Why does a colloid preferentially adsorb common ion?

Answer 1

A colloid espicially lyophobic sols are weak electrolytes hence they under go partiall ionisation in aqueous medium and they attain equillibrium between dissociated and the undissociated part but the equillibrium is towards the undissociated part because the solution contains some of the true electrolytes which are having low ionization potential hence they undergo complete ionization so due to their presence the colloid can't completely dissociate.but when a excess of common ion is added to maintain the constant equillibrium value the number of free ions(which are in common with the lattice of colloid)should be reduced as

their is on avaibility of the ion with opposite charge(because the colloid partially dissociates giving very less number of free ions) wtih out any option the ion adsorbs on the surface of the colloid

Answer 2

A colloid preferentially adsorbs a common ion because of the electrostatic attraction between the charged particles in the colloid and the common ion in the surrounding solution. The common ion can effectively neutralize the charge on the colloidal particles, leading to a decrease in the electrostatic repulsion between the particles and allowing them to come closer together and form aggregates. This process is known as coagulation or flocculation.