Define the following terms:

A. O/W Emulsion

B. Zeta potential

C. Multimolecular colloids

a) O/W Emulsion: It is a type of emulsion of oil-in-water in which oil is the dispersed phase and water is the dispersion medium.

For example, milk is an emulsion of liquid fat dispersed in water.

Another well-known example is vanishing cream.

Note: Just as in true solution, the substance dissolved is called the solute and the medium in which it is dissolved is called the solvent, similarly in a colloidal system, the terms solute and solvent are replaced by the terms dispersed phase and dispersed medium respectively.

Thus, dispersed phase means the substance distributed in the dispersed medium in the form of colloidal particles

Dispersion medium means the medium in which the substance is dispersed in the form of colloidal particles.

b) Zeta potential

A difference of potential exists between the fixed layer and the diffused layer. This potential difference is known as Zeta potential.

Note: When one type of ions of the electrolyte are adsorbed on the surface of the colloidal particles, it forms a ‘fixed layer’.

It attracts the counter ions from the medium forming a second layer which is mobile and is called ‘diffused layer’.

c) Macromolecular colloids:

When certain substances having big size molecules, called macromolecules, having large molecular masses dissolved in a suitable liquid, they form a solution in which the molecules of the substance, i.e., the dispersed particles have size in the colloidal range. Such substances are called macromolecular colloids.

Examples: Starch, cellulose, proteins, enzymes and gelatin.