Colloidal systems (colloidal solutions) are heterogeneous in nature and consist of following two phases:
(i) Dispersed phase: The substance present in the form of colloidal particles in a colloidal system constitutes the dispersed phase. Thus, the dispersed phase may be defined as the phase constituting the colloidal particles. For example, in a colloidal solution of ferric hydroxide in water, the ferric hydroxide particles are of colloidal size and constitute the dispersed phase.
(ii) Dispersion medium: The medium in which the colloidal particles are dispersed is called dispersion medium. For example, in the colloidal solution of ferric hydroxide in water, water is the dispersion medium.
Classification Based on Physical State of Dispersed Phase and Dispersion Medium.
Depending upon the physical state of the dispersed phase and dispersion medium, eight types of colloidal systems are possible. These are described in the table given below:
|
S.No.
|
Dispersed phase
|
Dispersion medium
|
Common name of the system
|
Examples
|
|
1.
|
Solid
|
Solid
|
Solid sol
|
Gems, ruby glass, coloured glasses, pigmented plastics etc.
|
|
2.
|
Solid
|
Liquid
|
Sol
|
Gold sol, sulphur sol, ferric hydroxide sol, As2S3 sol, ink, most of the paints, starch dispersed in water, muddy water etc.
|
|
3.
|
Solid
|
Gas
|
Aerosol of solids
|
Smoke, dust etc.
|
|
4.
|
Liquid
|
Solid
|
Gel
|
Cheese, butter, boot polish, jellies etc.
|
|
5.
|
Liquid
|
Liquid
|
Emulsion
|
Milk, emulsified oils, medicines etc.
|
|
6.
|
Liquid
|
Gas
|
Aerosol of liquids
|
Fog, mist, clouds, Liquid sprays etc.
|
|
7.
|
Gas
|
Solid
|
Solid foam
|
Pumice stone, styrene foam, foam rubber etc.
|
|
8.
|
Gas
|
Liquid
|
Foam or Froth
|
Lemonade froth, soap lather, shaving cream foam etc.
|
Table: Types of Colloidal Systems
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