Question

How is the following sol (in water) prepared?

Ferric hydroxide

Answer 1

Ferric hydroxide sol (colloidal ferric hydroxide) is prepared by the hydrolysis of ferric chloride solution in warm water. When an aqueous solution of ferric chloride is boiled with water, it undergoes hydrolysis to form a reddish brown colloidal solution of ferric hydroxide and hydrochloric acid. The chemical reaction is:

\[\ce{FeCl3 + 3H2O ->[boil] Fe(OH)3 (colloidal ferric hydroxide) + 3HCl}\]

This freshly precipitated ferric hydroxide forms a sol due to the peptization by the (Fe³⁺) ions adsorbing on the colloidal particles, giving them positive charge and stabilizing the dispersion in water.