Class 9 Chemistry Is Matter Around Us Pure Colloids

Colloids

  • A colloid is a kind of solution in which the size of solute particles is intermediate between those in true solutions and those in suspensions.
  • For Example: - Soap solution, Milk, Ink, Blood and solutions of synthetic detergents.

Class_9_Is_Matter_Around_Us_Pure_Matter_Colloidal_Solutions

  • In a true solution, the solute particles are so small that they cannot scatter or reflect light rays falling on them.
  • In a colloidal solution (or colloid), the particles are big enough to scatter light.
    • If a beam of light is put on a colloidal solution kept in a beaker in a dark room, the path of light beam is illuminated and becomes visible when seen from the side.
    • The path of light beam becomes visible because colloidal particles are big enough to scatter light falling on them in all directions.
  • The scattering of light by colloidal particles is known as Tyndall effect.
  • Tyndall effect can also be observed when a fine beam of light enters a room through a small hole. This happens due to the scattering of light by the particles of dust and smoke in the air.

   Class_9_Is_Matter_Around_Us_Pure_Matter_Tyndall_Effect

  (a) Solution of copper sulphate does not show Tyndall effect,

     (b) Mixture of water and milk shows Tyndall effect.

  • Tyndall effect can be observed when sunlight passes through the canopy of a dense forest. In the forest, mist contains tiny droplets of water, which act as particles of colloid dispersed in air.

 Class_9_Is_Matter_Around_Us_Pure_Matter_Tyndall_Effect_1

  • Note: -
  • A true solution can be distinguished from a colloidal solution by the fact that a true solution does not scatter a beam of light passing through it but a colloidal solution scatters a beam of light passing through it and renders its path visible.
  • Colloids are heterogeneous in nature, though they appear to be homogeneous.

 

Properties of Colloids

  1. A colloid appears to be homogeneous but it is actually it is heterogeneous.
  2. The size of the particles in a colloid is bigger than those in a true solution but smaller than those in a suspension. It is between 1 nm and 100nm in diameter.
  3. The particles of most of the colloids cannot be seen even with microscope.
  4. It scatters a beam of light passing through it.
  • Note:-There is a special technique known as centrifugation can be used to separate the colloidal particles from a colloidal solution.
  • 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.

 

 

Dispersed Phase

Dispersing Medium

Type

Example

Liquid

Gas

Aerosol

Fog, clouds, mist

Solid

Gas

Aerosol

Smoke

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

 

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