Question

On adding excess of ammonium hydroxide to a copper sulphate solution:
(a) a deep blue solution is obtained
(b) no change is observed
(c) blue precipitate of copper hydroxide is obtained
(d) black precipitate of copper hydroxide is obtained

Answer 1

Copper has 2 oxidation states, +2 and +1 state. Copper(II) is usually seen as a blue hydrate ion ${{[Cu({{H}_{2}}S{{O}_{4}})]}^{2+}}$.

Complete step by step solution :
In Copper sulphate, the oxidation state of copper is +2. Copper sulphate can react with ammonium hydroxide in stoichiometric amounts to form a blue precipitate of copper hydroxide. The reaction is given as
$CuS{{O}_{4}}+2N{{H}_{4}}OH\to Cu{{(OH)}_{2}}+{{(N{{H}_{4}})}_{2}}S{{O}_{4}}+4{{H}_{2}}O$
When excess of ammonium hydroxide is added, the copper hydroxide formed will react with ammonium sulphate solution and ammonium hydroxide to form a complex compound. That is, the blue precipitate of copper hydroxide dissolves to form a deep blue solution of the complex. The reaction is given as
$\underset{{}}{\mathop{Cu{{(OH)}_{2}}}}\,+{{(N{{H}_{4}})}_{2}}S{{O}_{4}}+2N{{H}_{4}}OH\to [Cu{{(N{{H}_{3}})}_{4}}]S{{O}_{4}}+{{H}_{2}}O$
The product formed is a complex named tetrammine copper(II) sulphate.

Therefore, the correct answer to the question is option (a).

Additional Information: Copper is a metal with a melting point of ${{1083}^{o}}C$ and a boiling point of${{2582}^{o}}C$. Density of copper is$8.92g/c{{m}^{3}}$. It is a reddish yellow metal which is usually inactive. But it dissolves readily in $HN{{O}_{3}}$ and in hot ${{H}_{2}}S{{O}_{4}}$. It is a transition metal belonging to d-block. Therefore, due to the presence of d-orbital it has the ability to form wide varieties of complexes. Copper has a very low chemical reactivity. Copper has a wide range of applications, such as in industries, biomedical, agriculture, etc. Copper is released into the environment by both natural sources and human activities.
Note : When excess ammonia solution or ammonium hydroxide solution is added, the blue precipitate of copper hydroxide dissolves and a complex of copper is formed which is deep blue solution. Not a precipitate.