Question

The best coagulant for the precipitation of $Fe(OH{)}_3$ sol is:

• A. $N{a}_{2}HP{O}_3$
• B. $NaN{O}_3$
• C. $N{a}_{3}P{O}_4$
• D. $N{a}_{2}S{O}_4$

Answer 1

The correct option is C $N{a}_{3}P{O}_4$

According to Hardy Schulze, greater is the valency of oppositely charged ion of the electrolyte being added, easier is the coagulation.
Here, $P{O}_4^{3-}$ is most effective for positively charged $Fe(OH{)}_3$ sol as it has the highest negative charge.