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Coordination number and colour changes: Edexcel International A Level Chemistry questions

Edexcel International A Level Chemistry past-paper questions on 17.1.4 Coordination number and colour changes, 2019–2025, with mark schemes and examiner’s reports where available.

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  1. Q21(a)(ii)

    January 2025 · Unit 5

    3 marks17.1.1 Transition metals: electron configurations and oxidation numbers17.1.4 Coordination number and colour changes
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    The start of question 21

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  2. Q18(a)(ii)

    October 2024 · Unit 5

    2 marks17.1.4 Coordination number and colour changes
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    The start of question 18

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  3. Q16(b)(i)

    June 2024 · Unit 5

    3 marks17.1.6 Bidentate and hexadentate ligands, and haemoglobin17.1.4 Coordination number and colour changes
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    The start of question 16

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  4. Q17(a)(i)

    January 2024 · Unit 5

    3 marks17.1.3 Why complex ions are coloured17.1.4 Coordination number and colour changes
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    The start of question 17

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  5. Q3

    October 2023 · Unit 5

    1 mark17.1.4 Coordination number and colour changes17.1.6 Bidentate and hexadentate ligands, and haemoglobin
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  6. Q7

    June 2023 · Unit 5

    1 mark17.1.4 Coordination number and colour changes
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  7. Q2(a)

    January 2023 · Unit 5

    1 mark17.1.4 Coordination number and colour changes17.1.6 Bidentate and hexadentate ligands, and haemoglobin
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    The start of question 2

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  8. Q22(b)(iii)

    October 2022 · Unit 5

    2 marks17.1.4 Coordination number and colour changes17.1.5 Shapes of complexes, including cis-platin
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    The start of question 22

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  9. Q6

    June 2021 · Unit 5

    1 mark17.1.6 Bidentate and hexadentate ligands, and haemoglobin17.1.4 Coordination number and colour changes
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  10. Q21(f)

    June 2021 · Unit 5

    1 mark17.1.5 Shapes of complexes, including cis-platin17.1.4 Coordination number and colour changes
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    The start of question 21

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  11. Q8

    January 2021 · Unit 5

    1 mark17.1.4 Coordination number and colour changes17.2.4 Ligand exchange and the stability of complexes
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  12. Q19(b)(iii)

    January 2021 · Unit 5

    2 marks17.1.4 Coordination number and colour changes
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    The start of question 19

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  13. Q2(d)

    January 2021 · Unit 6

    1 mark17.1.4 Coordination number and colour changes8.A.2 Oxidation, reduction, oxidising and reducing agents
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    The start of question 2

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  14. Q18

    October 2020 · Unit 5

    1 mark17.1.6 Bidentate and hexadentate ligands, and haemoglobin17.1.4 Coordination number and colour changes
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  15. Q25(c)(ii)

    October 2020 · Unit 5

    1 mark17.1.5 Shapes of complexes, including cis-platin17.1.4 Coordination number and colour changes
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    The start of question 25

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All 15 questions on Coordination number and colour changes, as a list
  1. January 2025, Unit 5, Q21(a)(ii) (3 marks): An aqueous solution of iron(II) sulfate is pale green in colour. When left exposed to the air the solution turns brown. Explain why this colour change occurs. I
  2. October 2024, Unit 5, Q18(a)(ii) (2 marks): Explain why the two iron complex ions are different colours. (2)
  3. June 2024, Unit 5, Q16(b)(i) (3 marks): Complete the table for the complex. (3) Charge on nickel ion Type of ligand Co‑ordination number of the nickel ion Shape of metal complex around the nickel ion
  4. January 2024, Unit 5, Q17(a)(i) (3 marks): Explain why the three isomers have different colours. (3)
  5. October 2023, Unit 5, Q3 (1 mark): What is the co-ordination number of chromium in the complex ion shown? + Cl H2N NH2 H2C CH2 Cr H2C CH2 H2N NH2 Cl A 2 B 3 C 4 D 6
  6. June 2023, Unit 5, Q7 (1 mark): The structure of the complex Cr2(CH3CO2)4(H2O)2 is shown. CH3 C CH3 O O C O O H2O Cr Cr OH2 O O C O O CH3 C CH3 What is the coordination number of chromium in t
  7. January 2023, Unit 5, Q2(a) (1 mark): What is the coordination number of chromium(III) in this complex ion? (1) A 2 B 3 C 4 D 6
  8. October 2022, Unit 5, Q22(b)(iii) (2 marks): Explain why the shape of the complex ion changes when concentrated hydrochloric acid is added. (2)
  9. June 2021, Unit 5, Q6 (1 mark): Copper(II) ions form a complex with 1,2-diaminoethane (symbol ‘en’) with the formula Cu(en)3 2+. What type of ligand is 1,2-diaminoethane, and what is the coord
  10. June 2021, Unit 5, Q21(f) (1 mark): Give a possible reason why the chloro complexes of iron ions have a coordination number of four rather than six. (1)
  11. January 2021, Unit 5, Q8 (1 mark): Cobalt chloride is used as a test for the presence of water. This test depends on the fact that A anhydrous cobalt(II) chloride is blue and hydrated cobalt(II)
  12. January 2021, Unit 5, Q19(b)(iii) (2 marks): Suggest an explanation for the change of V into T on shaking. (2)
  13. January 2021, Unit 6, Q2(d) (1 mark): Give the colour change observed in Step 1. (1)
  14. October 2020, Unit 5, Q18 (1 mark): What is the coordination number of the nickel(II) ion and the overall charge, m, of this complex? m Cl O O C O O C Ni C O O C O O Cl Coordination number of Over
  15. October 2020, Unit 5, Q25(c)(ii) (1 mark): The Lanthanides The lanthanides form a series in the Periodic Table comprising the elements from lanthanum, La (Z = 57) to lutetium, Lu (Z = 71). They have impo

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