Lesson 15A.3

15A.3 Colour of transition metal ions Quiz: Pearson Edexcel Chemistry, Unit 15

20 questions

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Lesson 15A.3, Colour of transition metal ions: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 15: Transition Metals, written with Revision Ninja.

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The 20 questions

  1. Why are many transition metal ions coloured in solution?

    • Metal ions emit light from electron transitions between 4s and 4p levels
    • Colour arises from the nucleus absorbing visible light
    • Ligands split the d orbital energies
    • Colour arises because the ligands themselves are coloured

  2. Why is the Zn2+ ion colourless in aqueous solution?

    • It is a Group 2 ion, so it forms colourless compounds
    • It has a full 3d10 subshell, so no d-d transitions are possible
    • It has a half-filled d subshell, which absorbs no light
    • It has no electrons at all, so no transitions are possible

  3. Why is the Sc3+ ion colourless in aqueous solution?

    • It has no d electrons, so d-d transitions cannot occur
    • It has a full 3d10 subshell that reflects all visible light
    • It is a Group 3 ion, so it forms only colourless salts
    • It has only one d electron, which absorbs in the ultraviolet

  4. How does a change in oxidation number affect the colour of a transition metal ion?

    • It changes the d electron count and the splitting
    • Only ligands affect colour, not oxidation number
    • Oxidation number has no effect on colour
    • Colour is determined only by the mass of the metal

  5. How does changing the ligand affect the colour of a complex ion?

    • Ligand changes have no effect on colour
    • Only the number of water molecules matters, not the type of ligand
    • Ligands always make complexes colourless
    • It changes the energy gap between the split d orbitals

  6. How does a change in coordination number affect the colour of a complex?

    • Coordination number affects only solubility
    • Coordination number has no effect on colour
    • It changes the geometry and the d orbital splitting
    • Coordination number only changes the charge of the complex

  7. Which factor sets the energy of light absorbed in a d-d transition?

    • The number of protons in the nucleus only
    • The mass of the complex only
    • The temperature of the solution only
    • The size of the d orbital splitting

  8. Which aqueous ion is pale green?

    • Zn2+(aq)
    • Mn2+(aq)
    • Cu2+(aq)
    • Fe2+(aq)

  9. What colour is aqueous copper(II) ion, [Cu(H2O)6]2+?

    • Blue
    • Colourless
    • Green
    • Yellow

  10. What colour is aqueous chromium(III) ion?

    • Violet
    • Colourless
    • Orange
    • Yellow

  11. What colour is the aqueous vanadium(II) ion, V2+?

    • Violet
    • Yellow (V5+)
    • Blue (V4+)
    • Green (V3+)

  12. What colour is aqueous cobalt(II) ion?

    • Colourless
    • Pink
    • Yellow
    • Blue

  13. What colour is the complex [Cu(NH3)4(H2O)2]2+ formed from aqueous copper(II) by adding excess ammonia?

    • Yellow
    • Deep blue
    • Pale green
    • Colourless

  14. Why is Ti4+ in TiO2 colourless?

    • It has a full 3d10 subshell, so it reflects all light
    • It is white because of the oxide anion, not the titanium ion
    • It absorbs only ultraviolet light because of its 4s electrons
    • It has no d electrons, so d-d transitions cannot occur

  15. Which species is colourless: [Zn(NH3)4]2+ or [Cu(NH3)4(H2O)2]2+?

    • [Zn(NH3)4]2+, because zinc has a full 3d10 subshell
    • Neither is coloured because both contain a d-block metal
    • [Cu(NH3)4(H2O)2]2+, because copper is a transition metal
    • Both are coloured because both contain ammonia

  16. A student says all transition metal ions are coloured. Which evaluation is best?

    • False, because colour depends only on temperature and the pressure of the solution at 298 K
    • True, because ligands always add colour to the metal ion, so every complex is coloured in solution
    • True, because all d-block elements have partially filled d orbitals and so absorb visible light
    • False, because ions such as Sc3+ and Zn2+ with empty or full d subshells are colourless

  17. Why does exchanging H2O for Cl- change the colour of cobalt(II) from pink to blue?

    • Cobalt is oxidised to Co(III) by the chloride ions, so its colour changes to the blue shade
    • Both the ligand and the coordination number change, altering the d orbital splitting and geometry
    • Cl- makes the solution more acidic, which changes the colour only through a change in pH
    • Only the charge changes, and charge alone determines colour through the size of the metal ion

  18. Why is light absorbed in d-d transitions in the visible region for many aqueous complexes?

    • Visible photons have too much energy to promote d electrons
    • The energy gap between the split d orbitals matches the energy of visible photons
    • The d orbitals are not split by ligands, so visible light passes straight through
    • The energy gap is larger than visible photons, so only ultraviolet is absorbed

  19. Why do V2+ (d3) and V3+ (d2) have different colours?

    • They have identical d electron counts, so the difference must come from the anion
    • The difference is only due to the charge, not the electron configuration
    • Different d electron counts give different splitting and transitions
    • V2+ is colourless because it has no d electrons

  20. Why is Cu2+ (d9) coloured while Zn2+ (d10) is colourless?

    • Zn2+ has more d electrons, so it absorbs all light
    • Cu2+ has more protons, which always absorb visible light
    • Both ions are coloured, but Zn2+ is too dilute to see
    • d-d transitions need a gap between partially filled d orbitals

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