Lesson 3.2.5.4

3.2.5.4 Formation of coloured ions Quiz: AQA Chemistry, Unit 2

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.2.5.4, Formation of coloured ions: 20 multiple choice questions for the AQA Chemistry (7405), Unit 2: Inorganic chemistry, written with Revision Ninja.

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The 20 questions

  1. Why are transition metal compounds coloured?

    • Some wavelengths of visible light are absorbed and the remaining wavelengths are transmitted or reflected
    • They emit light when heated only
    • All wavelengths of visible light are absorbed
    • They reflect ultraviolet light only

  2. What happens to d electrons when light is absorbed by a transition metal ion?

    • They move from the excited state to a higher shell
    • They are removed from the ion completely
    • They are converted to neutrons
    • They move from the ground state to an excited state

  3. Which equation gives the energy difference between the ground and excited d electron states?

    • delta E = nRT
    • delta E = kT
    • delta E = mc^2
    • delta E = h x nu = hc/lambda

  4. Which factor does NOT directly change the energy gap delta E in a transition metal complex?

    • The colour of the sample container
    • The oxidation state of the metal
    • The co-ordination number
    • The identity of the ligand

  5. What is the wavelength of light absorbed when delta E = 3.98 x 10^-19 J? (h = 6.63 x 10^-34 J s, c = 3.00 x 10^8 m s-1)

    • 600 nm
    • 700 nm
    • 500 nm
    • 400 nm

  6. A solution absorbs mainly red light. What colour does it appear?

    • Yellow
    • Red
    • Blue-green
    • Black

  7. What is a simple colorimeter used for in transition metal chemistry?

    • Measuring the melting point of a solid
    • Counting the number of ligands around a metal
    • Determining the concentration of coloured ions in solution
    • Measuring the pH of a solution directly

  8. What does a colorimeter calibration graph plot?

    • Temperature against time
    • Absorbance against concentration of the coloured solution
    • Concentration against pH
    • Mass against volume

  9. Why does the colour of [Cu(H2O)6]2+ change when it reacts with ammonia to form [Cu(NH3)4(H2O)2]2+?

    • Ammonia removes the d electrons from copper
    • A gas is evolved that changes the light transmitted
    • The copper ion is reduced to copper metal
    • The change of ligand alters the energy gap delta E between d levels, so a different wavelength is absorbed

  10. Why is the colour of [Cu(H2O)6]2+ different from that of [CuCl4]2-?

    • The copper ion has different electrons in each complex
    • The different ligands change delta E, so different wavelengths of visible light are absorbed
    • The water ligands are coloured but the chloride ligands are not
    • The chloride ions are colourless so they remove all colour

  11. A solution has an absorbance reading that is directly proportional to concentration. Which law is being obeyed?

    • Charles's law
    • Hess's law
    • Boyle's law
    • Beer-Lambert law

  12. Why is Zn2+(aq) colourless when Cu2+(aq) is coloured?

    • Zn2+ does not form any aqueous complexes
    • Zn2+ absorbs all visible wavelengths
    • Zn2+ is a gas in aqueous solution
    • Zn2+ has a full 3d10 sub-level, so no d-d transition in visible light occurs

  13. What is the energy gap delta E for absorption of light with wavelength 600 nm? (h = 6.63 x 10^-34 J s, c = 3.00 x 10^8 m s-1)

    • 9.9 x 10^-19 J
    • 3.3 x 10^-19 J
    • 6.6 x 10^-19 J
    • 1.1 x 10^-19 J

  14. A change in co-ordination number alters the colour of a complex because it changes what?

    • The mass of the metal ion
    • The number of protons in the nucleus
    • The energy gap delta E between the d-electron levels
    • The number of electrons in the outer s sub-level only

  15. Explain why a colorimeter needs a calibration graph before measuring an unknown copper(II) solution.

    • The calibration graph converts colour into a temperature
    • The absorbance must be compared with standard solutions of known concentration to find an unknown concentration
    • The colorimeter cannot measure absorbance without knowing the pH
    • The calibration graph gives the mass of copper directly

  16. Which statement explains why the colour of a transition metal complex depends on its ligand?

    • Ligands add extra electrons that absorb all light
    • Ligands change the splitting of d orbitals, which alters the energy of light absorbed
    • Ligands remove the d electrons completely from the metal
    • Ligands are always colourless so they do not affect the colour

  17. Which transition metal ion gives a blue colour in aqueous solution?

    • Na+
    • Zn2+
    • Ca2+
    • Cu2+

  18. Which statement about the absorption of visible light is correct?

    • Visible light is never absorbed by transition metal ions
    • Absorption only occurs at wavelengths shorter than ultraviolet
    • Absorption makes all solutions colourless
    • Absorption of visible light is used in spectroscopy to identify and measure substances

  19. Explain why the absorption of light in a transition metal complex is linked to d electrons.

    • The d electrons emit light in the visible region as they fall
    • d electrons only absorb ultraviolet radiation
    • Absorbed photons supply exactly the energy gap between two d-electron levels, promoting an electron
    • Absorbed photons remove d electrons from the metal

  20. What is the approximate wavelength in nm for light of energy 2.0 x 10^-19 J? (h = 6.63 x 10^-34 J s, c = 3.00 x 10^8 m s-1)

    • 1000 nm
    • 100 nm
    • 3000 nm
    • 500 nm

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