Question

Differentiate between true solution, colloidal solution and suspension.

Answer 1

The precipitation of colloids by the addition of some suitable electrolyte( induced aggregation) is known as coagulation or flocculation.

Complete answer:
The coagulation of a colloidal solution by an electrolyte does not occur unless and until the electrolyte which is added possesses a definite minimum concentration inside the solution. The minimum concentration of the electrolyte in millimoles that must be added to one litre of the sol so as to bring about complete coagulation is called the flocculation value or coagulation value of the electrolyte for the sol.
Different electrolytes have different coagulation values. As the coagulation value of the electrolyte gets larger, its coagulating or precipitating power reduces. This can be expressed as follows:
$\dfrac{Coagulating\,pwr\,electrolyte\,1}{Coagulating\,pwr\,electrolyte\,2}$
Observations of colloidal solution include:
(i) The ions which carry the charge opposite to that of sol particles are responsible for causing the coagulation of the sol. Such ions are called active ions or flocculating ions.
(ii) Valency of the active ions is inversely proportional to ${{\dfrac{1}{4}}^{th}}$of the coagulating power of an electrolyte. Water is sprinkled before sweeping the room as it helps to coagulate the dust particles. Light particles after coagulation become heavier and settle down due to which it becomes easier to remove them easily.
Colloids generally don't separate on standing. they're not separated by filtration. Suspensions are homogeneous mixtures with particles possessing diameters greater than 1000 nanometer.
In a true solution, the size of particles is less than 1 nanometre, which consist of solute, in the solvent. The solute particle cannot be separated by physical methods like filtration.

Note:
The lyophobic sols are relatively less stable than lyophobic sols. The stability of lyophilic sols is due to the following reasons.
(i) Charge which is present on the colloidal particles
(ii) Solvation of colloidal particles because of greater attractive forces between dispersed phase and dispersion medium.