Question

Why some metallic hydroxides are soluble in excess of ammonium hydroxide? Explain with a reaction involved.

Answer 1

Some metallic hydroxides are soluble in excess ammonium hydroxide because they react with ammonium hydroxide to form soluble complex ions.

Example: Zinc hydroxide dissolves in excess ammonium hydroxide to form a soluble complex.

\[\ce{Zn(OH)2 ​+ 4NH4​OH → [Zn(NH3​)4​](OH)2​ + 4H2​O}\]

Thus, Zn(OH)₂ dissolves in excess NH₄OH due to the formation of a soluble complex.