Question

The best coagulant for the precipitation of $Fe ( OH )_{3}$ is

• A. $Na_{2}HPO_{3}$
• B. $NaNO_{3}$
• C. $Na_{3}PO_{4}$
• D. $Na_{2}SO_{4}$

Answer 1

Answer: (C)

$Na_{3}PO_{4}$

Answer 2

$Fe ( OH )_{3}$ is a positive sol hence the best coagulant for the precipitation of $Fe ( OH )_{3}$ is $Na _{3} PO _{4}$. The precipitating effect of an ion on dispersed phase of opposite charge increases with the valence of the ions.