COLLOID True solution The solute particles consist of individual molecules or ions e.g. sugar or salt in water. Suspension Particles contain more than one molecule and are large enough to be seen by the eye or at least under a microscope. Colloidal dispersions Particles may contain more than one molecule but are not large enough to be seen in a microscope, dimension = (5- 200) nm. e.g. macromolecules (starch and proteins). Solutions of these substances therefore exhibit colloidal behavior, and although they may involve single molecules, they are conveniently classified as colloidal systems. Disperse phase is refers to the particles that are present in the dispersion medium. Both the disperse phase and the dispersion medium may be solid, liquid or gaseous. Table 1: Types of colloidal systemsDispersion Medium Disperse Phase Name of System Examples Gas Liquid Aerosol Fog, mist, clouds Gas Solid Aerosol Smoke Liquid Gas Foam Whipped cream Liquid Liquid Emulsion Milk, mayonnaise Liquid Solid Sol Gold in water Solid Liquid Gel Jelly Solid Solid Gel Ruby glass, gold in Solid Gas Solid foam Pumice, styrofoam TYPE OF SOLS Colloidal dispersions of solids in liquids (sols) can be divided into two types: 1. Lyophobic Sols •Also called hydrophobic sols (if the dispersion medium is water). •Relatively unstable. •The addition of electrolytes to lyophobic sols frequently causes coagulation and precipitation. 1
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