4. 4
LEARNING OBJECTIVE
At the end of this lecture student will be able to
understand:
1. Classification of dispersed systems
2. General characteristics, size & shapes of colloidal
particles
3. Optical, kinetic & electrical properties
4. Effect of electrolytes, coacervation, peptization&
protective action
6. 6
Colloids
A colloid is a substance in which microscopically
dispersed insoluble particles are suspended
throughout another substance.
A substance being dispersed- Dispersed Phase
The substance in which it is dispersed- Continuos
Phase
8. 8
CLASSIFICATION OF COLLOIDS
I. Classification based on physical state of Dispersed phase and
Dispersion medium
II. Classification based on electrical charge on dispersion phase
III. Classification based on Appearance of the colloids
IV. Classification based on molecular size of the dispersed phase
V. Classification based on the interaction or affinity of two phases
9. 9
I. Classification based on physical state of Dispersed phase
and Dispersion medium
Sr no. Dispersed
phase
Dispersion
medium
Name of colloidal
solution
Examples
1 Gas Liquid Foam Soap lather, soda water, froth on
beer
2 Gas Solid Solid foam Cake, Bread, Pumice stone lava
3 Liquid Gas Aerosol Mist, fog, clouds
4 Liquid Liquid Emulsion Milk, cream, butter, oil in water
5 Liquid Solid Gel Curd, cheese, Jellies
6 Solid Gas Solid Aerosol Smoke, dust
7 Solid Liquid Sols Paints, gold sol, inks
8 Solid Solid Solid sols Alloys, coloured glass, gem
stones
10. 10
II. Classification based on electrical charge on dispersion
phase
Two types:
1. Positive colloids
When dispersed phase in the colloidal solution carries a positive charge, it
is known as Positive colloids.
Examples: Metal hydroxides like Fe (OH)3, Al(OH)3, TiO2, Methylene blue
sols etc.
2. Negative colloids
When dispersed phase in the colloidal solution carries a negative charge, it
is known as Negative colloids.
Examples: AS2S3 sol, Cu or Ag sol.
11. 11
III. Classification based on Appearance of the colloids
Sols
When the colloidal solution appears as fluid - Sol.
The sols are generally named after dispersion medium.
When the dispersion medium is water, -Hydrosol or Aquosol.
When the dispersion medium is alcohol and benzene, -Alcosol and Benzosol
respectively.
Gels
When the colloidal has solid -Gel.
Some e.g. of gels are: jelly, butter, cheese, curd.
12. 12
IV. Classification based on molecular size of the dispersed phase
Divided into three types:
a) Multimolecular colloids
Small molecules having diameter less than 10-7 cm
The particles are held by weak Vander waal’s forces.
Eg. Gold sol , Sulphur sol
b) Macro Molecular colloids
sufficiently large in size enough to be of colloidal dimensions.
These are called Natural polymers.
examples are starch, cellulose and proteins.
polymers are polythene, polystyrene, nylon and plastic.
13. 13
c) Association colloids
These are normal electrolytes at low concentrations but behave as colloids at
higher concentration.
Association colloids are also referred as Micelles.
The examples of association colloids are; Sodium stearate, Soaps, higher
alkyl sulphonates polythene oxide etc.
14. 14
V. Classification based on the interaction or affinity of two phases
Classified in terms of the attraction between the dispersed phase and dispersion
medium as:
a) Lyophilic colloids
b) Lyophobic colloids
Lyophilic colloids Lyophobic colloids
The dispersed phase has a
great affinity or love for the
dispersion medium
The dispersed phase has no
affinity or hates the
dispersion medium
Lyophilic colloids are also
called intrinsic colloids.
These are also referred as
extrinsic colloids
Generally self stabilized The lyophobic colloids are
relatively unstable
Reversible in nature and are
heavily hydrated.
They are irreversible and are
stabilized by adding small
amount of electrolyte.
Examples of Lyophilic
Colloids are Starch, Gelatin,
Rubber, Protein Etc.
Examples are sol of metals
like au, ag sol of metal
hydroxide like al(oh)3,
fe(oh)3, etc and sol of metal
sulphites like AS2S3.
