Question

Define the Brownian movement. What is the cause of the Brownian movement in colloidal particles? How is it responsible for the stability of the colloidal solution?

Answer 1

Sols or colloidal sols are made up of thousands of particles. These particles have kinetic energy which causes kinetic motion. This kinetic motion opposes the force of gravity.

Complete step by step solution:
The colloidal particles are seen continuously moving in a zig-zag way when the colloidal sol was viewed through an ultramicroscope. In 1827, this observation was done by Robert Brown where he collected some pollen grains, suspended it in the water and then he observed it under a microscope. He observed some movement and named it the Brownian movement. So, we can say that the Brownian movement is the continuous zig-zag movement of the colloidal particles in a colloidal sol.
We can define the cause of the Brownian movement as the fact that the molecules of the dispersion medium due to their kinetic energy of the molecules causing kinetic motion strike against the colloidal particles from all sides with different forces which causes their movement. But the colloidal particles are heavier, they move at slow speed.
The importance of the Brownian movement is:
It does not allow the colloidal particle to settle down as it opposes the force of gravity. Thus, it is responsible for the stability of the colloidal solution.
It can also be used for the determination of Avogadro's number.

Note: The Brownian movement depends upon the size of the colloidal particle and viscosity of the sol and does not depend on the nature of the colloidal sol. So, we can say that the smaller the size and the lesser the viscosity, the greater will be Brownian movement.