Class 12 Chemistry Surface Chemistry Properties of Colloids

Properties of Colloids

Colligative Properties-

The particles in colloids are bigger aggregates than those in a true solution. So, the number of particles in a colloid is lesser than a true solution of the same concentration. The values of colligative properties (osmotic pressure, lowering of vapour pressure, depression in freezing point, elevation in boiling point) are of small order as compared to values shown by true solution at same concentration.

Tyndall effect-

Tyndall effect is the scattering of the light by the particles present in the colloidal solution when viewed at right angles to the passage of light.

It is observed only when-

  • The diameter of the dispersed particles is not much smaller than the wavelength of light used
  • The refractive indices of the dispersed phase and dispersed medium have a large difference
  • This effect was used to make an ultramicroscope and differentiate between true solution and colloids.


The colour of the colloidal solution depends on the wavelength of the light scatter by the dispersed particles, size and nature of the dispersed particles and the manner in which it is viewed.  Example- Finest gold sol is red in colour and as the size of the particle keeps increasing its colour changes to blue, then purple and finally gold.

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