1. Copper Sulfate Solution: Initially, you have a solution of copper sulfate, which is often blue in color. The copper ions (\(Cu^{2+}\)) in this solution are responsible for the blue color. The equation for copper sulfate in solution can be represented as:
\[CuSO_4(aq) \rightleftharpoons Cu^{2+}(aq) + SO_4^{2-}(aq)\]
2. Passing Ammonia Gas: When you pass ammonia gas (\(NH_3\)) through this solution, it starts to react with the copper ions. Ammonia gas acts as a Lewis base, meaning it can donate a pair of electrons to form coordinate bonds with metal ions. The reaction with copper ions can be represented as:
\[Cu^{2+}(aq) + 4NH_3(aq) \rightleftharpoons [Cu(NH_3)_4]^{2+}(aq)\]
In this reaction, four ammonia molecules coordinate around each copper ion to form a complex ion called the tetraammine copper(II) ion, represented as \([Cu(NH_3)_4]^{2+}\).
3. Deep Blue Color Formation: The formation of the \([Cu(NH_3)_4]^{2+}\) complex ion results in a deep blue color in the solution. This color change is due to the absorption of specific wavelengths of light by the complex. The complex absorbs light in the red and yellow regions of the visible spectrum, and it appears blue to our eyes because blue light is not absorbed but rather transmitted or reflected.
So, the deep blue color of the solution is indeed due to the formation of \([Cu(NH_3)_4]^{2+}\) complex ions. Each copper ion in the solution forms this complex with four ammonia molecules, leading to the characteristic color change. This complexation reaction is an example of coordination chemistry, where ligands (\(NH_3\) in this case) coordinate with metal ions to form complex ions with unique properties, including color. |
