Question

Why is ferric hydroxide colloid positively charged when prepared by adding ferric chloride to hot water?

• A. Due to precipitation of ferric hydroxide there is an excess of $Fe^{3+}$ ions.
• B. Due to preferential adsorption of $Fe^{3+}$ ions by the sol of $Fe(OH)_3$.
• C. Due to absence of any negatively charged ion.
• D. Due to adsorption of $OH^-$ and $Cl^-$ ions, the remaining sol has only $Fe^{3+}$ ions.

Answer 1

Answer: (B)

Due to preferential adsorption of $Fe^{3+}$ ions by the sol of $Fe(OH)_3$.

Answer 2

The adsorption of positively charged $Fe^{3+}$ ions by the sol of hydrated ferric oxide results in positively charged colloid.