(i) Explain the meaning of the statement. ‘Adsorption is a surface phenomenon.’
(ii) State two features of chemical adsorption which are not found in physical adsorption.
(iii) Explain the terms with suitable examples: (i) Gel, (ii) Aerosol and (iii) Hydrosol.
i)The accumulation of molecular species at the surface rather than in the bulk of a solid or liquid is termed adsorption.
Adsorption is essentially a surface phenomenon. Solids, particularly in finely divided state, have large surface area and therefore, charcoal, silica gel, alumina gel, clay, colloids, metals in finely divided state, etc. act as good adsorbents.
ii)
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Physisorption |
Chemisorption |
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It arises because of van der |
It is caused by chemical bond |
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It is not specific in nature. |
It is highly specific in nature. |
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It is reversible in nature |
It is irreversible. |
iii)
i) gel: a solution having a liquid as dispersion medium and a solid as dispersed phase is called gel. For example gum Arabic, agar.
ii) Aersol: A colloidal solution having a gas as the dispersion medium and a solid as dispersed phase is called an aerosol. For example fog.
iii) Hydrodol: A colloidal solution having water as the dispersion medium and a solid as the dispersed phase is called a hydrosol. For example starch sol, gold sol.
