Which one of the following is most effective in causing the coagulation of an $\mathrm{As}_2 \mathrm{~S}_3$…
Which one of the following is most effective in causing the coagulation of an $\mathrm{As}_2 \mathrm{~S}_3$ sol?
$\mathrm{KCl}$
$\mathrm{AlCl}_3$
$\mathrm{MgSO}_4$
$\mathrm{K}_3 \mathrm{Fe}(\mathrm{CN})_6$
Solution
$\mathrm{As}_2 \mathrm{~S}_3$ is a negative sol. It is obvious that cations are effective in coagulating negative sols. According to Hardy Schulze rule, greater the valency of the coagulating ion, greater is its coagulating power. Thus, out of the given, $\mathrm{AlCl}_3\left(\mathrm{Al}^{3+}\right)$ is most effective for causing coagulation of $\mathrm{As}_2 \mathrm{~S}_3$ sol.