Question

Which one of the following acts as the best coagulating agent for ferric hydroxide sol?

• A. Magnesium chloride
• B. Hydrochloric acid
• C. Aluminium chloride
• D. Potassium oxalate
• E. Potassion ferricyanide

Answer 1

Answer: (E)

Potassion ferricyanide

Ferric Hydroxide is a positively charged solution. To coagulate we need a negatively charged solution. By Hardy-Schulz rule coagulating power of an electrolyte is directly proportional to the valency if active ions.

Hence order of coagulation power is : $\left[Fe\right(CN{)}_6{]}^{4-}>[Cr{O}_4{]}^{2-}>C{l}^{-}$
Hence option D is correct.