Phases of colloids and Their classification
(1) Phases of colloids: We know that a colloidal solution is of heterogeneous nature. It consists of two phases which are as follows
(i) Internal phase or Dispersed phase (Discontinuous phase) : It is the component present in small proportion and is just like a solute in a solution. For example in the colloidal solution of silver in water (silver acts as a dispersed phase)
(ii) External phase or Dispersion medium (continuous phase) : It is generally component present in excess and is just like a solvent in a solution. For example, in the colloidal solution of silver in water. Water act as a dispersion medium.
(2) Classification of colloids : The colloids are classified on the basis of the following criteria
(i) Classification based on the physical state of the dispersed phase and dispersion medium : Depending upon the physical state of dispersed phase and dispersion medium whether these are solids, liquids or gases, eight types of colloidal systems are possible.
Table : 14.3 Different types of colloidal systems
| Dispersed phase | Dispersion Medium | Colloidal System | Examples |
| Liquid | Gas | Aerosol of liquids | Fogs, clouds, mists, fine insecticide sprays |
| Solid | Gas | Aerosol of solids | Smoke, volcanic dust, haze |
| Gas | Liquid | Foam or froth | Soap lather. Lemonade froth, foam, whipped cream, soda water |
| Liquid | Liquid | Emulsions | Milk, emulsified oils, medicines |
| Solid | Liquid | Sols | Most paints, starch in water, proteins, gold sol, arsenic sulphide sol, ink |
| Gas | Solid | Solid foam | Pumice stone, styrene rubber, foam rubber |
| Liquid | Solid | Gels | Cheese, butter, boot polish, jelly, curd |
| Solid | Solid | Solid sols (coloured glass) | Ruby glass, some gem stones and alloys |
(ii) Classification based on Nature of interaction between dispersed phase and dispersion medium: Depending upon the nature of interactions between dispersed phase and the dispersion medium, the colloidal solutions can be classified into two types as (a) Lyophilic and (b) Lyophobic sols.
(a) Lyophilic colloids (water loving):“The colloidal solutions in which the particles of the dispersed phase have a great affinity for the dispersion medium, are called lyophilic collodis.”
(b) Lyophobic colloids(water hateing): “The colloidal solutions in which there is no affinity between particles of the dispersed phase and the dispersion medium are called lyophobic colloids.”