What is colloid?
 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.
Properties of a
colloid
• A colloid is a heterogeneous mixture.
• The size of particles of a colloid is too small to be
individually seen by naked eyes.
• Colloids are big enough to scatter a beam of light passing
through it and make its path visible.
• They do not settle down when left undisturbed, that is, a
colloid is quite stable.
• They cannot be separated from the mixture by the process
of filtration. But, a special technique of separation known as centrifugation can
be used to separate the colloidal particles.
The components of a colloidal solution are the dispersed
phase and the dispersion medium. The solute-like component or the dispersed
particles in a colloid form the dispersed phase, and the component in which the
dispersed phase is suspended is known as the dispersing medium. Colloids are classified
according to the state (solid, liquid or gas) of the dispersing medium and the dispersed
phase. A few common examples are given in Table. From this table you can see
that they are very common everyday life.
Common Examples of Colloids
|
Dispersing Phase |
Dispersing Medium |
Type |
Example |
|
Liquid |
Gas |
Aerosol |
Fog, Clouds, Mist |
|
Solid |
Gas |
Aerosol |
Smoke, Automobile Exhaust |
|
Gas |
Liquid |
Foam |
Shaving Cream |
|
Liquid |
Liquid |
Emulsion |
Milk, Face Cream |
|
Solid |
Liquid |
Sol |
Milk of Magnesia, Mud |
|
Gas |
Solid |
Foam |
Foam, Rubber, Sponge, Pumice |
|
Liquid |
Solid |
Gel |
Jelly, Cheese, Butter |
|
Solid |
Solid |
Solid sol |
Coloured Gemstone, Milky Glass |