Write the dispersed phase and dispersion medium of the following colloidal systems:

(i) Smoke

(ii) Milk

OR

What are lyophilic and lyophobic colloids? Which of these sols can be easily coagulated on the addition of small amounts of electrolytes?

(i) Dispersed phase in smoke - Solid.

Dispersion medium in smoke – Gas.

(ii) Dispersed phase in milk - Fats (liquid).

Dispersion medium in milk - Water (liquid).

OR

‘Philic’ means loving and ‘phobic’ means hating.

Lyophilic colloids are therefore, colloidal solutions in which dispersed phase has great affinity for dispersion medium. These solutions are quite stable and are reversible in nature. Eg. sols of gum, gelatine, starch, proteins and certain polymers in organic solvents.

Similarly, lyophobic colloids are colloidal solutions in which dispersed phase has very little affinity for the dispersion medium.

Such solutions are unstable and are irreversible in nature. Eg. Sols of metals and their insoluble compounds like sulphides and oxides.

Lyophobic colloids can be easily coagulated because on addition of small amount of electrolyte, the charge on colloidal particles is removed, due to which the particles will come closer to each other and under the influence of gravity, they combine to form a cluster and settle down.