when 2 or more ions are present in the despersion medium then ion common to the colloidal particle is adsorbed.
for eg when ferric hydroxide sol is prepared by the hydrolysis of ferric chloride has a positive charge becoz of the preferential adsorption of Fe 3+on the surface of the ferric hydroxide particle.
Fe(OH)3 + Fe3+ ---------------->Fe(OH)3.Fe3+
Moderation Team
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