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

Upon the addition of ammonia (\(NH_3\)) to a solution containing copper ions (\(Cu^{2+}\)), a complex ion is generated. Initially, ammonia interacts with the \(Cu^{2+}\) ions, yielding a pale blue precipitate of copper(II) hydroxide:

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

When excess ammonia is introduced, 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 deep blue hue of the final solution is attributable to the formation of this complex ion. Consequently, the accurate designation is: Deep blue.