in the finely divided state, the action of catalytic poisons etc.

(vi) In adsorption indicators. Various dyes, which owe their use to adsorption, have been introduced. indicators particularly in precipitation titrations. For example, KBr is easily titrated with AgNO3 using eosin as an indicator.

(vii) In softening of hard water. The use of ion exchangers for softening of hard water is based upon the principle of competing adsorption just as in chromatography.

(viii) In removing moisture from air in the storage of delicate instruments. Such instruments which may be harmed by contact with the moist air, are kept out of contact with moisture using silica get. Silica gel is the most commonly used dehumidizer, i.e., to adsorb humidity or moisture from the air.

(ix) In the separation of inert gases. Different inert gases are adsorbed to different extents at different temperatures on coconut charcoal. This forms the basis of their separation from a mixture.

(x) In froth floatation process. When sulphide ore is shaken with pine oil and water, the ore particles are adsorbed on the froth that floats and the gangue particles (silica, earthy matter etc.) settle down in the tank. The method is known as froth floatation process for concentration of sulphide ores.

(xi) In paint industry. The paint should not contain dissolved gases as otherwise the paint does not adhere well to the surface to be painted and thus will have a poor covering power. The dissolved gases are, therefore, removed by suitable adsorbents during manufacture. Further, all surfaces are covered with layers of gaseous, liquid or solid films. These have to be removed before the paint is applied. This is done by suitable liquids which dissolve these films. Such liquids are called wetting agents. The use of spirit as wetting agent in furniture polishing is well known.

(xii) In dyeing. In dyeing, clothes are first kept dipped in a mordant (generally, alum) and then in the solution of the dye. The mordant is first adsorbed on the clothes and then the dye is adsorbed on the mordant. In other words, mordant adheres well both to fibre and the dye. If this is not done, uneven dying would take place.

(xiii) In water conservation. In countries like Australia where there is acute scarcity of water during summer, layer of stearic acid etc. is sprayed over the lakes and other water reservoirs. It is adsorbed on the surface of water thereby minimising the loss of water by evaporation.

(xiv) In curing diseases. Some drugs can adsorb the germs on them and hence kill them and save us from diseases.

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