Definition, Properties, and Classification of Colloids
Definition of Colloids
Graham was the first man who introduced the term colloids in 1849.
A Colloid may be defined as a substances in a particularly fine state of subdivision, dispersed in another continuous medium giving rise to a large increase in surface area of the dispersed phase.
Thus Colloids are 2 phase heterogeneous system. The dispersed phase and the dispersed medium. e.g. Clay, milk, gum, blood etc.
Classification of Colloids
Colloids may be classified in different ways as follows1. According to affinity of dispersed phase towards dispersed medium, Colloids may be-
A) Layophobic/ Hydrophobic colloids. e.g. metal, gold, sulphide salt etc.
B) Layophilic. e.g. clay minerals, gelatin, gum etc.
2. According to particle shape , colloids may be
A) Sphero colloids. e.g. Glycogen.
B) Linear colloids. Rubber, PVC.
3. According to c h e m i c a l c o m p o s i t i o n , colloids may be
A) Inorganic or mineral colloids. e.g. clay mineral, Fe(OH)2 etc.
B) Organic colloids. e.g. humus, protein etc.
4. According to s t r u c t u r e , colloids are 2 types
A) Molecular colloids (macro). e.g. starch, cellulose etc.
B) Micellar colloids (micro). e.g. Soap, emulsion etc.
Properties of Colloids
Properties of colloids are listed below
1. Particle size.
2. Surface area.
3. Surface charge.
4. Adsorption of cations and anions.
5. Adsorption of water.
7. Osmotic pressure.
9. Faraday tyndall effect.
11. Brownian movement.
12. Catephoresis/ electrocatephoresis.
13. Electro osmosis.
14. Isoelectric point.
17. Zeta potential/ electrostatic potential.
18. Thermodynamic potential.