Colloidal particles

Colloids: A colloid is a solution in which the size of solute particles is bigger than that of a true solution but smaller than that of a suspension. Thus, colloids appear to be homogeneous but actually they are heterogeneous when observed through a high-power microscope.

So, colloids are not true solutions. Some examples of colloidal solutions are: starch solution, milk, ink, blood, soap solution etc.

Characteristics of Colloids
(i) A colloid appears to be homogeneous but actually it is heterogeneous.

(ii) The size of particles in a colloid is bigger than those in a true solution but smaller than those in a suspension. It is between 10-9 m to 10-6 m (1 nm to 1000 nm) in diameter.

(iii) A colloidal solution can not be separated by filtration through ordinary filter paper.

(iv) Particles of a colloid do not settle down when left undisturbed, i.e., a colloid is quite stable.

(V) Colloids are big enough to scatter a beam of light passing through it.

Note: A colloidal solution appears homogeneous but actually it is heterogeneous.