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Question: Answered & Verified by Expert
Wavelength of red light is absorbed by the complex
ChemistryCoordination CompoundsAIIMSAIIMS 2007
Options:
  • A \(\left[\mathrm{Cu}(\mathrm{CN})_4\right]^{2-}\)
  • B \(\left[\mathrm{Cu}\left(\mathrm{NH}_3\right)_4\right]^{2+}\)
  • C \(\mathrm{CuSO}_4\)
  • D \(\mathrm{Cu}(\mathrm{CN})_2\).
Solution:
1904 Upvotes Verified Answer
The correct answer is: \(\left[\mathrm{Cu}\left(\mathrm{NH}_3\right)_4\right]^{2+}\)
When \(\mathrm{NH}_4 \mathrm{OH}\) is added to the solution containing \(\mathrm{Cu}^{2+}\) ions, deep blue solution is obtained.
\(\mathrm{Cu}^{2+}+4 \mathrm{NH}_4 \mathrm{OH} \rightarrow\underset{\text{deep blue solution}}{\left[\mathrm{Cu}\left(\mathrm{NH}_3\right)_4\right]^{2+}}+4 \mathrm{H}_2 \mathrm{O}\)
Hydrated cupric compounds absorb radiations corresponding to red light and the transmitted colour is greenish blue (which is complementary to red colour). Thus, cupric compounds give greenish-blue colour.

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