Question

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

• A. $KCl$
• B. $KN{O}_3$
• C. $K_{2}S{O}_4$
• D. $K_3\left[Fe{\left(CN\right)}_6\right]$

Answer 1

Answer: (D)

$K_3\left[Fe{\left(CN\right)}_6\right]$

The colloidal particles in ferric hydroxide carry a positive charge and hence ferric hydroxide sol is positively charged.

Applying Hardy Schulze rule:
The active ion for the coagulation of the ferric hydroxide solution must be negatively charged and highest the negative charge of the active ion, most effective coagulating active ion.

Here, $K_3\left[Fe\right(CN{)}_6]\to 3K^{+}+[Fe(CN{)}_6{]}^{3-}$ and this coordination species has highest negative charge.

Hence, option D is the most effective coagulating active ion.