Explain how

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

(ii) Heterogeneous catalysis: If the catalysts and reactants are present in different phase, the process of catalysis is called as heterogenous catalysis. Adsorption of reactants on the solid surface of the catalysts increases the rate of reaction.

(iii) Froth Floatation process: This method is used for removing gangue from sulphide ores. In this powdered ore is mixed with collectors (e.g. pine oil, fatty acids etc.) and froth stabilizers (e.g. cresols, aniline) which enhance non-wet ability of the mineral particles and froth stabilisation respectively. In this process, sulphide ore is concentrated by using pine oil which adsorbs the ore particles and impurities are wetted by water which settle at the bottom. As a result of which ore comes with froth and gangue remain in the solution.

OR

(i) Micelles: When soaps and detergents are added to water, a cluster of charged particles is formed by the aggregation of variety of molecules. This formed cluster is called micelle.

In other words, Micelles are associated colloids which show colloidal behaviour at high concentration and act as strong electrolytes at low concentration.

(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 electrolyte is called Peptization.

In other words, the process of converting a fresh precipitate into colloidal particles by shaking it with the dispersion medium in the presence of a small amount of a suitable electrolyte is called peptization.

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

In other words, the process of removal of adsorbed substance from the surface of a solid or a liquid by heating or by reducing pressure is called desorption.