*Colloidal solution or Colloids :
A heterogeneous solution in which the particle size is in between 10–7cm to 10–5cm such that the solute particles neither dissolve nor settle down in a solvent, is called colloidal solution. The components of a colloidal solutions are the dispersed phase and the dispersion medium. The solute- like component or the dispersed particles in a colloidal form of the dispersed phase, and the component in which the dispersed phase is suspended is known as the dispersing medium.
*Properties of colloids :
1.The size of particles of a colloid is too small to be individually seen by naked eyes.
2.They do not settle down when left undisturbed, that is colloid is quite stable.
3.They can not be separated from the mixture by the process of filteration. But, special technique of separation known as centrifugation can be used to separate the colloidal particles.
4.Colloidal solutions are not transparent, but translucent in nature.
5.The particles of a colloidal solution scatter light i.e. when strong beam of light is passed through the colloidal solution, the path of beam becomes visible.
Dispersed phase :- It is the component which is present in small proportion and consists of particles of colloidal dimensions (10–9 m to 10–7 m).
Dispersion medium :- It is the component which is present in excess and acts as a medium in which colloidal particles are dispersed.
Common examples of colloids
Dispersed 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
Solid Solid Solid Sol Coloured gemstone,milky glass
*Brownian movement of colloids :-
The colloidal particles are moving at random in a zigzag motion in all directions. This type of zig- zag motion of colloidal particles is called Brownian movement. The brownian movement is caused by the collision (hitting) of the colloidal particle with the molecules of the dispersion medium.
*Tyndall effect :
The phenomenon due to which the path of light becomes visible, due to scattering of light by the colloidal particle is called tyndall effect.
Example :
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.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 colloids dispersed in air.