The newest 20 of 47 written questions. Open one to see it on the real paper.
Explain why compounds containing Co 2+ ions are coloured.
See it on the paper →A few drops of water are added to a piece of dry cobalt( II ) chloride paper. Describe the colour change that is seen. Write an equation for the reaction that causes this colour change. colour change: from to equation
See it on the paper →Explain why a solution containing complex ion A and a solution containing complex ion B are different colours.
See it on the paper →An excess of NH 3 (aq) is added to CuSO 4 (aq). Describe any further observations made. (c) (i)
See it on the paper →Write an equation for the reaction taking place.
See it on the paper →Complete Fig. 3.1 to show the splitting of the d-orbitals in a tetrahedral complex. (iii) energy
See it on the paper →Co 2+ ions form a different complex ion, M. Each M ion contains two Co 2+ ions, both of which are octahedrally coordinated, but the ligands are different from the ligands in G. Explain why G and M have different colours.
See it on the paper →State the colour change seen in this precipitation reaction. from to
See it on the paper →Complete the ionic equation for this precipitation reaction. 2+
See it on the paper →Give the formula of E.
See it on the paper →The d-orbitals of the cobalt atom or ion present in E are split in energy. State the number of d-orbitals that are at a higher energy level and the number of d-orbitals that are at a lower energy level. number of d-orbitals at a higher energy level number of d-orbitals at a lower energy level (iii)
See it on the paper →Define the term non-degenerate d-orbitals.
See it on the paper →Co 2+ ions form a different complex ion, M. Each M ion contains two Co 2+ ions, both of which are octahedrally coordinated, but the ligands are different from the ligands in G. Explain why G and M have different colours.
See it on the paper →Potassium iron( III ) ethanedioate, K 3 [Fe(C 2 O 4 ) 3 ], dissolves in water to form a green solution. Explain why transition elements can form coloured complexes.
See it on the paper →Solutions containing the [Ag(NH 3 ) 2 ] + complex are colourless. Explain why this complex is colourless.
See it on the paper →Explain why iron complexes are coloured.
See it on the paper →Aqueous solutions of complexes [Fe(H 2 O) 6 ] 3+ and [Fe(H 2 O) 5 SCN] 2+ are different colours. Explain why these complexes are different colours.
See it on the paper →Describe the colour change seen in reaction 3. original colour of [Co(H 2 O) 6 ] 2+ (aq) final colour after addition of an excess of conc. HCl (aq)
See it on the paper →Suggest why a solution of Cu 2+ is coloured but solid CuI is white.
See it on the paper →A solution of [Cu(EDTA)] 2– ions is pale blue while a solution of [Cu(NH 3 ) 4 (H 2 O) 2 ] 2+ ions is deep blue. Explain this difference in colour.
See it on the paper →Most candidates correctly drew three higher and two lower energy levels for the splitting of the d-orbitals in a tetrahedral complex.
— Examiner report, February/March 2025, 9701/42 Q3(a)(iii) (Cambridge)
This question proved difficult for some candidates. Many did not reference that Cu2+ is d9 / had partially filled d subshell and Cu+ is d10 / full d subshell.
— Examiner report, October/November 2023, 9701/41 Q5(d)(iv) (Cambridge)
This discriminated well. Candidates who realised they were being asked to explain the colour difference between two complexes often scored two marks.
— Examiner report, October/November 2023, 9701/42 Q4(f) (Cambridge)
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