Question

What is the colour of the product when ammonia reacts with a solution of \(Cu^{2+}\)?

• A. Orange
• B. Green
• C. Deep blue
• D. Yellow

Answer 1

The Correct Option is C

When ammonia (\(NH_3\)) is added to a solution containing copper ions (\(Cu^{2+}\)), a complex ion is formed. Initially, ammonia reacts with the \(Cu^{2+}\) ions to produce a pale blue precipitate of copper(II) hydroxide:

\(Cu^{2+} + 2OH^- \rightarrow Cu(OH)_2\)

Upon adding excess ammonia, this precipitate dissolves, forming a deep blue complex ion, [\(Cu(NH_3)_4]^{2+}\):

\(Cu(OH)_2 + 4NH_3 \rightarrow [Cu(NH_3)_4]^{2+} + 2OH^-\)

The formation of this complex ion is responsible for the deep blue color of the final solution. Therefore, the correct answer is: Deep blue.

Answer 2

When ammonia (NH₃) reacts with a solution of copper(II) ions (Cu²⁺), it forms a complex ion, specifically [Cu(NH₃)₄]²⁺, which is characterized by a deep blue color. This deep blue solution is the result of the formation of the copper-ammonia complex, where the ammonia molecules coordinate with the copper ion, altering the electronic structure of the copper ion and leading to the distinct blue color.

The correct answer is Deep blue.