Question

The metal hydroxide which is soluble in excess of ammonium hydroxide is:
A.$Fe{(OH)_2}$
B.$Fe{(OH)_3}$
C.$Cu{(OH)_2}$
D.$Al{(OH)_3}$

Answer 1

Hint: We have to remember that the ammonium hydroxide is a volatile colorless solution with a pungent odor. It is also called ammonia in water. Ammonia water generally will dissolve Group 1 that is alkali metals of the modern periodic table and other electropositive metals.

Complete step by step answer:
We know that iron exists in an oxidation state of $ + 2{\text{ and }} + 3$. And it is a moderately active metal and an inorganic substance. Hence it is not soluble in excess ammonium hydroxide. Because ammonium hydroxide holds the property of dissolving only organic compounds.
So, the option A and option B is not the correct answer.
Also, iron reacts with ammonium hydroxide to form a complex which is precipitated and then it further reacts with water to form iron hydroxide. It is insoluble in ammonium water.
Let, us look as option C - $Cu{(OH)_2}$
Copper (II) hydroxide reacts with a solution of excess ammonia to form a deep blue solution of tetraamine copper complex ions. In the presence of oxygen it acts as a catalyst for oxidation of ammonia. It results in forming copper ammine nitrites.
The reaction can be given as,
$Cu{(OH)_2} + 4N{H_4}OH \to [Cu{(N{H_3})_4}]{(OH)_2} + 4{H_2}O \to Cu{(N{O_2})_2}(N{H_3})$

Copper (II) hydroxide is amphoteric in nature and soluble in excess ammonium hydroxide.
Hence, option C. is the correct answer.
Let us take a look at option D.
Just like copper hydroxide, aluminium hydroxide is also insoluble in excess ammonium hydroxide. It forms a precipitate which is insoluble.

 Hence option C is the correct answer.

Note: We have to know that the ammonium hydroxide is a strong solvent. It generally dissolves organic compounds only. This is the main reason why copper hydroxide and aluminium hydroxide is insoluble in ammonium hydroxide. As they are inorganic compounds. Ammonium hydroxide is a colorless substance with a highly volatile nature and pungent odor. Dilute solution of ammonia in water is used as a common household cleaning agent. It is also used in various pharmaceutical processes as an alkalizer.