Thursday, January 31, 2008

IIt JEE Revision - Emulsions, Surfactants and Micelles

JEE syllabus

Elementary ideas of emulsions, surfactants and micelles (only definitions and examples).


Emulsion is a liquid dispersed in a liquid.

Any two immiscible liquids form an emulsion.

For example, milk is a naturally occuring emulsion in which particles of liquid fats are dispersed in water.

Since two immiscible liquids do not mix well, the emulsion is generally unstable and separation of liquids may take place on standing for some time.

Emulsifiers are substances which are added to make emulsions more stable.

Emulsifiers reduce the interfacial tension between the two liquids.

Two types of emulsions: Oil in water and water in oil.

Identifications of two types of emulsions:
Dilution test: If on addition of water, the emulsion becomes dilute, it means it is oil in water emulsion.

Dye test: An oil soluble dye is used and if the whole solution becomes coloured it is water in oil emulsion. If only drops become coloured, it is oil in water emulsion.

Any substance which can decrease the surface tension of water to a large extent is known as surfactant. Examples of soap and detergents. Such substances have larger concentrations at the surface of water as compared to the bulk of the solution.

Surfactants in solution are often association colloids, that is, they tend to form aggregates of colloidal dimensions, which exist in equilibrium with the molecules or ions from which they are formed. Such aggregates are termed micelles.

No comments: