The nature of charge on resulting colloidal particles when $\mathrm{FeCl}_{3}$ is added to excess of hot water is:

(C) sometimes positive and sometimes negative

JEE Main · 2021 · 26 Feb 2021 · Shift 2 · Surface Chemistry

The nature of charge on resulting colloidal particles when

FeCl_{3}

is added to excess of hot water is:

Answer: (D)

Ferric chloride added to a large excess of hot water hydrolyses to a sol of ferric hydroxide:

FeC l_{3} + 3 H_{2} O \to Fe (OH)_{3} + 3 HCl

A sol particle adsorbs by preference the ion it has in common with the dispersed phase, and here the solution is rich in

F e^{3 +}

. The adsorbed layer of

F e^{3 +}

gives the ferric hydroxide particles a positive charge.

JEE Main · 2021 · 26 Feb 2021 · Shift 2 · Single correct option