CAIE A-Level Chemistry 28.3.4 Ligand Effects on d-Orbital Splitting

Practise explaining how changing a ligand alters ΔE, the light absorbed and the complementary colour observed.

Exam points

state that different ligands produce different energy gaps between the split d orbitals
link a changed ΔE to absorption of visible light with a different frequency or wavelength
identify the observed colour as complementary to the absorbed light rather than the absorbed colour itself

[Maximum number: 1]

Copper is a transition element. It forms a wide variety of compounds.

An aqueous solution of copper(II) sulfate, $\mathrm{CuSO}_{4}$ , contains $\left[\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$ complex ions. If an excess of concentrated hydrochloric acid is added to this solution a ligand exchange reaction occurs and $\left[\mathrm{CuCl}_{4}\right]^{2-}$ complex ions are formed.

Explain why the solutions of the two complex ions in Table 5.1 are different colours.

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28.3.4—Ligand effects on orbital splitting question 1