Coagulation Of Colloidal Solutions

Let’s start by understanding what is Coagulation first. Well, according to the general definition, coagulation is one of the various properties exhibited by colloidal solutions. A colloid is a heterogeneous mixture of one substance of very fine particles (dispersed phase) dispersed into another substance (dispersion medium).

Substances like metals, their sulfides etc. cannot be simply mixed with the dispersion medium to form a colloidal solution. Some special methods are used to make their colloidal solutions. Such kind of sols is known as lyophobic sols. These kinds of colloidal solutions always carry some charge on them. Charge present on the colloidal sols determines their stability. If by any chance we can remove the charge present on the sol, the particles get closer to each other and they accumulate to form aggregates and precipitate under the action of gravity. This process of accumulation and settling down of particles is further known as coagulation or precipitation.

Coagulation Techniques:

The process of coagulation can be carried out in the following ways:

1. By electrophoresis: In this method, the colloidal particles are forced to move towards the oppositely charged particles and then they are discharged and collected at the bottom.

2. By mixing two oppositely charged sols: In this type of coagulation equal amounts of oppositely charged particles are mixed, they cancel out their charges and then precipitate.

Coagulation by mixing two oppositely charged sols

Fig. Coagulation by mixing two oppositely charged sols

 3. By boiling: Whenever we boil a sol, the molecules of the dispersion medium start colliding with each other and with the surface, this, in turn, disturbs the adsorption layer. This reduces the charge on the sol due to which the particles settle down.

4. By persistent dialysis: Under the persistent dialysis parts of electrolytes are removed completely and the sol loses its stability and ultimately coagulates.

Coagulation by Persistent Dialysis

Fig. Coagulation by Persistent Dialysis

Coagulation of lyophilic solutions:

Stability of lyophilic sol depends on the following two factors

  • Charge
  • Solvation

When the above two factors are removed then only lyophilic sols can be coagulated. This can be done by either adding an electrolyte or a suitable solvent.

This was just a brief layout of coagulation of lyophilic and lyophobic colloids. To know more about the process of coagulation, you can register with Byju’s and download our app.


Practise This Question

Among the following electrolytes, which is the most effective coagulating agent for Sb2S3 solution?