Lesson 15B.2

15B.2 Ligand exchange reactions Quiz: Pearson Edexcel Chemistry, Unit 15

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 15B.2, Ligand exchange reactions: 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. What is a ligand exchange reaction?

    • A reaction in which a precipitate forms from a complex ion as the ligands are removed completely
    • A reaction in which the metal ion changes its oxidation state and the ligands remain unchanged
    • A reaction in which one or more ligands in a complex are replaced by different ligands
    • A reaction in which the complex loses all of its ligands and becomes a simple metal ion

  2. Why is a colour change often seen in ligand exchange?

    • Ligand exchange never changes the colour of a complex
    • Ligands always make a complex colourless
    • The metal changes its oxidation state each time
    • The d orbital splitting changes when the ligands change

  3. What precipitate forms when small amounts of NaOH are added to [Cu(H2O)6]2+?

    • Cu(OH)2(H2O)4, a blue precipitate
    • No precipitate, only a colour change
    • A green precipitate of CuOH
    • Copper metal

  4. What complex forms when excess ammonia is added to the copper(II) precipitate?

    • Copper metal, which is deposited as a solid when ammonia reduces the copper in solution
    • [Cu(NH3)4(H2O)2]2+, a deep blue complex
    • [CuCl4]2-, a yellow-green complex formed with concentrated chloride ions
    • CuCO3 precipitate, which forms when carbonate ions react with the copper(II) ions

  5. Which complex forms when copper(II) is treated with concentrated chloride ions?

    • Cu(OH)2(H2O)4
    • Copper metal
    • [CuCl4]2-
    • [Cu(NH3)4(H2O)2]2+

  6. Which complex forms when [Co(H2O)6]2+ reacts with concentrated chloride ions?

    • [CoCl6]4-, which is green
    • [Co(OH)4]2-, which is colourless
    • [CoCl4]2-, which is blue
    • [Co(NH3)6]2+, which is pink

  7. Which description of the hydroxide of an amphoteric metal is correct?

    • It is a carbonate that forms only in acid, and it reacts with excess base to give a gas
    • It is a metal that is oxidised by excess base to a higher oxidation state and then dissolves
    • It is a species formed when the solution becomes acidic, and it dissolves in excess acid
    • It is amphoteric, reacting with excess base to form a soluble complex ion

  8. How many water ligands are replaced by hydroxide when [Cu(H2O)6]2+ forms the precipitate Cu(OH)2(H2O)4?

    • 4
    • 2
    • 6
    • 1

  9. Which statement about Cr3+ with excess NaOH is correct?

    • Cr3+ is reduced to Cr2+ in excess NaOH, which changes the colour of the solution at once
    • The precipitate stays unchanged in excess base, showing only a simple ligand exchange with water
    • Cr(OH)3 dissolves in excess ammonia to form [Cr(NH3)6]3+, showing that it is a simple ligand exchange
    • Cr(OH)3 dissolves in excess NaOH to form the soluble complex [Cr(OH)6]3-, showing amphoteric behaviour

  10. Does the coordination number change when [Cu(H2O)6]2+ becomes [Cu(NH3)4(H2O)2]2+?

    • Yes, it falls to 2, because the copper is reduced and loses two of its ligands
    • Yes, it falls to 4, because the bulky NH3 ligands cannot fit six around the copper
    • No, it stays at 6, because NH3 and H2O are both monodentate
    • Yes, it rises to 8, because each NH3 ligand donates two electron pairs to the copper

  11. Which equation correctly shows the formation of [CuCl4]2- from [Cu(H2O)6]2+?

    • [Cu(H2O)6]2+ + Cl- gives [CuCl]+ + 6H2O
    • [Cu(H2O)6]2+ + 4Cl- gives [CuCl4]2+ + 6H2O
    • [Cu(H2O)6]2+ + 4Cl- gives [CuCl4]2- + 2H2O
    • [Cu(H2O)6]2+ + 4Cl- gives [CuCl4]2- + 6H2O

  12. What is the coordination number of copper in [CuCl4]2-?

    • 8
    • 2
    • 4
    • 6

  13. Which metal ion gives a hydroxide precipitate with NaOH that dissolves in excess?

    • Fe2+
    • Cr3+
    • Cu2+
    • Co2+

  14. Cu(OH)2 precipitate dissolves in excess aqueous ammonia to form which complex?

    • [Cu(OH)4]2-
    • Cu(NH3)2 precipitate
    • [Cu(NH3)4(H2O)2]2+
    • [CuCl4]2-

  15. Which ligand substitution is accompanied by a colour change from pink to blue?

    • [Cr(H2O)6]3+ to [Cr(NH3)6]3+
    • [Co(H2O)6]2+ to [CoCl4]2-
    • [Fe(H2O)6]2+ to [FeCl6]
    • [Cu(H2O)6]2+ to [Cu(NH3)4(H2O)2]2+

  16. Why is the replacement of a monodentate ligand by a bidentate ligand favoured by entropy?

    • One bidentate ligand releases fewer particles than a monodentate one, so dS falls for the system
    • Two monodentate ligands are released for each bidentate ligand bound, giving a large positive dS for the system
    • The entropy change is unaffected by the number of ligands because they have equal mass
    • Entropy is positive only at high temperature, so the effect is small and does not favour the complex

  17. Which equation correctly shows ligand exchange of [Cu(H2O)6]2+ with ammonia to form [Cu(NH3)4(H2O)2]2+?

    • [Cu(H2O)6]2+ + NH3 gives [Cu(NH3)(H2O)5]2+ + H2O
    • [Cu(H2O)6]2+ + 4NH3 gives [Cu(NH3)4(H2O)2]2+ + 2H2O
    • [Cu(H2O)6]2+ + 4NH3 gives [Cu(NH3)4(H2O)2]2+ + 6H2O
    • [Cu(H2O)6]2+ + 4NH3 gives [Cu(NH3)4(H2O)2]2+ + 4H2O

  18. A ligand exchange gives a complex with a different colour from the original. What can be concluded?

    • The metal must have changed oxidation state
    • The metal has been replaced by a different element
    • The d orbital splitting has changed
    • A new element must have formed in the solution

  19. Which statement correctly describes the reaction of Co2+(aq) with concentrated chloride ions?

    • Co2+ forms blue [CoCl4]2- by replacing water ligands with chloride
    • Chloride ions are removed from the complex, leaving a colourless solution
    • Co2+ is oxidised to Co3+ and forms a pink complex
    • The complex becomes colourless because chloride is a poor ligand

  20. In the reaction of copper(II) with ammonia, what is the first product formed before excess ammonia is added?

    • [Cu(NH3)4]2+, which dissolves the precipitate immediately as soon as any ammonia is added
    • Copper metal, which is deposited on the surface of the glass when the ammonia is first added
    • Cu(OH)2(H2O)4, a blue precipitate formed by ligand replacement
    • [CuCl4]2-, which forms at once because the ammonia supplies chloride ions to the solution

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