Coloured complexes questions

Assignment: Question Topic 13.2 : Coloured complexes

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Suggest why compounds of copper(l) and compounds of scandium(III) are colourless whilst compounds of copper(II) and iron(III) are coloured.

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The hexahydrated iron(III) ion, [Fe(H2O)6]3+, is yellowish brown in colour.
Explain:

i. why it is coloured.

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ii. why it has a different colour to the iron(III) hexacyanide ion, [Fe(CN)6]3-.

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The thiocyanate ion, SCN− and the hydroxide ion, OH− are both monodentate ligands. The thiocyanate ion is higher in the spectrochemical series than the hydroxide ion.

i.  Explain what is meant by the term monodentate ligand.

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ii. What information about the splitting of the d orbitals can be deduced from the fact that the thiocyanate ion is higher in the spectrochemical series than the hydroxide ion?

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Consider the following absorption spectra of two different complex ions of copper(II).

i.  Using the colour wheel in Section 17 of the IB data booklet deduce what colour is absorbed by (a) [Cu(H2O)6]2+ and (b) [Cu(NH3)4(H2O)2]2+.

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ii. Using the colour wheel in Section 17 of the IB data booklet deduce what colour is transmitted by (a) [Cu(H2O)6]2+ and (b) [Cu(NH3)4(H2O)2]2+.

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iii. Use the absorption spectra to deduce which is higher in the spectrochemical series, NH3 or H2O.

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iv. Explain why [Fe(H2O)6]2+ has a different colour to [Cu(H2O)6]2+.

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