Predict which of the following will be coloured in aqueous solution and why?
\(Sc^{3+}, Fe^{3+}, Zn^{2+}\)
[Atomic numbers: Sc = 21, Fe = 26, Zn = 30]
\(Sc^{3+}, Fe^{3+}, Zn^{2+}\)
[Atomic numbers: Sc = 21, Fe = 26, Zn = 30]
Solution and Explanation
Among the given ions, Fe3+ is coloured in aqueous solution because it has unpaired electrons in its d-orbital, which allows d-d transitions.
On the other hand:
- Sc3+ has an empty d-orbital (d0 configuration), so no d-d transition occurs → Colourless.
- Zn2+ has a fully filled d-orbital (d10 configuration), so no d-d transition occurs → Colourless.
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