Question

Account for the following:

Ferric hydroxide sol is positively charged.

Answer 1

Ferric hydroxide sol is positively charged because the colloidal particles of Fe(OH)₃ preferentially adsorb Fe³⁺ ions from the solution. These Fe³⁺ ions are common to the lattice of Fe(OH)₃ particles and their adsorption imparts a positive charge to the colloidal particles. This charge prevents aggregation, stabilizing the sol by electrostatic repulsion between similarly charged particles.