Define the following terms:

a) Brownian movement

b) Peptization

c) Multimolecular colloids

a) Brownian movement –the phenomenon was discovered by Robert Brown in 1927. It is defined as the random continuous motion of the particles which are suspended in a liquid or in a gas. It is caused due to the collision of the particles with each other and with the molecules of the surrounding medium due to their random movement with varying velocities. The movement of particles is continuously and they move in a zigzag manner.

b) Peptization – It is the process of conversion of a fresh precipitate into a colloidal solution by shaking it with the dispersion medium in the presence of an electrolyte.The electrolyte which is used in thisprocess is called a peptizing agent. For example, a precipitate of AgCl on shaking with dilute solution of adsorbsions and get peptized to colloidal particles of the type [AgCl].

c) Multimolecular colloids - The colloidal particles are formed by the aggregation of atoms or small molecules having diameter less than 1 nm. The molecules in the aggregated form are held together byforces of attraction like van der Waal’s. For instance, gold sol and sulphur sol.