Surface Chemistry

Surface Chemistry

Question

Define the following terms giving an example of each:

(i) Associated colloids

(ii) Lyophilic sol

(iii) Adsorption

Answer

(i) Associated colloids: Associated colloids are those colloids which behave as normal strong electrolytes at low concentrations but exhibit colloidal properties at higher concentrations due to the formation of aggregated particles thus formed are micelles. For e.g. grease droplet surrounded by stearate ions.

(ii) Lyophilic sol: Lyophilic means liquid-loving colloidal sols directly formed by mixing substances like gum, gelatine etc. with a suitable liquid (the dispersion medium) are called lyophilic sols. If the dispersion medium is separated from dispersed phase (say by evaporation), the sol can be reconstituted by simply remising with the dispersion medium that is why these sols are also known as reversible sols.

(iii) Adsorption: The accumulation of molecular species at the surface rather than in the bulk of a solid or liquid is known as adsorption. The molecular species which accumulates on the surface is termed as adsorbate and the material on the surface of which the adsorption takes place is called adsorbent.

For the e.g. aqueous solution of raw sugar, when passed over beds of animal charcoal, becomes colourless as the colouring substances are adsorbed by the charcoal.

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