Question

Explain what is observed when an electrolyte (AlCl₃) is added to a colloidal solution of arsenious sulphide (As₂S₃).

Answer 1

When AlCl₃ is added to a colloidal solution of arsenious sulphide (As₂S₃), the Al³⁺ ions neutralize the negative charge on the colloidal particles. This causes the particles to lose repulsion, come closer, and coagulate, resulting in precipitation of the solution. This follows the Hardy-Schulze rule, where Al³⁺ has a high coagulating power for negatively charged As₂S₃ solution. Thus, AlCl₃ induces rapid coagulation of arsenious sulphide sol.