Question

Which of the following is/are lyophobic colloids?
a.) Gold sol
b.) ${\text{A}}{{\text{s}}_2}{{\text{S}}_3}$ sol
c.) ${\text{Fe(OH}}{{\text{)}}_3}$sol
d.) Starch sol

Answer 1

Hint: As the name suggests ‘lyo’ means liquid and ‘phobic’ means fearing. Certain colloidal solutions have very low affinity between the dispersed phase and dispersion medium.

Complete step-by-step answer:
A colloid is a mixture in which one of the substances is split into very minute particles which are dispersed throughout a second substance. The substance which is dispersed is called a dispersed phase whereas the one in which the first substance is distributed is called a dispersion medium. On basis of the interactions between dispersion medium and dispersed phase, colloids are of two types –

Lyophobic colloid
If the dispersed phase has very little or no affinity for the dispersion medium, the type of colloid is called a Lyophobic colloid.

Lyophilic colloid
If the dispersed phase has a good affinity for dispersion medium, the type of colloid is called a lyophilic colloid.
Metals like Au, As and metal hydroxides often form lyophobic colloids. Hence option A, B and C are correct.

Additional information: Lyophobic colloids are also known as extrinsic colloids and are very difficult to prepare. Certain special methods are used to prepare them. In lyophobic sols, surface tension and viscosity are the same as that of the medium. Particles of lyophobic colloids can be detected by using ultra microscopes.

Note: Lyophobic colloids are unstable and irreversible i.e. once if the dispersion medium is evaporated and if new solvent is added the same sol cannot be obtained again.