Lesson 3.2.5.2

3.2.5.2 Substitution reactions Quiz: AQA Chemistry, Unit 2

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.2.5.2, Substitution reactions: 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. Which of these is a monodentate ligand?

    • Water, H2O
    • H2NCH2CH2NH2
    • Ethanedioate ion, C2O4^2-
    • EDTA4-

  2. Which ligand is multidentate?

    • EDTA4-
    • Water, H2O
    • Chloride ion, Cl-
    • Ammonia, NH3

  3. What is the denticity of the ethanedioate ion, C2O4^2-?

    • Monodentate
    • Tridentate
    • Bidentate
    • Hexadentate

  4. Which pair of ligands is similar in size and uncharged?

    • CN- and Cl-
    • NH3 and H2O
    • Cl- and H2O
    • Cl- and NH3

  5. Which metal ion shows exchange of NH3 and H2O without a change in co-ordination number?

    • Co2+ and Cu2+
    • Cu+ only
    • Fe3+ only
    • Ag+ only

  6. Why can exchange of H2O by Cl- change the co-ordination number of a metal ion?

    • Cl- is larger than H2O, so fewer ligands can fit around the metal ion
    • Cl- is uncharged, so it cannot bond to metal ions
    • H2O is multidentate and Cl- is monodentate only
    • Cl- is smaller than H2O, so more ligands can fit around the metal ion

  7. What is the chelate effect?

    • Metal ions reacting with chloride to form a solid precipitate
    • Monodentate ligands replacing bidentate ligands in a complex
    • Oxidation of a metal ion by a ligand
    • Bidentate and multidentate ligands replacing monodentate ligands in a complex

  8. Which complex is an iron(II) complex with a multidentate ligand, and what does it transport?

    • Chlorophyll, which transports water
    • Haemoglobin, which transports carbon dioxide
    • Haem, which transports oxygen in blood
    • Vitamin B12, which transports sodium ions

  9. Why is carbon monoxide toxic?

    • It replaces oxygen co-ordinately bonded to Fe(II) in haemoglobin
    • It oxidises Fe(II) to Fe(III) in haemoglobin
    • It dissolves haemoglobin in the blood plasma
    • It reacts with the ligands to form solid precipitates

  10. Which equation shows the formation of an incompletely substituted complex?

    • [Cu(H2O)6]2+ + 6NH3 -> [Cu(NH3)6]2+ + 6H2O
    • [Cu(H2O)6]2+ + 2NH3 -> [Cu(NH3)2(H2O)4]2+ + 2H2O
    • [Cu(H2O)6]2+ + 4Cl- -> [CuCl4]2- + 6H2O
    • Cu2+ + 2e- -> Cu

  11. In the reaction [Cu(H2O)6]2+ + 4Cl- -> [CuCl4]2- + 6H2O, how does the co-ordination number of copper change?

    • It changes from 2 to 4
    • It stays at 6
    • It changes from 6 to 4
    • It changes from 4 to 6

  12. What is the balanced equation for ethanedioate ions displacing water from [Cu(H2O)6]2+? (The ethanedioate is C2O4^2-.)

    • [Cu(H2O)6]2+ + C2O4^2- -> Cu(C2O4) + 6H2O
    • [Cu(H2O)6]2+ + 2C2O4^2- -> [Cu(C2O4)2] + 6H2O
    • [Cu(H2O)6]2+ + C2O4^2- -> [Cu(C2O4)(H2O)4] + 2H2O
    • [Cu(H2O)6]2+ + C2O4^2- -> [Cu(C2O4)2]2+ + 6H2O

  13. Why is the chelate effect favourable in terms of entropy?

    • Polydentate ligands lower the total number of particles in solution
    • Polydentate ligands make the reaction endothermic and disorder falls
    • Entropy is always unchanged in ligand exchange reactions
    • Replacing monodentate ligands with a polydentate ligand releases more particles, increasing disorder

  14. Which property of EDTA4- makes it useful for removing metal ions from solution?

    • It is a monatomic ion that precipitates metals
    • It is a neutral molecule with no lone pairs
    • It is monodentate and forms weak bonds with all metals
    • It is multidentate and forms very stable complexes with metal ions

  15. Explain in terms of enthalpy and entropy why a chelate complex is more stable than a complex with monodentate ligands.

    • The enthalpy change is similar, but the entropy increase from more particles produced makes the overall free energy change more favourable
    • The entropy decreases because the complex is more ordered
    • The reaction is endothermic and so stability increases with temperature
    • The enthalpy change is larger and positive, so the complex is more stable

  16. A student adds concentrated HCl to [Cu(H2O)6]2+ and the solution turns from blue to yellow-green. Which best explains this?

    • Cu2+ is reduced to Cu+ metal by the chloride ions
    • A precipitate of copper chloride forms and colours the solution
    • H2O is oxidised to oxygen gas by the chloride ions
    • Cl- ligands replace H2O ligands and change the co-ordination number and colour

  17. Which statement about the iron(II) complex in haemoglobin is correct?

    • Iron is oxidised to iron(III) when oxygen binds
    • Oxygen replaces the iron ion in the complex
    • Oxygen forms an ionic bond with iron(II)
    • Oxygen forms a co-ordinate bond to the iron(II) centre

  18. A complex with four monodentate ligands and one bidentate ligand has what co-ordination number?

    • 8
    • 6
    • 5
    • 4

  19. Which species is the best example of a complex that has a chelate effect when formed?

    • [Cu(H2O)6]2+ alone with six water ligands
    • [Cu(en)2(H2O)2]2+ with two bidentate ethylenediamine ligands
    • [CuCl4]2- with four monodentate chloride ligands
    • [Cu(NH3)4(H2O)2]2+ with monodentate ligands

  20. Why is ammonia, NH3, a monodentate ligand?

    • It has one lone pair that it can donate to a metal ion
    • It has three lone pairs that all bond to one metal
    • It has no lone pairs of electrons
    • It has two lone pairs on separate nitrogen atoms

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