Which of the following is the most effective in causing coagulation of ferric hydroxide solution?

Which of the following is the most effective in causing coagulation of ferric hydroxide solution?
  1. $KCl$
  2. $KNO_3$
  3. $K_2SO_4$
  4. $\mathrm{K}_3\left[\mathrm{Fe}(\mathrm{CN})_6\right]$

Solution

Ferric hydroxide solution, is a negatively charged sol. $\begin{aligned} & \mathrm{KCl} \rightleftarrows \mathrm{K}^{+}+\mathrm{Cl}^{-} \\ & \mathrm{KNO}_3 \rightleftarrows \mathrm{K}^{+}+\mathrm{NO}_3^{-} \\ & \mathrm{K}_2 \mathrm{SO}_4 \rightleftarrows 2 \mathrm{~K}^{+}+\mathrm{NO}_4^{2-} \\ & \mathrm{K}_3\left[\mathrm{Fe}(\mathrm{CN})_6\right] \rightleftarrows 3 \mathrm{~K}^{-}+\left[\mathrm{Fe}(\mathrm{CN})_6\right]^{3-} \end{aligned}$ Hence, $\mathrm{K}_3\left[\mathrm{Fe}(\mathrm{CN})_6\right]$ will be most effective in causing coagulation of ferric hydroxide solution.

Asked in: AP EAMCET 2015

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