Group 2

1(a) Co2+ = [Ar] 3d7 (4s0) 1 Co3+ = [Ar] 3d6 (4s0) 1(b) M1/2: Any two of: 3 • Co3+ is reduced Co2+ • oxygen gas/O is evolved 2 • E of Co3+ greater than E of O 2 M3: no change (to [Co(edta)]–) / not feasible OWTTE 1(c) Any two of VISUAL observations: 2 • condensation on tube / steam evolved • brown fumes / brown gas evolved • O formed that relights a glowing splint 2 • (solid) dissolves / turns to liquid 1(d) M1: cationic radius / ion size increases (down the group) 2 M2: less polarisation / distortion of nitrate ion / anion / NO – 3 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 / hydroxide ion / hydroxide group / OH– / OH 1(b)(i) Ca(OH) (s) ⇌ Ca2+(aq) + 2OH–(aq) 1 2 1(b)(ii) M1: 2 K = [Ca2+][OH–]2 sp OR K = 4x3 sp M2: x = 3√5.02 × 10–6 / 4 = 0.0108 / 0.011 / 1.08 × 10–2 / 1.1 × 10–2 (mol dm–3) min 2 sf 1(b)(iii) less soluble / decreases due to the common ion effect 1 OR decreases as equilibrium in (b)(i) has shifted to the left OR decreases as [OH–] increases causing [Ca2+][OH–](2) to exceed its K sp © UCLES 2021 Page 5 of 17

2(a) M1: increases down the group 3 M2: radius / size of cation / M2+ increases OR charge density of cation / M2+ decreases M3: less polarisation / less distortion of anion / NO – ion OR less weakening of NO bond 3 2(b)(i) Pb(NO )  PbO + 2NO + ½O 1 3 2 2 2 2(b)(ii) lead nitrate / Pb(NO ) would decompose more / easier 1 3 2 AND as Pb2+ is smaller / Pb2+ has larger charge density (so more polarising) 2(c)(i) BaC O  BaO + CO + CO OR BaC O  BaO + 2CO + ½O 1 2 4 2 2 4 2 2(c)(ii) M1: [a] initial moles MnO – = 0.0200 × 0.050 = 1.00 × 10–3 4 4 [b] moles Fe2+ = 0.050 × 0.0304 = 1.52 × 10–3 M2: [a] moles MnO – unreacted = 1.52 × 10–3 / 5 = 3.04 × 10–4 4 [b] moles MnO – reacted = 1.00 × 10–3 – 3.04 × 10–4 = 6.96 × 10–4 4 M3: moles C O 2- reacted = 6.96 × 10–4 × 5/2 = 1.74 × 10–3 2 4 M4: mass of BaC O = 225.3 × 1.74 × 10–3 = 0.392 g 2 4 % Purity of BaC O = 100 × 0.392/0.50 = 78.4 2 4 2(d) M1: [OH–] = 2 × 0.12 = 0.24 (mol dm–3) 2 [H+] = 1 × 10–14/0.24 = 4.17 × 10–14 / pOH = –log(0.24) OR 0.62 M2: pH = –log[H+] = 13.4 OR pH = 14 – 0.6 = 13.4 © UCLES 2021 Page 6 of 16

1(a) M1: increases down the group 3 M2: radius / size of (cat)ion / M2+ increases M3: less polarisation / distortion of anion / hydroxide ion / hydroxide group / OH– / OH 1(b)(i) Ca(OH) (s) ⇌ Ca2+(aq) + 2OH–(aq) 1 2 1(b)(ii) M1: 2 K = [Ca2+][OH–]2 sp OR K = 4x3 sp M2: x = 3√5.02 × 10–6 / 4 = 0.0108 / 0.011 / 1.08 × 10–2 / 1.1 × 10–2 (mol dm–3) min 2 sf 1(b)(iii) less soluble / decreases due to the common ion effect 1 OR decreases as equilibrium in (b)(i) has shifted to the left OR decreases as [OH–] increases causing [Ca2+][OH–](2) to exceed its K sp © UCLES 2021 Page 5 of 17

4(a) • barium carbonate / Ba / BaCO 2 3 • larger ionic radius OR smaller charge density of cation / M2+ [1] • anion / CO 2– / carbonate ion is less distorted / less polarised OR C-O / C=O less weakened [1] 3 4(b) • calcium oxide / calcium hydroxide 3 • CaSO / calcium sulfate is more soluble OR BaSO is less soluble [1] 4 4 • ΔH and ΔH are less exothermic / more endothermic (for BaSO ) [1] latt hyd 4 • ΔH is dominant factor / ΔH change is greater OR ΔH changes less [1] hyd hyd latt 4(c)(i) mass of CO = 0.02 × 44 = 0.88 g [1] 1 2 4(c)(ii) (writes correct equation, deduces 3 CO per mole) 2 2 moles of propane = 0.02 / 3 OR 0.00667 OR 1 / 150 [1] mass of propane = 0.02 / 3 × 44 = 0.293 g [1] ecf M1 × 44 3sf needed Question Answer Marks

4(a) strontium nitrate AND because of larger cationic radius [1] 2 NO – / nitrate ion / anion is less distorted / polarised 3 OR N–O or N=O bond less weakened / distorted [1] 4(b) M1 magnesium oxide requires more water to dissolve AND because Sr(OH) is more soluble [1] 3 2 M2 lattice and hydration energies less for Sr(OH) [1] 2 M3 lattice energy is dominant factor / change in lattice energy is greater [1] 4(c)(i) 0.13 [1] 1 4(c)(ii) 26.7 cm3 must be 3SF [1] 1 © UCLES 2021 Page 7 of 12

4(a) • barium carbonate / Ba / BaCO 2 3 • larger ionic radius OR smaller charge density of cation / M2+ [1] • anion / CO 2– / carbonate ion is less distorted / less polarised OR C-O / C=O less weakened [1] 3 4(b) • calcium oxide / calcium hydroxide 3 • CaSO / calcium sulfate is more soluble OR BaSO is less soluble [1] 4 4 • ΔH and ΔH are less exothermic / more endothermic (for BaSO ) [1] latt hyd 4 • ΔH is dominant factor / ΔH change is greater OR ΔH changes less [1] hyd hyd latt 4(c)(i) mass of CO = 0.02 × 44 = 0.88 g [1] 1 2 4(c)(ii) (writes correct equation, deduces 3 CO per mole) 2 2 moles of propane = 0.02 / 3 OR 0.00667 OR 1 / 150 [1] mass of propane = 0.02 / 3 × 44 = 0.293 g [1] ecf M1 × 44 3sf needed Question Answer Marks

1(a)(i) 1 ARROW 1 starts from O– to the C–O bond AND ARROW 2 starts at the C-O bond to other O– ion 1(a)(ii) M1 increases (down the group) 3 M2 (cat)ionic radius / ion size increases (down the group) OR charge density of M2+ decreases M3 less polarisation / distortion of anion / carbonate ion / CO (2)– 3 1(b)(i) M1 energy released when one mole of a ionic solid / compound is formed 2 M2 from gas (phase) ion(s) / gaseous ion(s) (under standard conditions) 1(b)(ii)  (H / it) becomes more positive/less negative 2 decomp (down the group)  size /(ionic) radii of oxide ion is smaller (than carbonate ion) ORA  so H of oxides becomes ORA latt less exothermic faster OR less negative faster OR changes more OR changes faster Any two [1], all three [2] 1(c)(i) 2MnO – + 6H+ + 5SO 2–  2Mn2+ + 3H O + 5SO 2– 1 4 3 2 4 © UCLES 2023 Page 6 of 19 1(c)(ii) M1 M2 3 any two bullets [1] or all four [2]  moles MnO – = 0.025  22.40 / 1000 = 5.6  10–4 4  moles SO 2– = 5.6  10–4  5 / 2 = 1.4  10–3 (in 25 cm3) ecf from (c)(i) and bullet 1 3  moles SO 2– = 1.4  10–2 (in 250 cm3) ecf bullet 2 3  mass K SO = 1.4  10–2  158.3 = 2.2162 g ecf bullet 3 2 3 OR moles K SO (if 100% pure) = 3.40 ÷ 158.3 = 0.02148 2 3 M3 % purity = 100  2.2162 / 3.40 = 65.2 / 65.3 % ecf min 2sf OR % purity = 100  0.014 / 0.02148 = 65.2 / 65.3 % 1(d) S() tetrahedral 1 Question Answer Marks

4(a)(i) • Co(OH) OR Co(OH) (H O) 2 2 2 2 4 • [Co(NH ) ]2+ OR [Co(NH ) ]3+ 3 6 3 6 • [CoCl ]2– 4 any two [1] all three [2] 4(a)(ii) pink to 1 blue [1] 4(b)(i) 2Ca(NO ) → 2CaO + 4NO + O 1 3 2 2 2 OR Ca(NO ) → CaO + 2NO + ½O [1] 3 2 2 2 © UCLES 2023 Page 9 of 18 4(b)(ii) M1: Mg(NO ) below 480 °C, 3 3 2 Ba(NO ) above 520 °C BOTH [1] u / c 3 2 M2: ionic radii of M2+ increases down the group OR radii of Ba2+ is greater (than Mg2+) OR charge density of M2+ decreases down the group OR charge density of Ba2+ is smaller (than Mg2+) [1] ORA u / c M3: (larger cations) polarise / distort anion / NO – less 3 OR (larger ions) weaken N-O / N=O (bond) less [1] ORA Question Answer Marks

5(a) MgC O → MgO + CO + CO [1] 1 2 4 2 © UCLES 2023 Page 7 of 14 5(b) magnesium ethanedioate decomposes at lower T because Mg2+ has smaller radius than Ca2+ [1] 2 so anion is more polarised by Mg2+ [1] 5(c) (27.05 ÷ 1000)  0.02 = 5.41  10–5 moles MnO – [1] 3 4 5.41  10–5  5/2 = 1.3525  10–4 moles C O 2– [1] 2 4 0.00338 mol dm–3 [1] Question Answer Marks

4(a)(i) • Co(OH) OR Co(OH) (H O) 2 2 2 2 4 • [Co(NH ) ]2+ OR [Co(NH ) ]3+ 3 6 3 6 • [CoCl ]2– 4 any two [1] all three [2] 4(a)(ii) pink to 1 blue [1] 4(b)(i) 2Ca(NO ) → 2CaO + 4NO + O 1 3 2 2 2 OR Ca(NO ) → CaO + 2NO + ½O [1] 3 2 2 2 © UCLES 2023 Page 9 of 18 4(b)(ii) M1: Mg(NO ) below 480 °C, 3 3 2 Ba(NO ) above 520 °C BOTH [1] u / c 3 2 M2: ionic radii of M2+ increases down the group OR radii of Ba2+ is greater (than Mg2+) OR charge density of M2+ decreases down the group OR charge density of Ba2+ is smaller (than Mg2+) [1] ORA u / c M3: (larger cations) polarise / distort anion / NO – less 3 OR (larger ions) weaken N-O / N=O (bond) less [1] ORA Question Answer Marks

1(a)(i) M1 strontium > calcium > magnesium 4 M2H and H both become less exothermic / less negative latt hyd M3H changes more latt M4H becomes more exothermic / more negative sol 1(a)(ii) pH increases as the concentration of [OH–] ions increases 1 1(b) M1 [H+] = 10–12.2 OR 6.31  10–13 4 M2 [OH–] = 0.0158 mol dm–3 ecf M3 [Ba(OH) ] = 0.01585 ÷ 2 = 7.92 ecf 2 M4 mol of Ba(OH) = 0.00792 ÷ 4 = 1.98  10–3 2 mass Ba(OH) = 0.339 g ecf 2 1(c)(i) K = [Fe2+][OH–]2 1 sp 1(c)(ii) M1 K = 4  (5.85  10–6)3 = 8.01  10–16 2 sp M2 mol3 dm–9 Question Answer Marks

1(a)(i) M1 strontium > calcium > magnesium 4 M2H and H both become less exothermic / less negative latt hyd M3H changes more latt M4H becomes more exothermic / more negative sol 1(a)(ii) pH increases as the concentration of [OH–] ions increases 1 1(b) M1 [H+] = 10–12.2 OR 6.31  10–13 4 M2 [OH–] = 0.0158 mol dm–3 ecf M3 [Ba(OH) ] = 0.01585 ÷ 2 = 7.92 ecf 2 M4 mol of Ba(OH) = 0.00792 ÷ 4 = 1.98  10–3 2 mass Ba(OH) = 0.339 g ecf 2 1(c)(i) K = [Fe2+][OH–]2 1 sp 1(c)(ii) M1 K = 4  (5.85  10–6)3 = 8.01  10–16 2 sp M2 mol3 dm–9 Question Answer Marks

1(a) CaCO → CaO + CO [1] 1 3 2 1(b) M1: calcium carbonate AND calcium ion / Ca2+ smaller / ionic radius bigger down group 2 M2: carbonate ion / anion / CO 2– is more distorted/polarised by Ca2+ 3 1(c)(i) calcium hydroxide / Ca(OH) 1 2 1(c)(ii) M1: A / calcium hydroxide has more exothermic H AND H than B / barium hydroxide 3 latt hyd M2: difference in H is greater for A / calcium hydroxide than for B / barium hydroxide latt M3: H is less exothermic for A / calcium hydroxide than for B / barium hydroxide sol Question Answer Marks

1(a)(i) Ca(NO ) → CaO + 2NO + ½O [1] 1 3 2 2 2 1(a)(ii) M1: temperature increases down the group 3 M2: ionic radius OR size of cation / M(2)+ AND increases M3: less polarisation / less distortion AND of anion / nitrate ion OR less weakening of NO bond / harder to break NO bond 1(b) M1: moles of SrO = 0.333  103.6 = 3.214  10-3 AND moles of Sr(OH) = 3.214  10-3 OR 9 / 2800 4 2 M2: moles of OH– in 250 cm3 = 3.214  10-3  2 = 6.429  10-3 AND moles of OH– in 1 dm3 = 6.429  10-3  4 = 0.0257 M3: [H+] = 1.00  10–14  0.0257 = 3.89  10–13 OR pOH = –log[OH–] = 1.59 M4: pH = –log(3.89  10–13) = 12.41 must be to 2dp OR pH = 14 –1.59 = 12.41 must be 2 dp

1(a) CaCO → CaO + CO [1] 1 3 2 1(b) M1: calcium carbonate AND calcium ion / Ca2+ smaller / ionic radius bigger down group 2 M2: carbonate ion / anion / CO 2– is more distorted/polarised by Ca2+ 3 1(c)(i) calcium hydroxide / Ca(OH) 1 2 1(c)(ii) M1: A / calcium hydroxide has more exothermic H AND H than B / barium hydroxide 3 latt hyd M2: difference in H is greater for A / calcium hydroxide than for B / barium hydroxide latt M3: H is less exothermic for A / calcium hydroxide than for B / barium hydroxide sol Question Answer Marks

1(a)(i) Sr(HCO ) → SrCO + CO + H O 1 3 2 3 2 2 1(a)(ii) M1: radius of cation / M2+ increases OR charge density of cation / M2+ decreases 2 M2: less polarisation / less distortion of the anion / carbonate ion 1(b) M1: least soluble CaF < SrF < BaF most soluble 4 2 2 2 M2: H and H both become less exothermic / less negative latt hyd M3: H changes less / becomes less exothermic by a smaller extent hyd OR H changes more / becomes less exothermic by a larger extent latt M4: H becomes more exothermic / more negative sol 1(c)(i) enthalpy change when one mole of gaseous ions dissolve in water to form a solution 1 1(c)(ii) M1: ionic radii AND ionic charge 2 M2: (ionic) radii increase / charge density decreases AND ∆H decreases/less exothermic AND less attraction between hyd water molecules and (gaseous) ions OR as ionic charge increases / charge density increases AND ∆H increases/more exothermic AND more attraction between hyd water molecules and (gaseous) ions 1(d) M1: use of –2957 / –1926 / –505 AND 2  (–505) 2 M2: correct signs and evaluation ∆H of MgF (s) = –1926 + (2  –505) – (–2957) = (+)21 kJ mol–1 sol 2 1(e)(i) M1: K = [Hg 2+] [F–]2 2 sp 2 M2: units = mol3 dm–9 1(e)(ii) K = 22  (9.20  10–3)3 = 3.11  10–6 min 2sf 1 sp © Cambridge University Press & Assessment 2025 Page 7 of 19

1(a) Mg(NO ) → MgO + 2NO + ½O OR 2Mg(NO ) → 2MgO + 4NO + O 1 3 2 2 2 3 2 2 2 1(b) M1: Mg(NO ) / magnesium nitrate 2 3 2 AND magnesium ion / Mg2+ AND is smaller / has higher charge density M2: nitrate ion / anion is more distorted / polarised 1(c)(i) magnesium sulfate and water / MgSO and H O 1 4 2 1(c)(ii) M1: magnesium sulfate / A has a more exothermic H and H 3 latt hyd M2: difference in H is greater hyd M3: magnesium sulfate / A has a more exothermic H sol Question Answer Marks

1(a)(i) Sr(HCO ) → SrCO + CO + H O 1 3 2 3 2 2 1(a)(ii) M1: radius of cation / M2+ increases OR charge density of cation / M2+ decreases 2 M2: less polarisation / less distortion of the anion / carbonate ion 1(b) M1: least soluble CaF < SrF < BaF most soluble 4 2 2 2 M2: H and H both become less exothermic / less negative latt hyd M3: H changes less / becomes less exothermic by a smaller extent hyd OR H changes more / becomes less exothermic by a larger extent latt M4: H becomes more exothermic / more negative sol 1(c)(i) enthalpy change when one mole of gaseous ions dissolve in water to form a solution 1 1(c)(ii) M1: ionic radii AND ionic charge 2 M2: (ionic) radii increase / charge density decreases AND ∆H decreases/less exothermic AND less attraction between hyd water molecules and (gaseous) ions OR as ionic charge increases / charge density increases AND ∆H increases/more exothermic AND more attraction between hyd water molecules and (gaseous) ions 1(d) M1: use of –2957 / –1926 / –505 AND 2  (–505) 2 M2: correct signs and evaluation ∆H of MgF (s) = –1926 + (2  –505) – (–2957) = (+)21 kJ mol–1 sol 2 1(e)(i) M1: K = [Hg 2+] [F–]2 2 sp 2 M2: units = mol3 dm–9 1(e)(ii) K = 22  (9.20  10–3)3 = 3.11  10–6 min 2sf 1 sp © Cambridge University Press & Assessment 2025 Page 7 of 19

2(a) 1 I LP drawn / any charges on diagram. ARROW 1 from O– to C–O bond (arrow can start anywhere on O). or BOTH arrows [1] ARROW 2 from C–O bond to the other O– . 2(b) • PbCO (most) CaCO CuCO (least) 2 A Pb(2+)(most) Ca(2+) Cu(2+) (least). 3 3 3 • (stability increases) as (ionic) radii increases / size of M2+ increases / NO ecf. or Pb2+ largest radii ora Bullets are all u / c. A bullet 2 charge density of M2+ decreases. • less polarisation / distortion of carbonate ion / anion / CO (2)– 3 or less weakening of CO bond / C-O / C=O  ✓ ✓ CON bullet 3 stronger ionic bond linked to larger ionic radii. I C=O is less polarised. I weaker ionic bond. 2(c) M1 H and H (both) become less exothermic / less negative [1] 3 A M1 H and H decrease. latt hyd latt hyd A M1 H and H become more latt hyd endothermic / positive. M2 H changes more / changes faster / dominant factor / becomes less CON missing  or H once only then ecf. hyd exothermic by a larger extent [1] ora M3 H becomes less exothermic / less negative I M3 H decreases. sol sol or H becomes more endothermic / more positive I M3 H becomes less exothermic. sol solubility 2(d)(i) M1 (K for Mg(OH) ) = [Mg2+][OH–]2 [1] 2 sp 2 M2 units mol3 dm–9 [1] ecf from M1 I state symbols. 2(d)(ii) [H+] = 10–10.35 = 4.47  10–11 1 [OH–] = 1  10–14 ÷ 4.47  10–11 = 2.24  10–4 min 2sf © Cambridge University Press & Assessment 2026 Page 10 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/ 2(d)(iii) K = (0.5  2.24  10–4)  (2.24  10–4)2 1 A ecf sp K = 5.61(2) / 5.62  10–12 u / c min 2sf ecf for 2(d)(i) and 2(d)(ii) correct calculated answer of sp K = (0.5  2(d)(ii))  (2(d)(ii))2. sp I units even if incorrect NO ecf from K = [Mg2+][OH–]. sp © Cambridge University Press & Assessment 2026 Page 11 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)(i) Ca(NO ) → CaO + 2NO + 3 2 2 © Cambridge University Press & Assessment 2026 Page 14 of 21 1 2 1 A other multiples. O or 2 I state symbols. 2Ca(NO ) → 2CaO + 4NO + O 3 2 2 2 5(a)(ii) M1 increases / more stable (down the group) and 2 I atomic radius. ionic / M2+ radius increases / charge density of ion / M2+ decreases CON charge density increasing. I nitrate less polarised / distorted. M2 anion / nitrate ion / NO – less polarised / distorted or I less polarisation ‘between’ ions. 3 N=O / N–O less polarised / distorted/weakened A N–O bond stronger / harder to break. A distortion ‘with’ or ‘to’ NO –. 3 A NO 2–. 3 CON M2 for stronger ionic bond / attraction between ions. I ‘nitrate group’ for NO – . 3 5(b)(i) MgSO more soluble than BaSO 1 A MgSO is soluble and BaSO is 4 4 4 4 insoluble. Must explicitly be a comparison of the sulfates A solubility of Gp2 sulfates decreases (down the group). I comparison of basicity. I comparisons between Mg(OH) and 2 Ba(OH) . 2 I all discussion regarding ΔH , etc. latt 5(b)(ii) M1 H and H less negative / exothermic (down group 2) 3 A ora throughout. latt hyd M2 H changes more / is dominant factor / significant A decreases for M1. latt M3 H more exothermic down group A ‘of oxides’ as a slip. sol M3 I ‘solubility more exothermic’. or in terms of the compounds in the question: I HE and LE unless defined. M1 H and H are less negative for Ba(OH) Penalise missing  or H once only. latt hyd 2 M2 H latt is less negative by a larger amount OWTTE I H solubility . I any discussion of sulfates. M3 H is more exothermic for Ba(OH) (than for Mg(OH) ) sol 2 2 I discussion of ionic radii / charge density throughout. 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/