Question

How are colloids classified on the basis of:
(i) physical states of components,
(ii) nature of dispersed phase and
(iii) interaction between dispersed phase and dispersion medium

Answer 1

The classification of colloids on the basis of (i) physical states of components:

On the basis of physical states of the dispersed phase and dispersion medium, the colloidal solutions classified into eight types of colloidal systems as shown in the following table.
Note: A mixture of gas with another gas is a homogeneous mixture and not a colloidal solution.

Dispersed phase	Dispersion medium	Type of colloidal solution	Example
Solid	Solid	Solid sol	Alloys
Solid	Liquid	Sol	Paints
Solid	Gas	Aerosol	Smoke
Liquid	Solid	Gel	Jelly
Liquid	Liquid	Emulsion	Milk
Liquid	Gas	Aerosol	Mist
Gas	Solid	Solid sol	Pumice
Gas	Liquid	Foam	Soap

(ii) Nature of dispersed phase and dispersion medium:

Colloids are classified into following.
(i) Alcosol
It is a colloidal solution of a solid (dispersed phase) in alcohol (Dispersion medium).
(ii) Aerosol
It is a colloidal solution of a liquid (dispersed phase) in gas (Dispersion medium). Example includes fog.
(iii) Hydrosol
It is a colloidal solution of a solid (dispersed phase) in water (Dispersion medium).
(iv) Benzosol :
It is a colloidal solution with benzene as dispersion medium.
(iii) Interaction between dispersed phase and dispersion medium:
Colloids are classified into lyophilic sols and lyophobic sols.
In lyophilic sols, the dispersed phase particles have great affinity (or love) for the dispersion medium. These sols are reversible. Examples include gum, gelatin, starch, proteins and rubber etc.
In lyophobic sols, the dispersed phase particles have no affinity (or love) for the dispersion medium. These sols are irreversible. Examples include solutions of metals such as gold and silver, metal hydroxides and metal sulphides.
The hydrophobic sols are less stable and easily coagulated than hydrophilic sols because, the stability of hydrophobic sols is due to charge only and the stability of hydrophilic sols is due to charge and solvation/ hydration.