Colloids
a homogeneous non-crystalline substance consisting of large molecules or ultramicroscopic particles of one substance dispersed through a second substance. Colloids include gels, sols, and emulsions; the particles do not settle, and cannot be separated out by ordinary filtering or centrifuging like those in a suspension.
Dispersed Phase:
The phase which is dispersed or scattered through the dispersion medium is called Dispersed phase or discontinuous phase.
Dispersion Medium:
The phase in which the scattering is done is called the dispersion medium or continuous medium
Lyophobic and Lyophilic Colloids:
Those substances whose colloidal solution cannot be prepared by bringing them in contact with a solvent are
called Lyophobic (disliking, fearing or hating a liquid).
On the other hand those substances whose colloidal solutions can be prepared by bringing them in contact with a liquid solvent are called lyophilic colloids (loving a solvent).
Emulsions:
● Emulsion of oil in water:
Those emulsions in which the dispersed phase is oil and water is the dispersion medium. These emulsions are generally represented as O in W emulsions. Examples are
milk, vanishing cream etc.
● Emulsions of water in oil:
Those emulsions in which the dispersed phase is water while oil is the dispersion medium. These emulsions are generally represented as W in O emulsions. Examples are
butter, ice cream etc.
Preparation of colloidal solution
Bredig's method:
An electric arc is struck between two metallic electrodes immersed in a dispersion medium. The arc produced
evaporates the metal which on further condensation produces particles of colloidal size.
Peptization:
Process of converting a precipitate into colloidal sol by shaking it with electrolyte
in a dispersion medium.
Hardy Schulze Rule:
> Ion carrying charge opposite to the colloidal particle has the capacity to coagulate the colloid.
> Greater the valency of ion, greater will be the coagulating power.
Gold Number:
The minimum amount of lyophilic colloid in milligrams which can prevent the coagulation of 10 ml gold sol against 1 mL of 10% NaCl solution.
Chemical methods:
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