What is the difference between multimolecular and macromolecular colloids? Give one example of each. How are associated colloids different from these two types of colloids?
Explanation Multimolecular colloids: On dissolving into dispersion medium, a large number of atoms or small molecules of dispersed phase aggregate together to form species having size of the colloidal order range. Colloids so formed are called as multi-molecular colloids e.g. a gold sol may contain dispersed phase particles of various sizes having from 100 to 1000 Au atoms each, similarly sulphur sol consists of dispersed phase particles containing 1000 or more of molecules. Macromolecular colloids: Macromolecules like proteins, gum, starch, gelatine etc. form such colloids as their size falls in colloidal order range. When they are added to some suitable medium they form macromolecular colloids. These colloids are quite stable and resemble with true solutions in many aspects. Man-made macromolecules are polythene, nylon, polystyrene, synthetic rubber etc. they also fall in this category. Associated colloids (Micelles): Some substances like soaps and detergents behave as electrolytes or crystalloids at low concentrations and form colloids at higher concentrations due to formation of aggregates or micelles, so they are also called as associated colloids. Minimum concentration and minimum temperature above which micelle formation occurs are known as CMC (critical micelle concentration) and Kraft temperature (Tk) respectively. On dilution those colloids revert back to individual ions example for soaps CMC is 10–4 to 10–3 mole per litre. A micelle generally contains 100 or more soap or detergent molecules. Final Answer Multimolecular colloids are those which in dissolving into dispersion medium forms a large number of atoms or small molecules of dispersed phase aggregate together, having size of the colloidal order range. Macromolecules like proteins, gum, starch, gelatine etc. form such colloids as their size falls in colloidal order range. When they are added to some suitable medium they form macromolecular colloids. Some substances like soaps and detergents behave as electrolytes or crystalloids at low concentrations and form colloids at higher concentrations due to formation of aggregates or micelles.
