. Explain how the phenomenon of adsorption finds application in each of the following processes


Explain how the phenomenon of adsorption finds application in each of the following processes

(i) Production of vacuum

(ii) Heterogeneous catalysis

(iii) Froth floatation process

                                                         OR

Define each of the following terms

(i) Micelles

(ii) Peptization

(iii) Desorption

Best Answer

(i) Production of Vacuum: Adsorption can be successfully applied to create conditions of high vacuum. For this a bulb of charcoal cooled in liquid air, is connected to vessel which has already been exhausted as far as possible by vacuum pump. The remaining traces of air inspite of low pressure are adsorbed by the charcoal almost completely.

(ii) Heterogeneous Catalysis: There are many gaseous reactions of industrial importance involving solid catalyst. Manufacture of ammonia using iron as a catalyst, manufacture of H2SO4 by contact process using V2O5 catalyst and use of finely divided nickel in the hydrogenation of vegetable oils are the excellent examples. The gaseous reactants are adsorbed on the surface of the solid catalyst. As a result, the concentration of the reactants increases on the surface of the catalyst and hence the rate of reaction increases.

(iii) Froth Floatation Process: In froth floatation process the powdered ore is mixed with water. It is then mixed with pine oil (a frother). The oil particles are adsorbed on the surface of ore particles. Now, a stream of air is blown through the mixture from below when froth is formed at the water surface. The ore particles stick to the bubbles of the air rises to surface along with the foam while the gangue particles which are wetted by water settle at the bottom. The foam is separated out and is collected and in the course, the ore particles also settle down

                                                                                                        OR

(i) Micelles: There are some substances which at low concentration behave as normal strong electrolytes but at higher concentration exhibit colloidal behaviour due to formation of aggregated particles. The aggregated particles thus formed are called micelles. The formation Examination Papers 181 of micelles takes place only above a particular temperature called Kraft temperature and above a particular concentration called critical micelle concentration (CMC). Surface active agents such as soap and synthetic detergents belong to this class.

(ii) Peptization: The process of converting a precipitate into colloidal sol by shaking it with dispersion medium in the presence of a small amount of suitable electrolyte is called peptization. During peptization, the precipitate absorbs one of the ions of the electrolyte on its surface. This causes development of positive or negative charge on precipitates, which ultimately break up into particles of colloidal dimension.

(iii) Desorption: The process of removing an adsorbed substance from a surface on which it is adsorbed is called desorption.

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