Chemistry of transition elements

4(a) (element that forms one or more stable) ions with incomplete/ partially filled 3d-orbitals/d-subshell 1 4(b)(i) 1 O AND T h d © UCLES 2021 Page 7 of 13 4(b)(ii) M1: lower energy level (in between axes) 2 OR OR M2: higher energy level (on the axes) OR 4(c)(i) Circles round both N atoms and all four O– 1 4(c)(ii) M1: (d–d) energy gap / ΔE is different 2 M2: different frequency / wavelength (of light) absorbed 4(c)(iii) ligand exchange / substitution / displacement / replacement 1 4(c)(iv) Fe ( edds )–  1   K = stab Fe ( H O ) 3+edds4–  2 6   4(c)(v) [Fe(edta)]– is more stable as it has the higher K 1 stab 4(c)(vi) K (edta) 1.26×1025 1 K = stab = =3.17 × 104 (31658) min 2sf c K (edds) 3.98×1020 stab © UCLES 2021 Page 8 of 13

2(a) M1: (complexes have two sets of) d orbital(s) of different energy / d-d splitting occurs 4 OR d orbital(s) / d (sub)-shell splits OR (inferred from a movement of an electron) from a lower d to higher d orbital M2: electron(s) promoted / excited OR electron(s) moves to higher (d–)orbital OR electron(s) jumps up (to d–orbital) / jumps to higher (d–orbital) M3: wavelength / frequency / light / photon / hν absorbed OR radiation / energy from visible (region) absorbed M4: colour seen is complementary (to colour absorbed) OR wavelength / frequency / colour / light not absorbed is transmitted / reflected / seen © UCLES 2021 Page 6 of 17 2(b)(i) 4 M1: All charges M2: One octahedral with correct 3D M3: All formulae M4: R is cis, S is trans 2(b)(ii) dipoles cancel 1 2(c)(i) M1: (a species) that donates two lone pairs / forms two coordinate bonds / two dative bonds 2 M2: to a metal atom / metal ion © UCLES 2021 Page 7 of 17 2(c)(ii) 1 structure of the picolinate anion ligand 2(c)(iii) (coordination number) six 1 AND (geometry around Cr) octahedral 2(d)(i) (NH ) Cr O +6 1 4 2 2 7 Cr O +3 2 3 2(d)(ii) (NH ) Cr O → N + Cr O + 4H O 1 4 2 2 7 2 2 3 2 Question Answer Marks

4(a)(i) M1: blue solid / blue ppt 3 M2: [Cu(H O) ]2+ + 2OH– → Cu(OH) + 6H O 2 6 2 2 OR [Cu(H O) ]2+ + 2OH– → Cu(OH) (H O) + 2H O 2 6 2 2 4 2 M3: precipitation / acid-base 4(a)(ii) M1: dark blue solution / deep blue solution 3 M2: [Cu(H O) ]2+ + 4NH → [Cu(NH ) (H O) ]2+ + 4H O 2 6 3 3 4 2 2 2 M3: ligand exchange / substitution / displacement / replacement 4(b) M1: 2 X CuSO and Y Cu 4 M2: type of reaction = redox / disproportionation Question Answer Marks

1(a)(i) [1s2] 2s22p63s23p63d3 1 1(a)(ii) (a molecule or ion formed by a central) metal atom/ion surrounded by / bonded to one or more ligands 1 1(b) 5 [Cr(H O) ]3+(aq) formula of chromium species formed type of reaction 2 6 + NaOH(aq) Cr(OH) or Cr(OH) (H O) precipitation 3 3 2 3 + H O (aq) Cr O 2– / CrO 2– redox / oxidation 2 2 2 7 4 + excess NH (aq) Cr(NH ) 3+ ligand substitution 3 3 6 chromium species: one mark for each correct species type of reaction: two correct for one mark and three correct for two marks 1(c) M1: ΔE is different OR energy gap between d-orbitals is different 2 M2: different frequency / wavelength is absorbed OR different energy / light in visible region is absorbed 1(d)(i) ethanoate ions are bidentate whereas as H O are monodentate 1 2 OR ethanoate ions form two dative bonds whereas H O forms one (dative) bond 2 OR ethanoate ions donate two lone pairs whereas H O donates one (lone) pair 2 1(d)(ii) (coordination number) six AND (geometry around Cr) octahedral 1 1(d)(iii) coordinate / (dative) covalent 1 1(e)(i) 4Cr2+ + O + 4H+  4Cr3+ + 2H O OR 2Cr2+ + O + 2H+  2Cr3+ + H O 2 2 2 2 2 2 M1: correct species M2: balancing 1(e)(ii) Eo = 1.23 – (–0.41) = (+)1.64 V OR Eo = 0.68 – (–0.41) = (+)1.09 V 1 cell cell value linked to (e)(i) © UCLES 2021 Page 5 of 16

2(a) M1: (complexes have two sets of) d orbital(s) of different energy / d-d splitting occurs 4 OR d orbital(s) / d (sub)-shell splits OR (inferred from a movement of an electron) from a lower d to higher d orbital M2: electron(s) promoted / excited OR electron(s) moves to higher (d–)orbital OR electron(s) jumps up (to d–orbital) / jumps to higher (d–orbital) M3: wavelength / frequency / light / photon / hν absorbed OR radiation / energy from visible (region) absorbed M4: colour seen is complementary (to colour absorbed) OR wavelength / frequency / colour / light not absorbed is transmitted / reflected / seen © UCLES 2021 Page 6 of 17 2(b)(i) 4 M1: All charges M2: One octahedral with correct 3D M3: All formulae M4: R is cis, S is trans 2(b)(ii) dipoles cancel 1 2(c)(i) M1: (a species) that donates two lone pairs / forms two coordinate bonds / two dative bonds 2 M2: to a metal atom / metal ion © UCLES 2021 Page 7 of 17 2(c)(ii) 1 structure of the picolinate anion ligand 2(c)(iii) (coordination number) six 1 AND (geometry around Cr) octahedral 2(d)(i) (NH ) Cr O +6 1 4 2 2 7 Cr O +3 2 3 2(d)(ii) (NH ) Cr O → N + Cr O + 4H O 1 4 2 2 7 2 2 3 2 Question Answer Marks

4(a)(i) M1: blue solid / blue ppt 3 M2: [Cu(H O) ]2+ + 2OH– → Cu(OH) + 6H O 2 6 2 2 OR [Cu(H O) ]2+ + 2OH– → Cu(OH) (H O) + 2H O 2 6 2 2 4 2 M3: precipitation / acid-base 4(a)(ii) M1: dark blue solution / deep blue solution 3 M2: [Cu(H O) ]2+ + 4NH → [Cu(NH ) (H O) ]2+ + 4H O 2 6 3 3 4 2 2 2 M3: ligand exchange / substitution / displacement / replacement 4(b) M1: 2 X CuSO and Y Cu 4 M2: type of reaction = redox / disproportionation Question Answer Marks

5(a)(i) +2 [1] 1 5(a)(ii) 2 [1] bond angle labelled 109.5° [1] © UCLES 2021 Page 8 of 16 5(b)(i) [Co(H O) ]2+ + 2OH– → Co(H O) (OH) + 2H O OR [Co(H O) ]2+ + 2OH– → Co(OH) + 6H O [1] 2 2 6 2 4 2 2 2 6 2 2 blue precipitate [1] 5(b)(ii) [Co(H O) ]2+ + 6NH → [Co(NH ) ]2+ + 6H O [1] 2 2 6 3 3 6 2 yellow / brown / straw solution [1] 5(b)(iii) [Co(H O) ]2+ + 4Cl – → [CoCl ]2– + 6H O [1] 2 2 6 4 2 blue solution [1] 5(b)(iv) ligand exchange [1] 1 5(c)(i) (a species) that donates two lone pairs to form two dative bonds [1] 2 to a (transition) metal atom / metal ion [1] 5(c)(ii) 2 M1 one correct 3D structure – trans or cis [1] M2 a correct optical isomer of M1 [must 3D] [1] © UCLES 2021 Page 9 of 16

6(a) 2Cu2+ + 4I– → 2CuI + I OR 2CuSO + 4NaI → 2CuI + I + 2Na SO [1] 1 2 4 2 2 4 6(b)(i) M1: d-d orbital splitting occurs [1] 4 M2: electron(s) promoted / excited [1] M3: wavelength / frequency of light is absorbed [1] M4: colour seen is complementary OR wavelength / frequency of light not absorbed is seen [1] 6(b)(ii) (for Cu+) 3d10 OR 3d subshell full [1] 1 6(c) M1: (Cu2+ / Cu+) Eo = (+)0.15 V AND (I / I–) Eo = (+)0.54 V [1] 2 2 M2: No, since (Eo ) negative / –0.39 V cell OR No, since (I / I–) is more positive than (Cu2+ / Cu+) 2 OR No, I is more easily reduced OR No, I stronger oxidant ORA [1] 2 2 6(d) M1: Cu2+ / Cu+ E becomes more positive as equilibrium shifts to the right [1] 2 M2: The new E for Cu2+ / Cu+ is more positive than 0.54 / Eo (I / I–) [1] 2 © UCLES 2021 Page 10 of 16

5(a)(i) donates one lone pair / forms one dative bond AND to metal atom / to metal ion [1] 1 5(a)(ii) Mo(CO) 0 / no charge / neutral / zero 2 6 Fe(CN) 3– 6 both formulae [1] both charges [1] 5(a)(iii) either of these renditions, with a CN on each bond: 1 AND 180o bond angle between two opposite bonds [1] 5(b)(i) [Cu(H O) ]2+ + 4NH → [Cu(NH ) (H O) ]2+ + 4H O 1 2 6 3 3 4 2 2 2 OR Cu2+ + 2H O + 4NH → [Cu(NH ) (H O) ]2+ [1] 2 3 3 4 2 2 5(b)(ii) M1 d-orbitals split (could be in diagram) [1] 4 M2 electrons transition to higher orbital / electrons promoted or excited [1] M3 wavelength / frequency / light / photon / hf / hn absorbed [1] M4 colour seen / reflected / transmitted is complement of colour absorbed [1] © UCLES 2021 Page 8 of 12 5(c)(i) [Cu(NH ) (H O) ]2+ + 4HCl → CuCl 2– + 2H O + 4NH + 2 3 4 2 2 4 2 4 OR [Cu(NH ) (H O) ]2+ + 4Cl – (+ 4H+) → CuCl 2– + 2H O + 4NH (+ 4H+) 3 4 2 2 4 2 3 M1 formula and charge of CuCl 2– [1] 4 M2 rest of equation [1] 5(c)(ii) ligand exchange / substitution / replacement / displacement [1] 1 5(c)(iii) tetrahedral [1] 1 5(c)(iv) yellow [1] 1 5(c)(v) d-orbital splitting changes / ΔE changes [1] 1 Question Answer Marks

6(a) red or pink to yellow / straw / brown / orange [1] 1 6(b) [[Co(NH ) ]2+] / [[Co(H O) ]2+][NH ]6 [1] 1 3 6 2 6 3 6(c) Co(NH ) 2+ is more stable (than Co(H O) 2+) [1] 1 3 6 2 6 6(d)(i) Eo = + 0.30 [1] 1 cell 6(d)(ii) 4[Co(NH ) ]2+ + O + 2H O ⇌ 4[Co(NH ) ]3+ + 4OH– [1] 1 3 6 2 2 3 6 6(d)(iii) M1 No, because 1.82 V and 1.23 V [1] 2 M2 Eo = –0.59 / 1.23 lower than 1.82 / 1.82 greater than 1.2 [1] cell © UCLES 2021 Page 9 of 12

5(a)(i) +2 [1] 1 5(a)(ii) 2 [1] bond angle labelled 109.5° [1] © UCLES 2021 Page 8 of 16 5(b)(i) [Co(H O) ]2+ + 2OH– → Co(H O) (OH) + 2H O OR [Co(H O) ]2+ + 2OH– → Co(OH) + 6H O [1] 2 2 6 2 4 2 2 2 6 2 2 blue precipitate [1] 5(b)(ii) [Co(H O) ]2+ + 6NH → [Co(NH ) ]2+ + 6H O [1] 2 2 6 3 3 6 2 yellow / brown / straw solution [1] 5(b)(iii) [Co(H O) ]2+ + 4Cl – → [CoCl ]2– + 6H O [1] 2 2 6 4 2 blue solution [1] 5(b)(iv) ligand exchange [1] 1 5(c)(i) (a species) that donates two lone pairs to form two dative bonds [1] 2 to a (transition) metal atom / metal ion [1] 5(c)(ii) 2 M1 one correct 3D structure – trans or cis [1] M2 a correct optical isomer of M1 [must 3D] [1] © UCLES 2021 Page 9 of 16

6(a) 2Cu2+ + 4I– → 2CuI + I OR 2CuSO + 4NaI → 2CuI + I + 2Na SO [1] 1 2 4 2 2 4 6(b)(i) M1: d-d orbital splitting occurs [1] 4 M2: electron(s) promoted / excited [1] M3: wavelength / frequency of light is absorbed [1] M4: colour seen is complementary OR wavelength / frequency of light not absorbed is seen [1] 6(b)(ii) (for Cu+) 3d10 OR 3d subshell full [1] 1 6(c) M1: (Cu2+ / Cu+) Eo = (+)0.15 V AND (I / I–) Eo = (+)0.54 V [1] 2 2 M2: No, since (Eo ) negative / –0.39 V cell OR No, since (I / I–) is more positive than (Cu2+ / Cu+) 2 OR No, I is more easily reduced OR No, I stronger oxidant ORA [1] 2 2 6(d) M1: Cu2+ / Cu+ E becomes more positive as equilibrium shifts to the right [1] 2 M2: The new E for Cu2+ / Cu+ is more positive than 0.54 / Eo (I / I–) [1] 2 © UCLES 2021 Page 10 of 16

3(a)(i) (d-block) element that forms one or more stable ions with incomplete d subshell / incomplete d orbitals 1 © UCLES 2022 Page 6 of 12 3(a)(ii) • variable oxidation states 1 • behave as catalysts • form complex ions / complexes • form coloured compounds / ions Any two for one mark 3(b)(i) Ti is in +4 oxidation state so no d electrons / d0 OR Ti in TiO2+ has no d electrons / d0 [1] 2 cannot absorb photons / light in visible spectrum OR no wavelength / frequency absorbed in visible spectrum [1] 3(b)(ii) (1s2) 2s2 2p6 3s2 3p6 3d1 (4s0) 1 3(b)(iii) 2TiO2+ + 4H+ + Zn → 2Ti3+ + 2H O + Zn2+ 1 2 3(c)(i) M1: ∆G = – nE⦵ F AND n = 4 3 cell M2: ∴ E⦵ = –436100 / –4(96500) = 1.13 V ecf cell M3: E⦵ = E⦵(O ,4H+|H O) – E⦵(TiO2+|Ti3+) = 1.23 – E⦵(TiO2+|Ti3+) cell 2 2 ∴ E⦵(TiO2+|Ti3+) = (+)0.1 (V) ecf 3(c)(ii) Ti3+ empty / vacant d orbitals can form dative bonds / accept a lone pair from a ligand 1 OR Ti3+ has vacant d-orbitals which are energetically accessible 3(c)(iii) the E⦵ of the half-cell must be greater than +1.23 V / E⦵ of the O |H+ half-cell 1 2 as E⦵ < 0 and the reaction does not occur cell 3(d)(i) the number of co-ordinate bonds being formed by the metal atom/ion 1 3(d)(ii) TiO + 6HF → TiF 2– + 2H O + 2H+ 1 2 6 2 OR TiO + 6HF → TiF 2– + 2H O+ 2 6 3 3(d)(iii) species with two lone pairs (of electrons) [1] 2 that form dative covalent / co-ordinate bonds to a central metal atom/ion [1] © UCLES 2022 Page 7 of 12 3(d)(iv) mirror image of isomer I trans isomer 2 3(d)(v) isomer I AND cis isomer drawn by candidate ecf [1] 2 dipoles do not cancel / partial charges do not cancel [1] Question Answer Marks

2(a) forms one or more stable ions / compounds / oxidation states 1 with incomplete / partially filled (3)d-orbital(s) / d-shell / d-subshell 2(b) 1 OR 2(c)(i) the catalyst and the reactants are in a different state / phase 1 2(c)(ii) M1 adsorption of reactants to the surface of the catalyst 3 M2 bonds in the reactants weaken (lowering the activation energy) M3 reaction occurs and the products are desorbed © UCLES 2022 Page 6 of 15 2(d) M1 reaction 1: 2KMnO + H SO  Mn O + H O + K SO 2 4 2 4 2 7 2 2 4 OR 2KMnO + 2H SO  Mn O + H O + 2KHSO 4 2 4 2 7 2 4 M2 reaction 2: Mn O  2MnO + 1.5O 2 7 2 2 2(e)(i) M1 [Mn(H O) ]2+ + 2OH–  Mn(OH) + 6H O 2 2 6 2 2 M2 precipitation / acid-base / deprotonation 2(e)(ii) M1 [Mn(H O) ]2+ + 4Cl–  [MnCl ]2– + 6H O 2 2 6 4 2 M2 ligand exchange / substitution / replacement / displacement 2(e)(iii) MnO AND redox 1 2 Question Answer Marks

4(a)  five 3d orbitals in the isolated Fe2+ ion of same energy 2  splitting two higher and three lower d orbitals  energy of non-degenerate d orbitals in the complex more than degenerate d orbitals in isolated ion two for one mark, three for two marks 4(b)(i) M1 (a species) that donates / uses two lone pairs 2 M2 to form dative / coordinate bonds to a metal atom / metal ion / TM / TE / metal 4(b)(ii) 3 M1 one correct 3D diagram with three bipy ligands M2 both diagrams correct M3 optical isomerism 4(c) [Fe(CN) ]3– AND equilibrium lies most to the left / lowest Eo value 1 6 4(d) M1 N sp2 AND C sp2 3 M2  bonds are formed by end-on-end overlap orbitals between C-H / C-C / C-N M3  bonds are formed by sideways overlap of p orbitals between C-N / C-C © UCLES 2022 Page 9 of 15 4(e) 3 M1 first curly arrow to Cl+ M2 correct intermediate M3 second curly arrow AND H+ formed / lost Question Answer Marks

1(a) M1 H and H both become less exothermic / less negative 3 latt hyd M2 H changes less / becomes less exothermic by a smaller extent hyd OR H changes more / dominant factor / changes faster latt M3 H becomes more exothermic / more negative sol OR H becomes less endothermic / less positive sol 1(b)(i) M1 K = [Be2+][OH–]2 2 sp M2 mol3 dm–9 ecf 1(b)(ii) M1 solubility of Be(OH) = 2.40  10–6 / 43 = 5.58  10–8 (mol dm–3) ecf (b)(i) 2 2 M2 K = 4  (5.58  10–8)3 = 6.95  10–22 ecf min 2sf sp 1(c)(i) as a molecule or ion formed by a central metal atom / metal ion dative bonded to / surrounded by one or more ligands 1 1(c)(ii) 1 tetrahedral and correct 3D structure 1(d)(i) d orbitals that are energetically accessible 1 OR empty / vacant d orbitals AND form dative bonds / accept a lone pair from a ligand © UCLES 2022 Page 5 of 16 1(d)(ii) 2 coordination complex ion shape polarity number cis-[Pt(en)Cl ] square planar 4 polar 2 [Ag(NH ) ]+ linear 2 non-polar 3 2 [Fe(C O ) ]3- octahedral 6 non-polar 2 4 3 three for one mark, six for two marks 1(e)(i) the equilibrium constant for the formation of the complex ion in a solvent (from its constituent ions or molecules) 1 1(e)(ii) M1 K = [Ni(en) 2+] / [Ni(H O) 2+][en]3 2 stab 3 2 6 M1 units = mol–3 dm9 ecf 1(e)(iii) the equilibria lie to the right / product side OR equilibrium 1 lies more to the right 1 AND en complex is more stable / [Ni(en) ]2+ is more stable 3 Question Answer Marks

2(a) the d and s sub-shells / orbitals are close / similar in energy 1 2(b) 1 © UCLES 2022 Page 6 of 16 2(c) M1 (in a complex / in the presence of ligands) the d-orbitals are split into two sets of orbitals 3 M2 as an electron is excited / promoted M3 visible light is absorbed AND colour seen is complementary 2(d)(i) Cu(OH) : (pale / light) blue 1 2 [Cu(H O) (NH ) ]2+: dark / deep blue 2 2 3 4 2(d)(ii) (addition of OH–) increases [OH–] AND shifts equilibrium to the right 1 2(e) 2 M1 one correct 3D diagram with the six correct ligands M2 both 3D diagrams correct Question Answer Marks

2(a) forms one or more stable ions / compounds / oxidation states 1 with incomplete / partially filled (3)d-orbital(s) / d-shell / d-subshell 2(b) 1 OR 2(c)(i) the catalyst and the reactants are in a different state / phase 1 2(c)(ii) M1 adsorption of reactants to the surface of the catalyst 3 M2 bonds in the reactants weaken (lowering the activation energy) M3 reaction occurs and the products are desorbed © UCLES 2022 Page 6 of 15 2(d) M1 reaction 1: 2KMnO + H SO  Mn O + H O + K SO 2 4 2 4 2 7 2 2 4 OR 2KMnO + 2H SO  Mn O + H O + 2KHSO 4 2 4 2 7 2 4 M2 reaction 2: Mn O  2MnO + 1.5O 2 7 2 2 2(e)(i) M1 [Mn(H O) ]2+ + 2OH–  Mn(OH) + 6H O 2 2 6 2 2 M2 precipitation / acid-base / deprotonation 2(e)(ii) M1 [Mn(H O) ]2+ + 4Cl–  [MnCl ]2– + 6H O 2 2 6 4 2 M2 ligand exchange / substitution / replacement / displacement 2(e)(iii) MnO AND redox 1 2 Question Answer Marks

4(a)  five 3d orbitals in the isolated Fe2+ ion of same energy 2  splitting two higher and three lower d orbitals  energy of non-degenerate d orbitals in the complex more than degenerate d orbitals in isolated ion two for one mark, three for two marks 4(b)(i) M1 (a species) that donates / uses two lone pairs 2 M2 to form dative / coordinate bonds to a metal atom / metal ion / TM / TE / metal 4(b)(ii) 3 M1 one correct 3D diagram with three bipy ligands M2 both diagrams correct M3 optical isomerism 4(c) [Fe(CN) ]3– AND equilibrium lies most to the left / lowest Eo value 1 6 4(d) M1 N sp2 AND C sp2 3 M2  bonds are formed by end-on-end overlap orbitals between C-H / C-C / C-N M3  bonds are formed by sideways overlap of p orbitals between C-N / C-C © UCLES 2022 Page 9 of 15 4(e) 3 M1 first curly arrow to Cl+ M2 correct intermediate M3 second curly arrow AND H+ formed / lost Question Answer Marks

5(a) 1 3d 3d 2 xy z 5(b)(i) • d orbital(s) of different energy / d-d splitting occurs 4 • electron(s) promoted / excited • wavelength of visible light absorbed AND complementary colour seen • different energy gap / different E OR different frequency/wavelength of light is absorbed 5(b)(ii) 1 5(b)(iii) octahedral 1 AND optical isomerism 5(c) Fe2+ is smaller / has a smaller radius 2 OR Fe2+ greater charge density [1] polarises/distorts the anion / CO (2)– more [1] 3 5(d)(i) colourless / (pale) green to pink / purple 1 © UCLES 2022 Page 9 of 16 5(d)(ii) moles MnO – = 0.0100  0.0350 OR 3.50  10–4 2 4 moles Fe2+ = 5  3.50  10–4 OR 1.75  10–3 [1] moles Fe2+ = 1.75  10–3  4 = 7.00  10–3 % of Fe = (7.00  10–3  55.8) = 0.3906 g = 0.3906 / 2.62  100 = 14.9 % by mass [1] ecf M1 min 2sf Question Answer Marks

6(a)(i) [Cu(H O) ]2+ + 2OH– → [Cu(OH) (H O) ] + 2H O OR 1 2 6 2 2 4 2 OR [Cu(H O) ]2+ + 2NaOH → [Cu(OH) (H O) ] + 2H O + 2Na+ 2 6 2 2 4 2 6(a)(ii) [Cu(H O) ]2+ + 4Cl– → [CuCl ]2– + 6H O 1 2 6 4 2 OR [Cu(H O) ]2+ + 4HCl → [CuCl ]2– + 6H O + 4H+ 2 6 4 2 6(b)(i) 1 cis and trans drawn 6(b)(ii) cis identified as polar AND trans identified as non-polar 1 conditional on diagram 6(c)(i) the equilibrium (constant) for the formation of the complex ion in a solvent from its constituent ions or molecules 1 6(c)(ii) [Cu(NH ) (H O) ]2+ AND as K is large OWTTE 1 3 4 2 2 stab 6(c)(iii) K = [[Cu(NH ) (H O) ]2+] / [[Cu(H O) ]2+] [NH ]4 [1] 2 stab 3 4 2 2 2 6 3 mol–4 dm12 [1] ecf M1 © UCLES 2022 Page 10 of 16 6(c)(iv) [Cu(H O) ]2+] = (0.0074) ÷ (1.4  1013  0.574) 1 2 6 [Cu(H O) ]2+] = 5.01  10–15 min 2sf ecf 6(c)(iii) 2 6 6(d) [Ru(C H N ) Cl ]+ [1] 2 12 8 2 2 2 [Fe(C O ) ]3– [1] 2 4 3 Question Answer Marks

5(a) a d-block element that forms one or more stable ions with incomplete d-orbitals 1 5(b)(i) 3 geometry CN bond angle [Cu(H O) ]2+ octahedral 6 90 or 180 2 6 [CuCl ]2– tetrahedral 4 109 to 110 4 5(b)(ii) degenerate – of the same energy 1 non-degenerate – not of the same energy / different energy 5(b)(iii) different frequency / wavelength / photon absorbed 1 © UCLES 2022 Page 7 of 11 5(c)(i) forms 2 dative / coordinate bonds 1 5(c)(ii) one isomer correct with correct 3D [1] 2 three isomers different with correct 3D [1] 5(c)(iii) e.g. 1 and 2 optical [1] 2 e.g. 1 or 2 and 3 cis-trans / geometric [1] 5(d) 0.0230 moles ethanedioate in whole 100 cm3 3 0.00575 moles ethanedioate in 25 cm3 sample [1] 0.00230 moles of MnO – needed [1] 4 230 cm3 [1] 5(e) Cu2+ is smaller / has a smaller radius / than Ba2+ [1] 2 Cu2+ polarises / distorts the anion more [1] Question Answer Marks

6(a)(i) 2 blue or pink s / solid blue aq / aqueous two cells correct [1] two more cells correct [1] 6(a)(ii) [Co(H O) ]2+ + 2OH– → Co(OH) + 6H O or 1 2 6 2 2 [Co(H O) ]2+ + 2OH– → Co(H O) (OH) + 2H O 2 6 2 4 2 2 6(a)(iii) [Co(H O) ]2+ + 4Cl– → [CoCl ]2– + 6H O 1 2 6 4 2 6(b)(i) the equilibrium constant for the formation of a complex ion in a solvent OR the equilibrium constant for the formation of a 1 complex ion from its constituent ions © UCLES 2022 Page 8 of 11 6(b)(ii) K = [[Co(NH ) ]2+] / [[Co(H O) ]2+][NH ]6 1 stab 3 6 2 6 3 or [[Co(NH ) ]2+] / [Co2+][NH ]6 3 6 3 6(b)(iii) mol–6 dm18 1 6(b)(iv) 7.86  10–5 1 Question Answer Marks

5(a) 1 3d 3d 2 xy z 5(b)(i) • d orbital(s) of different energy / d-d splitting occurs 4 • electron(s) promoted / excited • wavelength of visible light absorbed AND complementary colour seen • different energy gap / different E OR different frequency/wavelength of light is absorbed 5(b)(ii) 1 5(b)(iii) octahedral 1 AND optical isomerism 5(c) Fe2+ is smaller / has a smaller radius 2 OR Fe2+ greater charge density [1] polarises/distorts the anion / CO (2)– more [1] 3 5(d)(i) colourless / (pale) green to pink / purple 1 © UCLES 2022 Page 9 of 16 5(d)(ii) moles MnO – = 0.0100  0.0350 OR 3.50  10–4 2 4 moles Fe2+ = 5  3.50  10–4 OR 1.75  10–3 [1] moles Fe2+ = 1.75  10–3  4 = 7.00  10–3 % of Fe = (7.00  10–3  55.8) = 0.3906 g = 0.3906 / 2.62  100 = 14.9 % by mass [1] ecf M1 min 2sf Question Answer Marks

6(a)(i) [Cu(H O) ]2+ + 2OH– → [Cu(OH) (H O) ] + 2H O OR 1 2 6 2 2 4 2 OR [Cu(H O) ]2+ + 2NaOH → [Cu(OH) (H O) ] + 2H O + 2Na+ 2 6 2 2 4 2 6(a)(ii) [Cu(H O) ]2+ + 4Cl– → [CuCl ]2– + 6H O 1 2 6 4 2 OR [Cu(H O) ]2+ + 4HCl → [CuCl ]2– + 6H O + 4H+ 2 6 4 2 6(b)(i) 1 cis and trans drawn 6(b)(ii) cis identified as polar AND trans identified as non-polar 1 conditional on diagram 6(c)(i) the equilibrium (constant) for the formation of the complex ion in a solvent from its constituent ions or molecules 1 6(c)(ii) [Cu(NH ) (H O) ]2+ AND as K is large OWTTE 1 3 4 2 2 stab 6(c)(iii) K = [[Cu(NH ) (H O) ]2+] / [[Cu(H O) ]2+] [NH ]4 [1] 2 stab 3 4 2 2 2 6 3 mol–4 dm12 [1] ecf M1 © UCLES 2022 Page 10 of 16 6(c)(iv) [Cu(H O) ]2+] = (0.0074) ÷ (1.4  1013  0.574) 1 2 6 [Cu(H O) ]2+] = 5.01  10–15 min 2sf ecf 6(c)(iii) 2 6 6(d) [Ru(C H N ) Cl ]+ [1] 2 12 8 2 2 2 [Fe(C O ) ]3– [1] 2 4 3 Question Answer Marks

3(a) (a d-block element forms one or more) 1 stable ions with incomplete filled d-subshell 3(b)(i) • they behave as catalysts 1 • they form complex ions / complexes • they form coloured compounds / salts / ions any two 3(b)(ii) the d and s sub-shells/orbitals 1 are close/similar in energy 3(c)(i) 0.02500  0.0300 OR 7.50  10–4 mol VO + 1 2 OR ½(28.15 + 28.10)/1000  0.0400 OR 1.13  10–3 mol C O 2– 2 4 Use of their values to show ratio of VO + : C O 2– = 1:1.5 1 2 2 4 ALLOW any viable approach © UCLES 2023 Page 8 of 17 3(c)(ii) 1 3D structure charge 1 3(d)(i) VO + AND E⦵ of H O is largest / most positive value 1 2 2 2 OR VO + AND E⦵ is less positive than H O 2 2 2 3(d)(ii) +5 1 Question Answer Marks

1(a) M1 increases (down the group) 3 M2 radius / size of (cat)ion / M2+ increases M3 less polarisation / distortion of anion / nitrate ion / NO – OR less weakening of N–O / N=O (bond) 3 1(b) Cu(NO )  CuO + 2NO + ½O 1 3 2 2 2 1(c) 4 copper- formula of copper-containing colour copper- containing species formed containing formed species A [Cu(H O) ]2+ (pale) blue 2 6 B Cu(H O) (OH) or Cu(OH) (pale) blue 2 4 2 2 C [Cu(NH ) (H O) ]2+ dark blue 3 4 2 2 D CuCl 2– yellow 4 Two correct for one mark, four correct for two marks, six correct for three marks, eight correct for four marks. 1(d)(i) M1 (a species) that donates more than two lone pairs 2 M2 to form dative / coordinate bonds to a metal atom or ion 1(d)(ii) six atoms circled, 2N and 4O from different CO – 1 2 1(d)(iii) the number of co-ordinate bonds being formed by the metal ion 1 1(d)(iv) ligand exchange 1 1(d)(v) [FeEDTA]– > [CrEDTA]– > [PbEDTA]2– 1 highest concn lowest concn AND K of [FeEDTA]– is highest stab © UCLES 2023 Page 6 of 17 1(e) M1 moles of Cr3+ = 2.096  10–4 in 25.0 cm3) 3 M2 moles of Cr3+ = 8.384  10–4 (in 100.0 cm3) moles of Cr (SO ) nH O = 8.384  10–4 / 2 = 4.192  10–4 2 4 3 2 M3 M of Cr (SO ) nH O = 0.2550 / 4.192  10–4 = 608.3 r 2 4 3 2 n = (608.3 – 392.3) / 18 = 12 1(f) M1 E is different 2 M2 different frequency (of light) is absorbed Question Answer Marks

2(a) Any two from: 1  they have variable / multiple oxidation states OWTTE  they behave as catalysts  they form complex ions / complexes  they form coloured compounds/ions 2(b)(i) (is a molecule or ion formed by a central) metal atom / metal ion bonded / surrounded by (one or more) ligands 1 © UCLES 2023 Page 7 of 19 2(b)(ii) 4 formula of colour / state of reagent added type of reaction species formed species formed brown solution an excess of ligand [Co(NH ) ]2+ ALLOW yellow- NH (aq) 3 6 exchange 3 brown solution an excess of ligand [CoCl ]2– blue solution concentrated HCl 4 exchange Co(OH) 2 blue ppt. NaOH(aq) OR precipitation ALLOW pink ppt Co(OH) (H O) 2 2 4 formula and colour / state: any two [1], any four [2], all six [3] type of reaction: all three correct [1] 2(c)(i) M1 (a species) that donates / uses two lone pairs 2 M2 to form a two dative / coordinate bond to a metal atom / metal ion © UCLES 2023 Page 8 of 19 2(c)(ii) Any four from: 3 Any two [1], any three [2], all four [3] 2(c)(iii) oxidation state of cobalt (+)3 1 AND type of stereoisomerism cis-trans OR geometric(al) OR optical © UCLES 2023 Page 9 of 19

1(a) M1 increases (down the group) 3 M2 radius / size of (cat)ion / M2+ increases M3 less polarisation / distortion of anion / nitrate ion / NO – OR less weakening of N–O / N=O (bond) 3 1(b) Cu(NO )  CuO + 2NO + ½O 1 3 2 2 2 1(c) 4 copper- formula of copper-containing colour copper- containing species formed containing formed species A [Cu(H O) ]2+ (pale) blue 2 6 B Cu(H O) (OH) or Cu(OH) (pale) blue 2 4 2 2 C [Cu(NH ) (H O) ]2+ dark blue 3 4 2 2 D CuCl 2– yellow 4 Two correct for one mark, four correct for two marks, six correct for three marks, eight correct for four marks. 1(d)(i) M1 (a species) that donates more than two lone pairs 2 M2 to form dative / coordinate bonds to a metal atom or ion 1(d)(ii) six atoms circled, 2N and 4O from different CO – 1 2 1(d)(iii) the number of co-ordinate bonds being formed by the metal ion 1 1(d)(iv) ligand exchange 1 1(d)(v) [FeEDTA]– > [CrEDTA]– > [PbEDTA]2– 1 highest concn lowest concn AND K of [FeEDTA]– is highest stab © UCLES 2023 Page 6 of 17 1(e) M1 moles of Cr3+ = 2.096  10–4 in 25.0 cm3) 3 M2 moles of Cr3+ = 8.384  10–4 (in 100.0 cm3) moles of Cr (SO ) nH O = 8.384  10–4 / 2 = 4.192  10–4 2 4 3 2 M3 M of Cr (SO ) nH O = 0.2550 / 4.192  10–4 = 608.3 r 2 4 3 2 n = (608.3 – 392.3) / 18 = 12 1(f) M1 E is different 2 M2 different frequency (of light) is absorbed Question Answer Marks

5(a) more than one (stable) oxidation state [1] 2 empty / vacant (d) orbitals are energetically accessible OR empty / vacant (d) orbitals can form dative bonds with ligands [1] 5(b)(i) oxid. no. = + 4 AND 1 coord. no. = 8 [1] © UCLES 2023 Page 10 of 18 5(b)(ii) bond angle must go from bond to bond 2 OR CN group to CN group diagram • for Ag: NC—Ag—CN • angle = labelled 180° • for Cu: • angle = labelled 109–110° any two [1] all four [2] 5(c)(i) K = [[Cu(CN) ]3–] / [Cu+] [CN–]4 [1] 1 stab 4 ALLOW use of [[Cu(H O) ]+] 2 6 5(c)(ii) [Cu+] = 5.0  10–19 (mol dm–3) [1] min 1sf 1 ECF from reversed ratio 5(c)(i) 5(d)(i) mol of I = 0.5  0.02  20.1 / 1000 = 2.01  10–4 [1] min 2sf 1 2 5(d)(ii) mol of Cu = 2.01  10–4  2  4 = 1.608 / 1.61  10–3 [1] ecf min 2sf 1 5(d)(iii) % of Cu = 100  (1.60810–3  63.5) / 0.567 = 18.0 [1] ecf 1 5(d)(iv) Cu2+ is d9 / d shell / sub-shell / orbitals is / are not full 2 AND Cu+ is d10 / d shell / sub-shell / orbitals is / are full [1] d-d* transitions / d electron promotion not possible / possible (linked correctly) [1] © UCLES 2023 Page 11 of 18

6(a)(i) NH = monodentate 2 3 EDTA4– = polydentate / hexadentate CN– = monodentate C O 2– = bidentate 2 4 any two [1] all four [2] 6(a)(ii) (ligand that) donates 3 lone pairs to central metal atom / ion 1 OR (ligand that) forms 3 dative bonds to central metal atom / ion [1] 6(a)(iii) ref to using the electrons / lone pair on (each) N / amine group [1] 1 6(b)(i) trans = non-polar 1 cis isomer 1 = polar cis isomer 2 = polar ALL [1] 6(b)(ii) optical isomers / non-superimposable mirror images [1] 1 ALLOW enantiomers / they rotate polarised light differently Question Answer Marks

4(a) equilibrium constant for the formation of a complex in a solvent / 1 from its constituents [1] 4(b) +2 AND + 3 [1] 1 4(c) Six [1] 1 4(d) [Fe(EDTA)]– AND largest K [1] 1 stab 4(e) [[CuEDTA]2–] ÷ ([[Cu(H O) ]2+]  [EDTA2–]) = 6.311019 [1] 2 2 6 0.095 [1] 4(f) different E OR different energy gap between d-orbitals [1] 2 absorption of different wavelength OR absorption of different frequency [1] Question Answer Marks

6(a)(i) donates one lp to metal atom or ion [1] 1 6(a)(ii) metal atom or ion bonded to one or more ligands [1] 1 6(a)(iii) has vacant d-orbitals which are energetically accessible [1] 1 6(b)(i) octahedral 1 square planar octahedral [1] 6(b(ii) [Au(dien)(H O) Cl]2+ + 2Cl– → [Au(dien)Cl ] + 2H O [1] 1 2 2 3 2 OR [Au(dien)Cl ] + 2H O → [Au(dien)(H O) Cl]2+ + 2Cl– 3 2 2 2 6(b)(iii) [1] © UCLES 2023 Page 8 of 14 6(b)(iv) 1 [1] 6(b)(v) [Rh(en) Cl ]+ AND 1 2 2 optical AND cis / trans OR geometric [1] 6(b)(vi) 2 [1] cis/trans OR geometric [1] Question Answer Marks

5(a) more than one (stable) oxidation state [1] 2 empty / vacant (d) orbitals are energetically accessible OR empty / vacant (d) orbitals can form dative bonds with ligands [1] 5(b)(i) oxid. no. = + 4 AND 1 coord. no. = 8 [1] © UCLES 2023 Page 10 of 18 5(b)(ii) bond angle must go from bond to bond 2 OR CN group to CN group diagram • for Ag: NC—Ag—CN • angle = labelled 180° • for Cu: • angle = labelled 109–110° any two [1] all four [2] 5(c)(i) K = [[Cu(CN) ]3–] / [Cu+] [CN–]4 [1] 1 stab 4 ALLOW use of [[Cu(H O) ]+] 2 6 5(c)(ii) [Cu+] = 5.0  10–19 (mol dm–3) [1] min 1sf 1 ECF from reversed ratio 5(c)(i) 5(d)(i) mol of I = 0.5  0.02  20.1 / 1000 = 2.01  10–4 [1] min 2sf 1 2 5(d)(ii) mol of Cu = 2.01  10–4  2  4 = 1.608 / 1.61  10–3 [1] ecf min 2sf 1 5(d)(iii) % of Cu = 100  (1.60810–3  63.5) / 0.567 = 18.0 [1] ecf 1 5(d)(iv) Cu2+ is d9 / d shell / sub-shell / orbitals is / are not full 2 AND Cu+ is d10 / d shell / sub-shell / orbitals is / are full [1] d-d* transitions / d electron promotion not possible / possible (linked correctly) [1] © UCLES 2023 Page 11 of 18

6(a)(i) NH = monodentate 2 3 EDTA4– = polydentate / hexadentate CN– = monodentate C O 2– = bidentate 2 4 any two [1] all four [2] 6(a)(ii) (ligand that) donates 3 lone pairs to central metal atom / ion 1 OR (ligand that) forms 3 dative bonds to central metal atom / ion [1] 6(a)(iii) ref to using the electrons / lone pair on (each) N / amine group [1] 1 6(b)(i) trans = non-polar 1 cis isomer 1 = polar cis isomer 2 = polar ALL [1] 6(b)(ii) optical isomers / non-superimposable mirror images [1] 1 ALLOW enantiomers / they rotate polarised light differently Question Answer Marks

3(a)(i) energies / energy levels of the 3d and the 4s (sub-shells / orbitals) are similar 1 OR the difference between the 3d and the 4s is small 3(a)(ii) Fe = [Ar] 3d6 4s2 AND 1 Fe3+ = [Ar] 3d5 3(b)(i) (a molecule or ion formed by a central) metal atom / ion 1 surrounded / bonded by one or more ligands 3(b)(ii) 6 / six 1 3(b)(iii) bond angle 106–108° 1 AND lone pair from O is donated (in a bond) OR one more of O’s electron pairs is now a bond/bonding pair (so repels less) 3(b)(iv) M1 (degenerate) d orbitals split (into two energy levels) 1 OR (degenerate) d orbitals become non-degenerate M2 as an electron moves up / to a higher energy level 1 M3 absorption of light energy / energy in the visible region 1 AND colour seen is complementary (to colour absorbed) 3(b)(v) (d–d) energy gap / E /  is different 1 oct different frequency / wavelength (of light) absorbed / transmitted / reflected 1 3(c)(i) [Fe(H O) ]3+ + H PO → [Fe(H O) (H PO )]2+ + H O+ 1 2 6 3 4 2 5 2 4 3 © Cambridge University Press & Assessment 2024 Page 8 of 13 3(c)(ii) [[Fe(H O) (SCN)]2+] 1 K = 2 5 stab [[Fe(H O) ]3+][SCN–] 2 6 mol–1 dm3 u/c 1 3(c)(iii) 1.30  102 / 59.0 = 2.2(03) min 2sf 1 Question Answer Marks

4(a)(i) X [Ru(H 2 O) 5 Cl ]2+ 1 Y [Ru(H 2 O) 4 Cl2 ]+ ECF [1] if reversed 1 4(a)(ii) 2 4(b)(i) (pyrazine has) a lone pair on each N (atoms) / two lone pairs (on the N’s) 1 AND which can be donated / form a coordinate / dative bond (with Ru) 4(b)(ii) • shape is (hexagonal ring) planar / (trigonal) planar / 120o 2 • carbons and nitrogens are sp2hybridised • a p orbital (from each atom) overlaps sideways/laterally (with each other above and below the ring forming  bonds) mark as  ✓ ✓ © Cambridge University Press & Assessment 2024 Page 9 of 13 4(b)(iii) 1/one 1 all the carbon atoms are equivalent / in same environment 1 OR pyrazine is a symmetrical molecule u/c 4(b)(iv) +2 / 2+ AND +3 / 3+ OR +4 / 4+ AND +1 / 1+ 1 4(c)(i) SOCl2 OR PCl3 OR PCl5 1 4(c)(ii) M1 correct ester linkage in the middle of the polymer 1 (displayed C=O bond attached to benzene ring) M2 rest of structure 1 Question Answer Marks

2(a)(i) element which forms one or more stable ion with incomplete d orbitals 1 2(a)(ii) they have vacant d orbitals that are energetically accessible 1 2(b)(i) orbitals of the same energy 1 2(b)(ii) 1 © Cambridge University Press & Assessment 2024 Page 5 of 18 2(c) M1 2AgNO + 2NaOH → Ag O + 2NaNO + H O 2 3 2 3 2 OR 2Ag+ + 2OH– → Ag O + H O 2 2 M2 Ag O + 4NH + H O → 2[Ag(NH ) ]OH 2 3 2 3 2 OR Ag+ + 2NH + OH– → [Ag(NH ) ]OH 3 3 2 2(d) M1 bond angle H–N–Ag is 109.5° 2 M2 shape is linear AND bond angle for N–Ag–N is 180° 2(e) M1 Ag O + H O + 2e– → 2Ag + 2OH– 2 2 2 M2 Zn + 2OH– → Zn(OH) + 2e– 2 2(f) For example: 2 M1 presence of dps ligand bonded to two Ru M2 the rest of the structure correct © Cambridge University Press & Assessment 2024 Page 6 of 18

3(a) Li C O H O → Li CO + H O + CO 1 2 2 4 2 2 3 2 3(b) M1 CaC O AND Ca2+has a smaller ionic radius / Ca2+has a higher charge density 2 2 4 M2 anion / C O 2– becomes more polarised / distorted 2 4 3(c) M1 d orbital(s) of different energy / d-d splitting occurs 3 M2 electron(s) promoted / excited M3 light is absorbed AND colour seen is complementary 3(d) 2K Fe(C O ) → 2K Fe(C O ) + K C O + 2CO 1 3 2 4 3 2 2 4 2 2 2 4 2 3(e) 2 3(f) M1 HC O – + H+ → H C O 2 2 4 2 2 4 M2 HC O – + OH– → C O 2–+ H O 2 4 2 4 2 3(g) M1 2C O 2– + O (g) + 2H O(l) → 4CO (g) + 4OH–(aq) 2 2 4 2 2 2 M2 E = 0.40 – (–0.59) = 0.99 V cell © Cambridge University Press & Assessment 2024 Page 7 of 18

4(a)(i) the (3)d and (4)s (sub-shells/orbitals) are close/similar in energy 1 4(a)(ii) 1 © Cambridge University Press & Assessment 2024 Page 7 of 15 4(b)  precipitation solution A: e.g. NaOH / OH– 3  observations: (pale) blue ppt. / solid  product: Cu(OH) OR [Cu(OH) (H O) ] ecf from A 2 2 2 4  ligand substitution solution B: e.g. HCl / Cl –, NH 3  observations: dark/deep blue solution (with NH ) OR yellow solution (with Cl –) 3  product: [Cu(NH ) (H O) ]2+ OR [CuCl ]2– 3 4 2 2 4 any two [1] any four [2] all six [3] 4(c) M1 (Ag+) d-subshell is full / complete OR d10 OR d-orbitals are full 2 M2 no d-d(*) transition OR no d electrons promoted/excited 4(d) M1 species with two lone pairs (of electrons) 2 M2 that form dative (covalent) / co-ordinate bond(s) to a (central) metal atom / ion 4(e)(i) 3 4(e)(ii) optical AND cis-trans / geometical 1 4(e)(iii) trans isomer / trans isomer correctly identified AND dipoles cancel / partial charges cancel / ion dipoles cancel 1 © Cambridge University Press & Assessment 2024 Page 8 of 15

2(a)(i) element which forms one or more stable ion with incomplete d orbitals 1 2(a)(ii) they have vacant d orbitals that are energetically accessible 1 2(b)(i) orbitals of the same energy 1 2(b)(ii) 1 © Cambridge University Press & Assessment 2024 Page 5 of 18 2(c) M1 2AgNO + 2NaOH → Ag O + 2NaNO + H O 2 3 2 3 2 OR 2Ag+ + 2OH– → Ag O + H O 2 2 M2 Ag O + 4NH + H O → 2[Ag(NH ) ]OH 2 3 2 3 2 OR Ag+ + 2NH + OH– → [Ag(NH ) ]OH 3 3 2 2(d) M1 bond angle H–N–Ag is 109.5° 2 M2 shape is linear AND bond angle for N–Ag–N is 180° 2(e) M1 Ag O + H O + 2e– → 2Ag + 2OH– 2 2 2 M2 Zn + 2OH– → Zn(OH) + 2e– 2 2(f) For example: 2 M1 presence of dps ligand bonded to two Ru M2 the rest of the structure correct © Cambridge University Press & Assessment 2024 Page 6 of 18

3(a) Li C O H O → Li CO + H O + CO 1 2 2 4 2 2 3 2 3(b) M1 CaC O AND Ca2+has a smaller ionic radius / Ca2+has a higher charge density 2 2 4 M2 anion / C O 2– becomes more polarised / distorted 2 4 3(c) M1 d orbital(s) of different energy / d-d splitting occurs 3 M2 electron(s) promoted / excited M3 light is absorbed AND colour seen is complementary 3(d) 2K Fe(C O ) → 2K Fe(C O ) + K C O + 2CO 1 3 2 4 3 2 2 4 2 2 2 4 2 3(e) 2 3(f) M1 HC O – + H+ → H C O 2 2 4 2 2 4 M2 HC O – + OH– → C O 2–+ H O 2 4 2 4 2 3(g) M1 2C O 2– + O (g) + 2H O(l) → 4CO (g) + 4OH–(aq) 2 2 4 2 2 2 M2 E = 0.40 – (–0.59) = 0.99 V cell © Cambridge University Press & Assessment 2024 Page 7 of 18

4(a) empty (d) orbitals are energetically accessible 1 OR empty (d) orbitals can form dative bonds with ligands OR empty (d) orbitals can accept a lone pair from ligands [1] 4(b)(i) [Co O NH (NH ) ]3+ scores [2] must have Co 2 2 2 2 3 8 2 • Co O NH 2 2 2 • 8 ammonia so both Co are octahedral (ecf bullet 1) • correct charge based on ligands present (ecf Co and NH ) 2 any two [1] all three [2] 4(b)(ii) 2 1 3 BOTH [1] 4(b)(iii) E different OR (d–d) energy gap different [1] 2 different frequency/wavelength/energy from visible light absorbed [1] © Cambridge University Press & Assessment 2024 Page 9 of 14 4(c)(i) [Cd(NH ) ]2+ + 4CN– → [Cd(CN) ]2– + 4NH 2 3 4 4 3 X Y complex formed is [Cd(CN) ]2– / Na [Cd(CN) ] [1] equation fully correct 4 2 4 [1] ECF 4(c)(ii) [CdCl ]2– [Cd(NH ) ]2+ [Cd(CN) ]2– 1 4 3 4 4 OR Z X Y [1] 4(d)(i) Cr O 2– + 8H+ + 3HOOCCOOH → 2Cr3+ + 7H O + 6CO [1] 1 2 7 2 2 4(d)(ii) • mol Cr O 2– = 0.0500  16.20 / 1000 = 8.10  10–4 2 2 7 • mol HOOCCOOH / C O 2– = 8.10  10–4  3 = 2.43  10–3 ecf 2 4 • [C O 2–] = 2.43  10–3  40 = 0.0972 mol dm–3 min 2sf ecf 2 4  ✓ ✓ [2] Question Answer Marks

5(a) bond angle must go from bond to bond 2 P 109 OR 109.5° Q 90° (or 180° if different angle labelled) R 90° (or 180° if different angle labelled) S 180° any two [1] all four [2] 5(b) P tetrahedral 2 Q square planar R octahedral S linear any two [1] all four [2] 5(c) Q AND R [1] 1 5(d) P AND R [1] 1 © Cambridge University Press & Assessment 2024 Page 10 of 14

4(a)(i) red/pink blue [1] 1 4(a)(ii) [Co(H O) ]2+ + 2OH– → Co(H O) (OH) + 2H O [1] 1 2 6 2 4 2 2 4(a)(iii) acid-base [1] 1 4(b)(i) [CoL ]2+ [1] 1 2 © Cambridge University Press & Assessment 2024 Page 7 of 12 4(b)(ii) +2 [1] 1 4(b)(iii) 2 1 3 [1] 4(b)(iv) Not of the same energy / have different energy [1] 1 4(c)(i) 5Fe2+ + MnO – + 8H+ → 5Fe3+ + Mn2+ + 4H O [1] 1 4 2 4(c)(ii) 0.02  18.7/1000 = 3.74  10–4 [1] 2 3.74  10–4  5 = 1.87  10–3 [1] 4(c)(iii) 1.87  10–3  10 = 1.87  10–2 2 4.18/1.87  10–2 = 224 / 223.5(294) [1] n = 2 [1] Question Answer Marks

5(a) [[Ni(en) ]2+] [[Ni(en) ]2+] 1 K = 3 OR 3 [1] stab [Ni2+][en]3 [Ni(H O) 2+][en]3 2 6 5(b)(i) [Ni(en) ]2+ AND 1 3 larger K OR more stable [1] stab 5(b)(ii) [Ni(H O) ]2+ + 3en → [Nien ]2+ + 6H O [1] 1 2 6 3 2 © Cambridge University Press & Assessment 2024 Page 8 of 12 5(c) 3 octahedral with correct 3D for one [Ni(en) ]2+ [1] 3 second optical isomer [1] optical isomerism [1] Question Answer Marks

4(a) empty (d) orbitals are energetically accessible 1 OR empty (d) orbitals can form dative bonds with ligands OR empty (d) orbitals can accept a lone pair from ligands [1] 4(b)(i) [Co O NH (NH ) ]3+ scores [2] must have Co 2 2 2 2 3 8 2 • Co O NH 2 2 2 • 8 ammonia so both Co are octahedral (ecf bullet 1) • correct charge based on ligands present (ecf Co and NH ) 2 any two [1] all three [2] 4(b)(ii) 2 1 3 BOTH [1] 4(b)(iii) E different OR (d–d) energy gap different [1] 2 different frequency/wavelength/energy from visible light absorbed [1] © Cambridge University Press & Assessment 2024 Page 9 of 14 4(c)(i) [Cd(NH ) ]2+ + 4CN– → [Cd(CN) ]2– + 4NH 2 3 4 4 3 X Y complex formed is [Cd(CN) ]2– / Na [Cd(CN) ] [1] equation fully correct 4 2 4 [1] ECF 4(c)(ii) [CdCl ]2– [Cd(NH ) ]2+ [Cd(CN) ]2– 1 4 3 4 4 OR Z X Y [1] 4(d)(i) Cr O 2– + 8H+ + 3HOOCCOOH → 2Cr3+ + 7H O + 6CO [1] 1 2 7 2 2 4(d)(ii) • mol Cr O 2– = 0.0500  16.20 / 1000 = 8.10  10–4 2 2 7 • mol HOOCCOOH / C O 2– = 8.10  10–4  3 = 2.43  10–3 ecf 2 4 • [C O 2–] = 2.43  10–3  40 = 0.0972 mol dm–3 min 2sf ecf 2 4  ✓ ✓ [2] Question Answer Marks

5(a) bond angle must go from bond to bond 2 P 109 OR 109.5° Q 90° (or 180° if different angle labelled) R 90° (or 180° if different angle labelled) S 180° any two [1] all four [2] 5(b) P tetrahedral 2 Q square planar R octahedral S linear any two [1] all four [2] 5(c) Q AND R [1] 1 5(d) P AND R [1] 1 © Cambridge University Press & Assessment 2024 Page 10 of 14

3(a)(i) (central) metal / transition element atom / ion 1 AND surrounded by / bonded to ligands © Cambridge University Press & Assessment 2025 Page 7 of 14 3(a)(ii) 3 coordination formula and charge complex ion ligand number of complex E Fe2+ NH 6 [Fe(NH ) ]2+ 3 3 6 F Fe2+ Cl– 4 [FeCl4 ]2– G Fe3+ en 6 [Fe(en) ]3+ 3 any two [1] any four [2] all six [3] 3(a)(iii) three(3) higher AND two(2) lower boxes / energy levels 1 3(b)(i) d–d energy gap / E is different 1 ) different frequency / wavelength (of light) absorbed / transmitted / reflected 1 3(b)(ii) [[Fe(H O) SCN]2+] 1 K = 2 5 stab [[Fe(H O) ]3+] [SCN]−] 2 6 3(b)(iii) K = 2.40  105 / 1.40  102 = 1714 min 2sf 1 c 3(b)(iv) M1: solution turns (violet / purple to) colourless 2 AND solution then remains / stays colourless / no change M2: K of [Fe(H O) F]2+ > [Fe(H O) SCN]2+ stab 2 5 2 5 OR [Fe(H O) F]2+ is most stable (more stable than [Fe(H O) SCN]2+) 2 5 2 5 © Cambridge University Press & Assessment 2025 Page 8 of 14 3(c)(i) C O 2– → 2CO + 2e– 2 2 4 2 MnO – + 8H+ + 5e– → Mn2+ + 4H O 4 2 3(c)(ii) M1 moles of manganate = 12.20 / 1000  0.0200 = 2.44  10–4 mol 4 AND moles of ethanedioate = 5 / 2  2.44  10–4 = 6.10  10–4 mol M2 moles of K Fe(C O ) = 6.10  10–4 ÷ 3 = 2.03  10–4 mol 3 2 4 3 AND mass of K Fe(C O ) = 437.1  2.03  10–4 = 0.0889 g 3 2 4 3 M3 mass of water = 0.100 – 0.0889 = 0.0111 g AND moles of water = 0.0111 / 18.0 = 6.18  10–4 mol M4 x = molar ratio = 6.18  10–4 / 2.03  10–4 = 3 Question Answer Marks

6(a)(i) [Fe(CN) ]3– AND [Fe(CN) ]4– 1 6 6 6(a)(ii) M1: different E 2 M2: absorption of different frequency of visible light OR wavelength of visible light 6(a)(iii) dative covalent / coordinate 1 © Cambridge University Press & Assessment 2025 Page 10 of 16 6(b) 4 Each correct structure = [1] © Cambridge University Press & Assessment 2025 Page 11 of 16

6(a)(i) [Fe(CN) ]3– AND [Fe(CN) ]4– 1 6 6 6(a)(ii) M1: different E 2 M2: absorption of different frequency of visible light OR wavelength of visible light 6(a)(iii) dative covalent / coordinate 1 © Cambridge University Press & Assessment 2025 Page 10 of 16 6(b) 4 Each correct structure = [1] © Cambridge University Press & Assessment 2025 Page 11 of 16

1(a)(i) M1: (thermal stability) increases (down the group or from Mg to Ba) 3 OR carbonates become more stable (down the group or from Mg to Ba) M2: ion / cation size / radius increases OR charge density on ion / cation decreases M3: less polarised CO (2)– / anion / carbonate ion 3 OR weakens the C-O / C=O / covalent bonds less OR weakens bonds in the anion less OR lattice enthalpy of MO falls (less exothermic) faster than MCO (due to differing sizes of anions) 3 1(a)(ii) CuCO ⎯⎯→ CuO + CO 1 3 2 1(b)(i) 1 [Ar] ↿⇂ ↿⇂ ↿⇂ ↿⇂ ↿ 1(b)(ii) 1 1(b)(iii) the (3)d and (4)s are close / similar in energy 1 1(c)(i) M1: species with / has two lone pairs of electrons 2 M2: that form dative (covalent) / co-ordinate bond(s) to a (central) transition-element / metal AND atom / ion OR donates electron pair(s) to a (central) transition-element / metal AND atom / ion © Cambridge University Press & Assessment 2025 Page 7 of 17 1(c)(ii) 3 each correct structure = [1] 1(c)(iii) optical AND geometrical / cis-trans 1 1(c)(iv) identification of either cis isomer AND dipoles / polar bonds / partial charges do not cancel 1 OR identification of either cis isomer AND it is asymmetric and has polar bonds 1(d)(i) 1 complex ion in Na Al F Al F 3– 3 6 6 ligand in Na Al F F– 3 6 1(d)(ii) M1: charge passed = 1.5  30  60 OR 2700 (C) 4 M2: n(e–) = 2700 / 96500 OR 2.80  10–2 (mol) M3: n(Al) = 2.80  10-2 ÷ 3 OR 9.33  10–3 (mol) M4: mass (Al) = (27  9.33  10-3) = 0.25 (g) © Cambridge University Press & Assessment 2025 Page 8 of 17

2(a) the (3)d and (4)s sub-shells / orbitals / electrons are close / similar in energy 1 2(b) species or ion formed by a central metal atom/ion AND surrounded by/bonded to (one or more) ligands 1 2(c)(i) NaOH / OH–(aq) AND precipitation / ligand exchange / deprotonation / acid–base 1 2(c)(ii) M1: Fe(H O) (OH) is oxidised (from + 2 to + 3 on standing) 3 2 4 2 M2: Eo of Fe(H O) (OH) is more negative than Eo of O 2 3 3 2 OR Eo = 0.40 – (–0.56) = (+)0.96 V cell M3: 4Fe(H O) (OH) + O → 4Fe(H O) (OH) + 2H O 2 4 2 2 2 3 3 2 2(d) ∆Go = –2  1.67  96 500 = –322 310 J mol–1 2 M1: ∆Go = –nEo F AND n = 2 cell OR –2  1.67  96 500 M2: ∆Go = –322.3 kJ mol–1 © Cambridge University Press & Assessment 2025 Page 8 of 19

5(a) 1 5(b) • five 3d orbitals (lines, boxes) in the isolated Cu2+ ion of the same energy 2 • splitting: three higher and two lower d orbitals • energy of all five d orbitals in complex higher than all d orbitals in isolated ion any two [1], all three [2] 5(c) M1: more than one (stable) oxidation state / exist in variable oxidation states 2 M2: vacant / empty (d) orbitals are energetically accessible OR vacant / empty (d) orbitals can form dative bonds with ligands 5(d) 2 each row [1] © Cambridge University Press & Assessment 2025 Page 11 of 19 5(e) M1: 2 M2: (shape) square planar AND (bond angle) 180o 5(f)(i) M1: moles MnO – = 0.075  0.0225 = 1.6875  10–3 3 4 M2: moles V2+ = 5 / 3  1.6875  10–3 = 2.8125  10–3 M3: mass V = 50.9  2.8125  10–3 = 0.143 g % of V = 0.143 / 0.250  100 = 57.3 min 2sf 5(f)(ii) 2VO – + 3Zn + 12H+ → 2V2+ + 3Zn2+ + 6H O 2 3 2 M1: 2 : 3 ratio on both sides M2: rest of the equation correct Question Answer Marks

6(a)(i) Ni(CO) 1 4 6(a)(ii) • ethanedioate given as C O 2 2 4 • formula shows one Ni and three ligands • charge = 4– any two [1], all three [2] Ni(C O ) 4– scores [2] 2 4 3 © Cambridge University Press & Assessment 2025 Page 10 of 15 6(a)(iii) F AND optical 1 6(b)(i) N atom can donate one lone pair of electrons 1 6(b)(ii) [Cd(en) ]2+ AND has a larger K / is more stable 1 2 stab 6(b)(iii) [[Cd(CH3NH2)4]2+] 1 [Cd2+][CH3NH2]4 Question Answer Marks

2(a) the (3)d and (4)s sub-shells / orbitals / electrons are close / similar in energy 1 2(b) species or ion formed by a central metal atom/ion AND surrounded by/bonded to (one or more) ligands 1 2(c)(i) NaOH / OH–(aq) AND precipitation / ligand exchange / deprotonation / acid–base 1 2(c)(ii) M1: Fe(H O) (OH) is oxidised (from + 2 to + 3 on standing) 3 2 4 2 M2: Eo of Fe(H O) (OH) is more negative than Eo of O 2 3 3 2 OR Eo = 0.40 – (–0.56) = (+)0.96 V cell M3: 4Fe(H O) (OH) + O → 4Fe(H O) (OH) + 2H O 2 4 2 2 2 3 3 2 2(d) ∆Go = –2  1.67  96 500 = –322 310 J mol–1 2 M1: ∆Go = –nEo F AND n = 2 cell OR –2  1.67  96 500 M2: ∆Go = –322.3 kJ mol–1 © Cambridge University Press & Assessment 2025 Page 8 of 19

5(a) 1 5(b) • five 3d orbitals (lines, boxes) in the isolated Cu2+ ion of the same energy 2 • splitting: three higher and two lower d orbitals • energy of all five d orbitals in complex higher than all d orbitals in isolated ion any two [1], all three [2] 5(c) M1: more than one (stable) oxidation state / exist in variable oxidation states 2 M2: vacant / empty (d) orbitals are energetically accessible OR vacant / empty (d) orbitals can form dative bonds with ligands 5(d) 2 each row [1] © Cambridge University Press & Assessment 2025 Page 11 of 19 5(e) M1: 2 M2: (shape) square planar AND (bond angle) 180o 5(f)(i) M1: moles MnO – = 0.075  0.0225 = 1.6875  10–3 3 4 M2: moles V2+ = 5 / 3  1.6875  10–3 = 2.8125  10–3 M3: mass V = 50.9  2.8125  10–3 = 0.143 g % of V = 0.143 / 0.250  100 = 57.3 min 2sf 5(f)(ii) 2VO – + 3Zn + 12H+ → 2V2+ + 3Zn2+ + 6H O 2 3 2 M1: 2 : 3 ratio on both sides M2: rest of the equation correct Question Answer Marks

1(a) forms (one or more) stable ions / compounds / oxidation states 1 with incomplete / partially filled (3)d orbital(s) / d shell / d sub-shell 1(b)(i) (orbitals) are at the same energy 1 1(b)(ii) (1s2) 2s2 2p6 3s2 3p6 3d9 1 1(c)(i) [Cu(NH ) (H O) ]2+(aq) deep / dark / royal blue 1 3 4 2 2 AND [CuCl ]2–(aq) yellow 4 1(c)(ii) M1: d orbital(s) of different energy / d-d splitting occurs / d sub-shell splits 3 M2: electron(s) promoted / excited M3: light / wavelength / frequency / photon absorbed AND complementary colour seen 1(d)(i) M1: ligand exchange / replacement / substitution / displacement 2 M2: [CuCl4 ]2– + 4NH 3 + 2H 2 O → [Cu(NH 3 ) 4 (H 2 O) 2 ]2+ + 4Cl– 1(d)(ii) M1: one correct 3D structure of [Cu(H O) (NH ) ]2+ 2 2 2 3 4 M2: correct 3D stereoisomer structure of isomer 1 1(d)(iii) cis isomer AND dipoles do not cancel 1 1(e)(i) (two) oxygen and (one) nitrogen (can donate) three lone pair(s) of electrons (to the metal ion) 1 © Cambridge University Press & Assessment 2025 Page 7 of 16 1(e)(ii) [Co(C H NO ) ]– 1 4 5 4 2 1(f)(i) equilibrium constant for the formation of the complex (ion) 1 in a solvent / water / solution OR from its constituent ions or molecules 1(f)(ii) [Ag(CN) ]–(aq) AND largest (value of) K 1 2 stab 1(g) M1 M2: any two [1], all four [2] 3 • moles MnO – = 0.015 ×18.70/1000 = 2.805 × 10–4 4 • moles SO 2– = 2.805 × 10–4 × 5/2 = 7.0125 × 10–4 (in 10 cm3) 3 • moles SO 2– = 1.753 × 10–2 (in 250 cm3) 3 • mass Na SO = 1.753 × 10–2 × 126.1 = 2.21 g 2 3 M3: % purity = 100 × 2.21 / 3.75 = 58.9 – 59.0 % min 2sf Question Answer Marks

2(a)(i) M1: moles of manganate = 23.80 / 1000  0.0500 OR 1.19  10–3 mol 3 OR initial moles of Fe2+ = 17.70 ÷ 277.9 OR 6.37  10–2 mol M2: moles of Fe2+ in aliquot = 5  1.19  10–3 OR 5.95  10–3 mol AND total moles of Fe2+ = 5.95  10–3  10 OR 5.95  10–2 mol OR mass of FeSO ·7H O left = 5.95  10–3  277.9 OR 1.6535 g (in 25 cm3) 4 2 M3: mass of FeSO ·7H O left = 1.6535 g  10 = 16.535 g (in 250 cm3) 4 2 OR mass of FeSO ·7H O left = 277.9  5.95  10–2 = 16.535 g 4 2 percentage oxidised = 100%  (17.70 – 16.535) / 17.70 = 100%  1.165 / 17.70 = 6.58 % min 2sf 2(a)(ii) MnO – / manganate is a (self-)indicator 1 4 OR MnO – / manganate changes colour / purple to colourless / decolourises 4 OR solution changes (from colourless) to pink / purple at the end-point 2(b)(i) 1 2(c) manganese is both oxidised and reduced (to a single oxidation state) 2 from +VII / +7 to +III / +3 AND +II / +2 to +III / +3 2(d)(i) K = [Mn2+] [OH–]2 1 sp © Cambridge University Press & Assessment 2026 Page 10 of 18 2(d)(ii) [Mn2+(aq)] = 3.20  10–3 / 88.9 OR 3.60  10–5 mol dm–3 3 K = 3.60  10–5  (2  3.60  10–5)2 = 4  (3.60  10–5)3 sp = 1.87  10–13 min 2sf mol3 dm–9 2(e)(i) M1: d orbital(s) of two different energies / d-d splitting occurs 3 OR d orbital(s)/d (sub)-shell splits / d-d gap M2: electron(s) promoted / excited OR electron(s) moves to higher (d–) orbital M3: wavelength / frequency / light / photon / h / hf absorbed OR radiation / energy from visible (region) absorbed AND colour (seen) is complementary OR wavelength / frequency / colour / light not absorbed is transmitted / reflected / seen © Cambridge University Press & Assessment 2026 Page 11 of 18 2(e)(ii) 4 formula [Mn(C O ) ]3– 2 4 3 formula of C O 2– ligand 2 4 shape octahedral coordination 6 number type of optical stereoisomerism structures and Question Answer Marks

5(a) similarity in energy of (3)d and (4)s (subshells / orbitals) 1 this is a syllabus statement – do not allow A same much variation of meaning, I statements that can be understood to refer to 3d only. 5(b) 3d7 4s2 / 4s2 3d7 1 A full configurations with no errors. 3d7 / 3d7 4s0 5(c) M1 the d orbitals 3 are split / become non-degenerate / reference to E within d-subshell or E between d orbitals M2 electrons are promoted / excited / jump to higher level owtte M3 absorbing (energy of) light / photon / frequency / wavelength / h and ‘complementary’ may be described but complementary colour is seen / reflected / transmitted ‘different colour’ is not enough. M3 CON emits / energy released. 5(d) M1 blue to red / blue to pink 2 A named shades of blue and pink. M2 CoCl + 6H O → [Co(H O) ]2+ + 2Cl – or 2 2 2 6 CoCl 2– + 6H O → [Co(H O) ]2+ + 4Cl – I CoCl + 6H O → CoCl 6H O . 4 2 2 6 2 2 2 2 I Co2+ + 6H O → [Co(H O) ]2+. 2 2 6 5(e)(i) (white / brown / off white) precipitate / ppt / solid and 1 CON clearly wrong colours, e.g. brown (solution) black / blue / green / purple or wrong observations, e.g. fizzing. 5(e)(ii) starch and 1 blue / black to colourless / white / off-white colourless / white to blue / black is CON. 5(e)(iii) redox 1 A oxidation-reduction (both needed). © Cambridge University Press & Assessment 2026 Page 12 of 21 Trace ID: PC-F9EA0E463D Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. Licensed for hosting on papacambridge.com only. P97a01p/4a1 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/41 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 5(e)(iv) • moles of S O 2– = 0.2  37.6 / 1000 = 7.52  10–3 3 ⚫✓✓✓ two points for one mark 2 3 • moles of I = 3.76  10–3 ecf 2 • moles of Cu = 7.52  10–3 ecf correct answer scores [3]. • mass of Cu = 0.48 / 0.478 / 0.4775 / 0.47752 g ecf 0.239 g, 0.955 g or 1.41 g on the answer line, without any correct, understandable working, scores [0] Question Answer Marks Guidance

6(a) M1 two lone pairs / LP 2 M2 donated / form dative bond(s) / coordinate bond(s) CON ‘2 or more dative bonds’. to (central) metal / TM / TE atom / ion 6(b)(i) [Fe(C 2 O 4 ) 3 ]3– or Fe(C 2 O 4 ) 3 3– 1 6(b)(ii) M1 One correct isomer of [Fe(C 2 O 4 ) 3 ]3– drawn with 3D and oct 2 Correct 3D. octahedral, different These two renditions of octahedral are M2 Two optical isomers drawn with 3D and octahedral only acceptable. I charges. 6(b)(iii) optical only 1 © Cambridge University Press & Assessment 2026 Page 13 of 21 Trace ID: PC-F9EA0E463D Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. Licensed for hosting on papacambridge.com only. P97a01p/4a1 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/41 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 6(c) © Cambridge University Press & Assessment 2026 Page 14 of 21   H  H g g 2 + I 4  2   I  − −   4 2 A [HgI 2–]. 4 M1 A [Hg2+] with complexing H 2 O. The charges shown here are essential. Final set of brackets must be square 3. Penalise two or more round outer brackets. M2 mol–4 dm12 unc ecf only after K with 4th power. stab Question Answer Marks Guidance

1(a)(i) • they behave as catalysts 1 I high melting point / high densities. I form complex ions. • (they form) coloured compounds / complexes / ions I variable / multiple oxidation states. BOTH [1] 1(a)(ii) the d and s sub-shells / orbitals are close / similar in energy 1 I use of ‘shells’ for orbitals. A (n-1)d and ns if any numbers see.n A electrons in d and s sub-shells / orbitals available for bonding 1(b)(i) 1 A use of . 1(b)(ii) dative (covalent) / coordinate 1 1(c) vacant (d) orbital(s) are energetically accessible 1 I subshells / shells / energy levels. or vacant (d) orbital(s) can form dative bonds with ligands I partially filled d-orbital(s) are energy or vacant (d) orbital(s) can accept a (lone) pair of electrons to form a accessible. dative bond A ‘empty’ / ‘unoccupied’ for vacant. 1(d)(i) NaOH / OH– 1 A NH for NaOH. 3 and precipitation / ligand exchange / A ligand substitution / ligand. / neutralisation / deprotonation / acid-base BOTH replacement / ligand displacement. I precipitate. 1(d)(ii) M1 [Cr(H O) (OH) ] + 6NH → [Cr(NH ) ]3+ + 3H O + 3OH– 2 A use [Cr(NH ) ](OH) as a product. 2 3 3 3 3 6 2 3 6 3 M2 ligand exchange / replacement / substitution / displacement © Cambridge University Press & Assessment 2026 Page 7 of 25 Trace ID: PC-9D76E91B48 Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. Licensed for hosting on papacambridge.com only. P97a01p/4a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/42 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(e) M1 one correct 3D structure of [Cr(H O) (OH) ] 2 CON use of O H once only then apply ecf. 2 3 3 2 M2 correct 3D structure of the other isomer One isomer - two water & two OH ligands at 180°. One isomer – all water & all OH ligands at 90°. 1(f)(i) M1 [Fe(H O) ]3+ / Fe3+ weakens O–H bonds / polarises O–H bonds 2 A M1 [Fe(H O) ]3+ undergoes 2 6 2 6 hydrolysis / deprotonation. M2 [Fe(H O) ]3+ → [Fe(H O) OH]2+ + H+ A M1 one of the H O ligands loses a H+. 2 6 2 5 2 A M1 H O in the complex can donate a H+. 2 A other alternatives for M2 for example [Fe(H O) ]3+ + H O → [Fe(H O) OH]2+ + 2 6 2 2 5 H O+ . 3 1(f)(ii) Fe3+ has lower pH / Fe2+ has a higher pH 1 A Fe3+ is more acidic / Fe2+ is less acidic and for ‘lower pH / higher pH”. Fe3+ has a higher charge / smaller radii / higher charge density (so easier to hydrolyse) BOTH ora 1(g) M1 (Ag+) d-subshell is full / complete or d10 or d-orbitals are full 2 A use of 3d instead of 4d. I d orbital is full for M1. I M1 no empty d subshells. M2 no d-d(*) transition or no d electrons promoted / excited [1] CON M2 no d-d splitting / no E gap. or cannot absorb light in the visible spectrum A M2 cannot absorb energy in the visible spectrum. (must imply promotion) ‘d’ can be qualified from M1 for M2 © Cambridge University Press & Assessment 2026 Page 8 of 25 Trace ID: PC-9D76E91B48 Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. Licensed for hosting on papacambridge.com only. P97a01p/4a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/42 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(h) M1 M2 5 A route 1 via 500 cm3 in M3 & M4 • moles MnO – = 0.025  0.02180 = 5.45  10–4 moles C O 2– = 1.3625  10–3  20 = 0.02725 4 2 4 • moles C O 2– = 2.5  5.45  10–4 = 1.3625  10–3 moles H C O = 1.02  10–3  20 = 0.0204 2 4 2 2 4 ecf (moles MnO –  2.5) moles Na C O = 0.02725 – 0.0204 = 0.00685. 4 2 2 4 • moles OH– = 0.150  0.0136 = 2.04  10–3 • moles H 2 C 2 O 4 = ½  2.04  10–3 = 1.02  10–3 mass Na 2 C 2 O 4 = 0.00685  134 = 0.9179 g ecf (moles OH– x ½) any two [1] all four [2] A route 2 in M4 & M3 moles C O 2– = 1.3625  10–3  20 = 0.02725 2 4 M3 moles Na C O = 1.3625  10–3 – 1.02  10–3 = 3.425  10–4 ecf moles H C O = 1.02  10–3  20 = 0.0204 2 2 4 2 2 4 (in 25 cm3 A) [1] mass C O 2– = 0.02725  134 = 3.6515 g 2 4 moles H C O = 0.0204  134 = 2.7336 g. 2 2 4 M4 moles Na C O = 3.425  10–4  20 = 6.85  10–3 ecf 2 2 4 (in 500 cm3 A) (M3) mass Na C O = 3.6515 – 2.7336 = 2 2 4 mass Na C O = 6.85  10–3  134 = 0.9179 g [1] 0.9179 g. 2 2 4 M5 % = 0.9179 / 5.00  100 = 18.4 / 18.358 [1] min 2sf ecf A ecf M4 answer to calculated value  20  correct answer scores [5] 134. A 18.2(24) (from use of 3sf 1.36  10–3) for correct answer A ecf M5 for (a calculated mass ÷ 5.0)  100. © Cambridge University Press & Assessment 2026 Page 9 of 25 Trace ID: PC-9D76E91B48 Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. Licensed for hosting on papacambridge.com only. P97a01p/4a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/42 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/

5(a) similarity in energy of (3)d and (4)s (subshells / orbitals) 1 this is a syllabus statement – do not allow A same much variation of meaning, I statements that can be understood to refer to 3d only. 5(b) 3d7 4s2 / 4s2 3d7 1 A full configurations with no errors. 3d7 / 3d7 4s0 5(c) M1 the d orbitals 3 are split / become non-degenerate / reference to E within d-subshell or E between d orbitals M2 electrons are promoted / excited / jump to higher level owtte M3 absorbing (energy of) light / photon / frequency / wavelength / h and ‘complementary’ may be described but complementary colour is seen / reflected / transmitted ‘different colour’ is not enough. M3 CON emits / energy released. 5(d) M1 blue to red / blue to pink 2 A named shades of blue and pink. M2 CoCl + 6H O → [Co(H O) ]2+ + 2Cl – or 2 2 2 6 CoCl 2– + 6H O → [Co(H O) ]2+ + 4Cl – I CoCl + 6H O → CoCl 6H O . 4 2 2 6 2 2 2 2 I Co2+ + 6H O → [Co(H O) ]2+. 2 2 6 5(e)(i) (white / brown / off white) precipitate / ppt / solid and 1 CON clearly wrong colours, e.g. brown (solution) black / blue / green / purple or wrong observations, e.g. fizzing. 5(e)(ii) starch and 1 blue / black to colourless / white / off-white colourless / white to blue / black is CON. 5(e)(iii) redox 1 A oxidation-reduction (both needed). © Cambridge University Press & Assessment 2026 Page 12 of 21 Trace ID: PC-F2CDA313A1 Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. Licensed for hosting on papacambridge.com only. P97a01p/4a3 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/43 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 5(e)(iv) • moles of S O 2– = 0.2  37.6 / 1000 = 7.52  10–3 3 ⚫✓✓✓ two points for one mark 2 3 • moles of I = 3.76  10–3 ecf 2 • moles of Cu = 7.52  10–3 ecf correct answer scores [3]. • mass of Cu = 0.48 / 0.478 / 0.4775 / 0.47752 g ecf 0.239 g, 0.955 g or 1.41 g on the answer line, without any correct, understandable working, scores [0] Question Answer Marks Guidance

6(a) M1 two lone pairs / LP 2 M2 donated / form dative bond(s) / coordinate bond(s) CON ‘2 or more dative bonds’. to (central) metal / TM / TE atom / ion 6(b)(i) [Fe(C 2 O 4 ) 3 ]3– or Fe(C 2 O 4 ) 3 3– 1 6(b)(ii) M1 One correct isomer of [Fe(C 2 O 4 ) 3 ]3– drawn with 3D and oct 2 Correct 3D. octahedral, different These two renditions of octahedral are M2 Two optical isomers drawn with 3D and octahedral only acceptable. I charges. 6(b)(iii) optical only 1 © Cambridge University Press & Assessment 2026 Page 13 of 21 Trace ID: PC-F2CDA313A1 Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. Licensed for hosting on papacambridge.com only. P97a01p/4a3 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/43 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 6(c) © Cambridge University Press & Assessment 2026 Page 14 of 21   H  H g g 2 + I 4  2   I  − −   4 2 A [HgI 2–]. 4 M1 A [Hg2+] with complexing H 2 O. The charges shown here are essential. Final set of brackets must be square 3. Penalise two or more round outer brackets. M2 mol–4 dm12 unc ecf only after K with 4th power. stab Question Answer Marks Guidance

6(a) (ion formed from a central) metal atom / ion 1 A transition element for metal. (surrounded by, or bonded to, one or more) ligands 6(b)(i) M1 x = 1, y = 5 2 A negative or positive signs. M2 x = 4, y = 2 6(b)(ii) 6 / six 1 Only answer. 6(b)(iii) 2 No mark for either diagram with wrong 3D. M1 one diagram with No mark for diagrams with bidentate correct 3D and ligands. formula I incorrect ligand attachment (i.e. though the H of NH 3 ). M2 Penalise incorrect monodentate ligands once only, then A. second diagram shows correct 3D One diagram must have all NH 3 ligands and other isomer cis, one diagram must have two NH 3 ligands trans i.e one facial, one meridial. 6(b)(iv) yes no 1 A crosses as ticks if other box on row is stereoisomerism ✓ blank. optical isomerism ✓ geometric isomerism ✓ Three ticks only, all correct. 6(c)(i) equilibrium constant 1 I ‘the ratio of…’. They have been given the formation of a complex expression and are just describing it. in a solvent / water / from its (constituent) ions / molecules I ‘in a solution’ for solvent. 6(c)(ii) mol–6 dm18 any order 1 Only answer. © Cambridge University Press & Assessment 2026 Page 15 of 21 Trace ID: PC-0F078E40FE Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. Licensed for hosting on papacambridge.com only. P97a01p/4a4 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/44 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 6(c)(iii) M1 working makes it clear all terms substituted into the expression correctly © Cambridge University Press & Assessment 2026 Page 16 of 21 4 . 8 0  1 0 7 = ( 0 . 4 5 5 ) 6 0  .  0  7 N 6 i 2 ( H 2 O ) 6  2 +  ,   N i ( H 2 O ) 6  2 +  = ( 0 . 4 5 5 0 ) . 6 0  7 4 6 . 2 8 0  1 0 7 2 only ecf is M2 for TE errors in the concentrations / K . stab Correct answer scores [2] M2 1.8 / 1.79  10–7 min 2sf 6(c)(iv) [Ni(H O) ]2+ + 6 NH → (1) [Ni(NH ) ]2+ + 6 H O 1 Only answer. 2 6 3 3 6 2 6(c)(v) Ligand exchange / displacement / replacement / substitution 1 Question Answer Marks Guidance