Planning, analysis and evaluation

1(a) 1 °C 1 1(b) M1: diagram of labelled polystyrene cup in a beaker AND containing labelled aqueous copper(II) sulfate 2 M2: diagram of free-standing labelled thermometer with bulb clearly within the solution 1(c) M1: plots after 4 mins and curved line of best fit back from 10 mins to 5 min 2 M1: extrapolation to 4 mins and correct subtraction to determine ΔT 1(d) M1: energy released = –25.(0) × 4.18 × ΔT in 1(c) = (–2560.5) J 2 M2: enthalpy change of reaction = (M1 / 1000) / 1.25 × 10–2 = –205 (kJ mol–1) 1(e)(i) no change / effect 1 AND zinc is (already) in excess 1(e)(ii) (heat loss) increases 1 AND increased energy output / temperature rise OR more exothermic change occurs 1(e)(iii) no change / effect 1 AND twice the energy output nullified / cancelled out by twice the volume of water to be heated Question Answer Marks

2(a) M1: (250 cm3) volumetric flask 4 M2: dissolve the solid / acid salt (1.89 g) (in the beaker) (using distilled) water M3: transfer / add to a (250 cm3 volumetric) flask AND rinse (with distilled water) M4: top up to mark (with distilled water) 2(b)(i) to ensure that (exactly) 25.0 cm3 of solution has been delivered into the flask 1 2(b)(ii) measuring cylinder 1 2(b)(iii) difficult to see the 0.00 cm3 line 1 2(b)(iv) (two) titres / readings within 0.1(0) (cm3) of each other 1 © UCLES 2021 Page 5 of 6 2(b)(v) colourless to pale purple 1 2(b)(vi) M1: mol MnO –(aq) = 0.0200 × 24.40 / 1000 = 4.88 × 10–4 (mol) 3 4 M2: mol of C O 2–(aq) (in 25.0 cm3) = M1 × 5 / 2 = 1.22 × 10–3 (mol) 2 4 M3: mol of C O 2–(aq) (in solution A) = M2 × 250 / 25 = 1.22 × 10–2 (mol) 2 4 2(c)(i) (aqueous) sodium hydroxide 1 2(c)(ii) M1: mol H+(aq) in 250 cm3 = 6.10 × 10–2 / 4 = 1.525 × 10–2 (mol) 3 M2: ratio C O 2–(aq) : H+(aq) 2 4 (1.22 × 10–2 / 1.22 × 10–2) : 1.525 × 10–2 / 1.22 × 10–2 = 1 : 1.25 and b = 1.25 M3: 2 – 1.25 a = 0.75 2(c)(iii) M1: M of hydrated K H C O •dH O = 1.89 / 1.22 × 10–2 = 154.9 2 r 0.75 1.25 2 4 2 OR M of anhydrous K H C O = [(0.75 × 39.1) + (1.25 × 1.0) + (2 × 12.0) + (4 × 16.0)] = 118.575 r 0.75 1.25 2 4 M2: mass of water = hydrated mass – anhydrous mass = 154.9 – 118.575 = 36.325 AND 36.325 / 18 = 2 2(d) M1: initial readings 2 mass of (empty) crucible / g mass of crucible + crystals before heating / g mass of crucible + crystals after heating / g M2: second reading of mass of crucible + crystals after re-heating © UCLES 2021 Page 6 of 6

1(a)(i) the metal oxide 1 1(a)(ii) count bubbles in a set time 1 OR measure volume (of oxygen) in a certain time OR measure time to produce a certain volume 1(b) Any two from: 2 the volume of the hydrogen peroxide / solution the concentration of the hydrogen peroxide temperature particle size 1(c) correctly drawn diagram showing: 3 M1: contents of flask M2: sealed apparatus M3: collection of the gas in a measuring cylinder (graduations assumed) (via a delivery tube into water) / gas syringe 1(d)(i) volume of gas / oxygen AND time 1 1(d)(ii) plot a (volume / time) graph AND measure gradient / produce a tangent at t = 0 or at the start 1 1(e) repeat (the experiments / trials) (until consistent results) 1 © UCLES 2021 Page 5 of 9 1(f) measuring the decrease / change in (total) mass of the solution / mixture / reaction vessel (and contents) (and time) 1 OR measuring the mass / weight of the mixture/reaction vessel (and contents) AND time 1(g) M1: (filter/remove) dry the residue/metal oxide 2 M2: weigh the residue / metal oxide to see if the mass is unchanged OR M1: re-use with new hydrogen peroxide / do the same reaction again with the same catalyst M2: and check if the gas volumes identical / rate of reaction the same 1(h) to allow the oxygen / gas (that is formed) to be released / escape / diffuse out 1 Question Answer Marks

2(a)(i) M KMnO = 158.0 1 r 4 500 × 0.02 / 1000 = 0.01 0.01 × 158.0 = 1.58 g 2(a)(ii) (2 × 0.005 / 1.58) × 100 = 0.63% 1 2(a)(iii) rinse the solid off the weighing boat into the beaker 1 OR weighing the mass directly into the beaker OR (re)-weigh the weighing boat after transferring the KMnO into the beaker 4 2(a)(iv) Any two from: 2 stir / agitate / mix (to ensure that the solid has dissolved) rinse the beaker and transfer the washings shaking / inverting / homogenising of volumetric solution © UCLES 2021 Page 6 of 9 2(b)(i) rinse / run through / wash the burette with some of the KMnO solution 1 4 OR run some of the KMnO solution from the burette to fill to the tip 4 2(b)(ii) add the KMnO dropwise (near the end point) 1 4 2(c)(i) the Fe2+(aq) / Fe3+(aq) mixture measured using a measuring cylinder 1 AND leads to increased likelihood of non-concordant titres 2(c)(ii) (measure the volume) using a (volumetric / 25 cm3) pipette 1 © UCLES 2021 Page 7 of 9 2(d)(i) Set A 2 rough titration 1 titration 2 titration 3 final volume / cm3 18.40 17.25 34.55 18.00 initial volume / cm3 0.65 0.15 17.25 0.95 titre / cm3 17.75 17.10 17.30 17.05 mean titre = 17.1 (cm3) Set B rough titration 1 titration 2 final volume / cm3 45.05 43.60 43.70 initial volume / cm3 0.20 0.15 0.10 titre / cm3 44.85 43.45 43.60 mean titre = 43.5 (cm3) M1: correct titres (to 2 decimal places) M2: correct means 2(d)(ii) M1: 2 n MnO – (aq) = 43.5 × 0.02 / 1000 = 8.70 × 10–4 4 n Fe2+ (aq) = 8.70 × 10–4 × 5 = 4.35 × 10–3 M2: 100 mass of Fe 2+ (aq) = 4.35 × 10–3 × 55.8 × = 0.971 g 25 © UCLES 2021 Page 8 of 9 2(d)(iii) n MnO - (aq) = 17.1 × 0.02 / 1000 = 3.42 × 10–4 1 4 n Fe2+ (aq) = 3.42 × 10–4 × 5 = 1.71 × 10–3 250 mass of Fe 2+ (aq) = 1.71 × 10–3 × 55.8 × = 0.954 g 25 2(d)(iv) 250 250 1 % Fe3+ = ((2(d)(ii) × ) – 2(d)(iii))/(2(d)(ii) × )) × 100% 100 100 OR (2(d)(ii) × 2.5 – 2(d)(iii)) / (2(d)(ii) × 2.5) × 100% 2(d)(v) reduce / use (in step 6) more than 100 cm3 of solution (Fe2+ and Fe3+) 1 © UCLES 2021 Page 9 of 9

1(a) negative 1 AND bond formation is happening (between MgSO and H O) 4 2 1(b)(i) 8.05(°C) 1 1(b)(ii) to allow the temperature of the water to equilibrate with room temperature 1 1(b)(iii) M1: (measure) 50 cm3 (distilled) water and transfer into a polystyrene / polyfoam / plastic cup 4 M2: measure the temperature of the water at (30 second) intervals (until constant / before adding MgSO ) 4 M3: MgSO added at 180 s / 3 minutes 4 M4: stir and measure the temperature of the water at (30 second) intervals (until at least 8 mins have elapsed since time 0) 1(c)(i) 0.025 × 7 × 18 = 3.15 1 AND 50.00 – 3.15 = 46.85 (cm3) 1(c)(ii) M1: burette 2 M2: (apparatus) measures to 0.05 (cm3) 1(d) use a larger number of moles (of hydrated magnesium sulfate/solid) 1 OR use a smaller volume of distilled water © UCLES 2021 Page 5 of 9 1(e)(i) M1: 2 ΔH = –2125 / 1000 × 0.025 = –85.0 exp1 and ΔH = 477.5 / 1000 × 0.025 = 19.1 exp2 M2: ΔH = ΔH – ΔH exp1 exp2 –85.0 – (+)19.1 = –104.1 kJ mol–1 1(e)(ii) less exothermic 1 AND fewer moles reacted Question Answer Marks

2(a) butanoic acid is flammable 1 2(b)(i) 250.(0) cm3 1 2(b)(ii) M1: dissolve the solid / sodium butanoate (55.0 g) (in the beaker) (using a small volume of) (distilled) water M2: transfer / add to a (250 cm3 volumetric) flask AND rinse (with distilled water) M3: top the 250 cm3 volumetric flask up to mark (with distilled water) © UCLES 2021 Page 6 of 9 2(b)(iii) 2 moles of volume of moles of volume of volume of acid acid base base water 0.050 25.0 0.005 2.5 22.5 0.050 25.0 0.008 4.0 21.0 0.050 25.0 0.010 5.0 20.0 0.050 25.0 0.025 12.5 12.5 0.030 15.0 0.050 25.0 10.0 0.010 5.0 0.050 25.0 20.0 0.006 3.0 0.050 25.0 22.0 0.004 2.0 0.050 25.0 23.0 M1: column 4 M2: column 5 © UCLES 2021 Page 7 of 9 2(c)(i) 1 ratio of –log [acid] moles of acid moles of base pH [acid] / [base] [base] 0.050 0.005 10.00 –1.00 3.82 0.050 0.008 6.25 –0.80 4.01 0.050 0.010 5.00 –0.70 4.12 0.050 0.025 2.00 –0.30 4.70 0.030 0.050 0.60 (+)0.22 5.04 0.010 0.050 0.20 (+)0.70 5.52 0.006 0.050 0.12 (+)0.92 5.74 0.004 0.050 0.08 (+)1.10 5.91 2(c)(ii) M1: 8 points plotted correctly 2 M2: straight line of best fit drawn which must extend to cover all data points © UCLES 2021 Page 8 of 9 2(c)(iii) M1: Plot at –0.3, 4.70 2 M2: (actual) moles of acid (in the buffer) is lower (than recorded in the table) OR (actual) moles of base (in the buffer) is higher (than recorded in the table) OR concentration of acid (in buffer) lower (than they think for this reading) OR concentration of base (in buffer) higher (than they think for this reading) OR volume of acid used (to make the buffer) is lower (than recorded in table / 25 cm3) OR volume of base used (to make the buffer) is higher (than recorded in table / 12.5 cm3) 2(c)(iv) pK = 4.82 1 a 2(c)(v) M1: K = 1.51 × 10–5 (must be 3 SF) 2 a M2: mol dm–3 2(d) endothermic 1 AND K increases (with increasing temperature) a © UCLES 2021 Page 9 of 9

1(a)(i) the metal oxide 1 1(a)(ii) count bubbles in a set time 1 OR measure volume (of oxygen) in a certain time OR measure time to produce a certain volume 1(b) Any two from: 2 the volume of the hydrogen peroxide / solution the concentration of the hydrogen peroxide temperature particle size 1(c) correctly drawn diagram showing: 3 M1: contents of flask M2: sealed apparatus M3: collection of the gas in a measuring cylinder (graduations assumed) (via a delivery tube into water) / gas syringe 1(d)(i) volume of gas / oxygen AND time 1 1(d)(ii) plot a (volume / time) graph AND measure gradient / produce a tangent at t = 0 or at the start 1 1(e) repeat (the experiments / trials) (until consistent results) 1 © UCLES 2021 Page 5 of 9 1(f) measuring the decrease / change in (total) mass of the solution / mixture / reaction vessel (and contents) (and time) 1 OR measuring the mass / weight of the mixture/reaction vessel (and contents) AND time 1(g) M1: (filter/remove) dry the residue/metal oxide 2 M2: weigh the residue / metal oxide to see if the mass is unchanged OR M1: re-use with new hydrogen peroxide / do the same reaction again with the same catalyst M2: and check if the gas volumes identical / rate of reaction the same 1(h) to allow the oxygen / gas (that is formed) to be released / escape / diffuse out 1 Question Answer Marks

2(a)(i) M KMnO = 158.0 1 r 4 500 × 0.02 / 1000 = 0.01 0.01 × 158.0 = 1.58 g 2(a)(ii) (2 × 0.005 / 1.58) × 100 = 0.63% 1 2(a)(iii) rinse the solid off the weighing boat into the beaker 1 OR weighing the mass directly into the beaker OR (re)-weigh the weighing boat after transferring the KMnO into the beaker 4 2(a)(iv) Any two from: 2 stir / agitate / mix (to ensure that the solid has dissolved) rinse the beaker and transfer the washings shaking / inverting / homogenising of volumetric solution © UCLES 2021 Page 6 of 9 2(b)(i) rinse / run through / wash the burette with some of the KMnO solution 1 4 OR run some of the KMnO solution from the burette to fill to the tip 4 2(b)(ii) add the KMnO dropwise (near the end point) 1 4 2(c)(i) the Fe2+(aq) / Fe3+(aq) mixture measured using a measuring cylinder 1 AND leads to increased likelihood of non-concordant titres 2(c)(ii) (measure the volume) using a (volumetric / 25 cm3) pipette 1 © UCLES 2021 Page 7 of 9 2(d)(i) Set A 2 rough titration 1 titration 2 titration 3 final volume / cm3 18.40 17.25 34.55 18.00 initial volume / cm3 0.65 0.15 17.25 0.95 titre / cm3 17.75 17.10 17.30 17.05 mean titre = 17.1 (cm3) Set B rough titration 1 titration 2 final volume / cm3 45.05 43.60 43.70 initial volume / cm3 0.20 0.15 0.10 titre / cm3 44.85 43.45 43.60 mean titre = 43.5 (cm3) M1: correct titres (to 2 decimal places) M2: correct means 2(d)(ii) M1: 2 n MnO – (aq) = 43.5 × 0.02 / 1000 = 8.70 × 10–4 4 n Fe2+ (aq) = 8.70 × 10–4 × 5 = 4.35 × 10–3 M2: 100 mass of Fe 2+ (aq) = 4.35 × 10–3 × 55.8 × = 0.971 g 25 © UCLES 2021 Page 8 of 9 2(d)(iii) n MnO - (aq) = 17.1 × 0.02 / 1000 = 3.42 × 10–4 1 4 n Fe2+ (aq) = 3.42 × 10–4 × 5 = 1.71 × 10–3 250 mass of Fe 2+ (aq) = 1.71 × 10–3 × 55.8 × = 0.954 g 25 2(d)(iv) 250 250 1 % Fe3+ = ((2(d)(ii) × ) – 2(d)(iii))/(2(d)(ii) × )) × 100% 100 100 OR (2(d)(ii) × 2.5 – 2(d)(iii)) / (2(d)(ii) × 2.5) × 100% 2(d)(v) reduce / use (in step 6) more than 100 cm3 of solution (Fe2+ and Fe3+) 1 © UCLES 2021 Page 9 of 9

1(a) It is not possible to measure a temperature when heating. 1 1(b)(i) Mass of KHCO = 2.503 g 1 3 AND Mass of K CO = 3.455 g 2 3 1(b)(ii) 2 ×0.0005 ×100 1 = = 0.04(00)% 2.503 Correct working must be shown 1(c)(i) M1 3.5 °C for KHCO and1.5 °C for K CO in results table 2 3 2 3 AND q = 50 × 4.18 × 3.5 = 731.5 (J) M2 ΔH = M1 / (0.0250 × 1000) = + 29.26 kJ mol–1 1 1(c)(ii) M1 q = K CO = 50 × 4.18 × 1.5 = 313.5 (J) 2 2 3 M1 M2 ΔH = − = –12.54 kJ mol–1 2 0.025 ×1000 1(d) M1 2 × 1(c)(i) = 2 × 29.26 = 58.52 kJ mol–1 2 M2 M1 – 1(c)(ii) = +58.52 – (–12.54) = +71.06 kJ mol–1 1(e) Any two from: 2 • Heat loss OR heat gain (to / from surroundings) • Amount of solid not exactly 0.0250 moles • Experiment not carried out under standard conditions. © UCLES 2021 Page 5 of 8 1(f) Add a lid to the polystyrene cup. 1 1(g) Burette. 1 1(h) Wear chemically resistant gloves 1 AND Reagent(s) are irritant(s). © UCLES 2021 Page 6 of 8

2(a) M1 Addition of solid and acid must not lead to initial escape of gas from sealed system or produce excess volume 3 measurement leading to a false volume reading e.g. Adding acid to solid already in the flask or vice versa. M2 Allow any leakproof apparatus capable of delivering a sample of gas into one collection vessel over water. M3 A vertical inverted measuring cylinder or burette filled with water positioned to collect the gas (via delivery tube). 2(b)(i) 1 V – V / cm3 final t 93 71 56 43 32 25 18 15 14 6 3 0 93, 71, 56, 43, 32, 25, 18, 15, 14, 6, 3, 0 © UCLES 2021 Page 7 of 8 2(b)(ii) M1 Selects and labels appropriate linear scales for axes AND All points plotted correctly AND covering at least half of the 2 grid for each axis. M2 Smooth curve of best fit line drawn going through most points. 2(b)(iii) The point at 240 s. 1 2(b)(iv) The volume of gas may have been read before 240 . 1 2(b)(v) M1 Suitable construction lines shown on the graph. 2 M2: Two half-lives read correctly from graph AND mean half-life calculated using values read correctly from graph. (Likely to be approx. 78 s) 2(b)(vi) 0.693 1 = average 𝑡 calculated in 2(b)(v) (cid:2869)/(cid:2870) 2(c) The value of k would increase 1 AND as t would decrease. ½ 2(d)(i) M1 Table complete with four different sets of values that would produce different concentrations, total volume = 50 cm3 2 AND All volumes of 2.0 mol dm–3 acid must be 10 cm3 or greater (to ensure an excess). M2 All concentrations correctly calculated. 2(d)(ii) time (taken for fizzing to stop) 1 2(d)(iii) The experiment should be repeated to identify / eliminate anomalies. 1 © UCLES 2021 Page 8 of 8

1(a) 20.1 °C AND 0.53 g 1 1(b) 0.53 / 46 = 0.0115 (mol) 1 1(c) M1 q = 100 × 4.18 × 20.1 = 8401.8 J 2 M2 ΔH = 8401.8 / 0.0115 × 1000 = –731 (kJ mol–1) c 1(d) (2 × 0.05) / 20.1 × 100 = 0.498% 1 Working must be shown 1(e) (accuracy would) increase 1 and the percentage error (for temperature / calculated mass of ethanol) is reduced (accuracy would) decrease and More heat loss (due to high temperature rise) 1(f) M1 (ΔH ) would be less exothermic / less negative 2 c M2 moles (of ethanol) ‘combusted’ / ‘used’ (will appear to) increase (due to evaporation) 1(g)(i) M1 heat loss (to the surroundings) 2 M2 incomplete combustion 1(g)(ii) bond enthalpies vary according to compound / molecule (the bond is situated in) 1 OR average bond enthalpies assume ethanol / water / substances are gaseous © UCLES 2021 Page 5 of 7

2(a) M1 (substances) are flammable 2 M2 to control the temperature (of the reaction) 2(b) Wear chemically resistant gloves 1 2(c) To allow the halogenoalkane and sodium hydroxide to mix / react 1 2(d) To indicate (the time) when the sodium hydroxide has been used up. 1 2(e)(i) 2.40 × 10–3 1 4.20 × 10–3 7.41 × 10–3 2(e)(ii) (1/t / rate of reaction increases from chlorobutane to iodobutane) bond enthalpy of carbon halogen bond decreases from 1 C–Cl to C–I 2(f) The concentration of sodium hydroxide. 1 2(g)(i) M1 12 points plotted correctly 2 M2 Curved line of best fit to cover data points 2(g)(ii) point at t = 480 s 1 2(g)(iii) Step 4 was omitted 1 2(g)(iv) M1 Suitable construction lines shown on the graph. 2 M2 Two half-lives correctly determined. 2(g)(v) Yes 1 AND half-life is constant © UCLES 2021 Page 6 of 7 2(h)(i) (10 cm3) Pipette 1 2(h)(ii) Insufficient (volume of) reaction mixture 1 2(h)(iii) To quench the reaction 1 2(i) The electrical conductivity of the mixture would not change enough to be measured (in a chemistry laboratory) 1 © UCLES 2021 Page 7 of 7

1(a) It is not possible to measure a temperature when heating. 1 1(b)(i) Mass of KHCO = 2.503 g 1 3 AND Mass of K CO = 3.455 g 2 3 1(b)(ii) 2 ×0.0005 ×100 1 = = 0.04(00)% 2.503 Correct working must be shown 1(c)(i) M1 3.5 °C for KHCO and1.5 °C for K CO in results table 2 3 2 3 AND q = 50 × 4.18 × 3.5 = 731.5 (J) M2 ΔH = M1 / (0.0250 × 1000) = + 29.26 kJ mol–1 1 1(c)(ii) M1 q = K CO = 50 × 4.18 × 1.5 = 313.5 (J) 2 2 3 M1 M2 ΔH = − = –12.54 kJ mol–1 2 0.025 ×1000 1(d) M1 2 × 1(c)(i) = 2 × 29.26 = 58.52 kJ mol–1 2 M2 M1 – 1(c)(ii) = +58.52 – (–12.54) = +71.06 kJ mol–1 1(e) Any two from: 2 • Heat loss OR heat gain (to / from surroundings) • Amount of solid not exactly 0.0250 moles • Experiment not carried out under standard conditions. © UCLES 2021 Page 5 of 8 1(f) Add a lid to the polystyrene cup. 1 1(g) Burette. 1 1(h) Wear chemically resistant gloves 1 AND Reagent(s) are irritant(s). © UCLES 2021 Page 6 of 8

2(a) M1 Addition of solid and acid must not lead to initial escape of gas from sealed system or produce excess volume 3 measurement leading to a false volume reading e.g. Adding acid to solid already in the flask or vice versa. M2 Allow any leakproof apparatus capable of delivering a sample of gas into one collection vessel over water. M3 A vertical inverted measuring cylinder or burette filled with water positioned to collect the gas (via delivery tube). 2(b)(i) 1 V – V / cm3 final t 93 71 56 43 32 25 18 15 14 6 3 0 93, 71, 56, 43, 32, 25, 18, 15, 14, 6, 3, 0 © UCLES 2021 Page 7 of 8 2(b)(ii) M1 Selects and labels appropriate linear scales for axes AND All points plotted correctly AND covering at least half of the 2 grid for each axis. M2 Smooth curve of best fit line drawn going through most points. 2(b)(iii) The point at 240 s. 1 2(b)(iv) The volume of gas may have been read before 240 . 1 2(b)(v) M1 Suitable construction lines shown on the graph. 2 M2: Two half-lives read correctly from graph AND mean half-life calculated using values read correctly from graph. (Likely to be approx. 78 s) 2(b)(vi) 0.693 1 = average 𝑡 calculated in 2(b)(v) (cid:2869)/(cid:2870) 2(c) The value of k would increase 1 AND as t would decrease. ½ 2(d)(i) M1 Table complete with four different sets of values that would produce different concentrations, total volume = 50 cm3 2 AND All volumes of 2.0 mol dm–3 acid must be 10 cm3 or greater (to ensure an excess). M2 All concentrations correctly calculated. 2(d)(ii) time (taken for fizzing to stop) 1 2(d)(iii) The experiment should be repeated to identify / eliminate anomalies. 1 © UCLES 2021 Page 8 of 8

1(a) allow (crucible / contents) to cool 1 1(b) to prevent spitting of crystals 1 1(c) pipe-clay triangle 1 1(d) heat to constant mass 1 1(e)(i) M1: (mass H O) = 3.15 (g) AND (mass CuSO ) = 4.34 (g) 3 2 4 M2: n(H O) = 3.15 / 18 = 0.175 2 AND n(CuSO ) = 4.34 / 159.6 = 0.02719… 4 M3: 0.02719… / 0.02719… AND 0.175 / 0.02719… = 6.44 1(e)(ii) If value of x in 1(e)(i) is above 5: 1 CuSO must have decomposed / crystals were wet before heating / some crystals were lost when heated (e.g. during 4 spitting) / impurity that decomposes or evaporates If value of x in 1(e)(i) is below 5: did not heat it enough / not all water driven off / unreactive impurity 1(f) [(2 × 0.005) / 13.60] × 100 = 0.0735 (%) 1 © UCLES 2022 Page 5 of 7

2(a)(i) solution of known concentration 1 2(a)(ii) M1: measure 28.55 cm3 of CH COOH 4 3 M2: using burette / graduated pipette M3: (transfer/add CH COOH to) a 250 cm3 volumetric flask 3 M4: top the (volumetric) flask up to (250 cm3) mark with distilled water 2(b) (pure) CH COOH is corrosive 1 3 2(c)(i) 2 3 4 4.47 0.0752 6.32 0.110 8.94 0.154 12.6 0.213 17.9 0.368 25.3 0.428 M1: column 3 all values to 3 SF M2: column 4 all values to 3 SF 2(c)(ii) conductivity 1 2(c)(iii) to calibrate the conductivity meter 1 2(c)(iv) temperature 1 2(d) M1: 6 points plotted correctly 2 M2: line of best fit drawn © UCLES 2022 Page 6 of 7 2(e) M1: 5th point circled at 17.9, 0.368 2 M2: ethanoic acid was diluted incorrectly 2(f)(i) M1: co-ordinates read and recorded correctly 2 M2: gradient calculated to 3 SF 2(f)(ii) M1: (gradient calculated in (f)(i) / 3.91)2 2 (0.0169 / 3.91)2 = 1.87 × 10–5 M2: mol dm–3 2(g) M1: percentage error of experimental value = [(1.34 – 1.28) / 1.34] × 100 = 4.5% 2 M2: valid and the calculated actual percentage error is less than the maximum percentage error © UCLES 2022 Page 7 of 7

1(a) 250.0 1 number of moles NaCl =  0.200 = 0.05(00) 1000 mass of sodium chloride = 0.05(00)  (23.0 + 35.5) = 2.925 g 1(b) (measure mass of weighing boat containing sodium chloride before transfer, then) 1 measure the mass of weighing boat (and residue) (after transfer). 1(c) M1 2 add a (small) volume of distilled water (to the small beaker) AND dissolve the sodium chloride M2 transfer the solution and washings into a 250 cm3 volumetric flask AND make up to the mark with distilled water © UCLES 2022 Page 5 of 10 1(d)(i) M1 Extra step 2 wash the precipitate / residue (with cold distilled water) a OR reheat (and reweigh) until mass is constant b OR rinse the beaker into filter (washings) c OR filter solution again d M2 Explanation to remove (unreacted) sodium chloride and/or lead compound a OR to ensure all water has been removed from the solid b OR to ensure all solid/ppt has been transferred into the filter c OR to collect any precipitate that passed through the filter paper first time d 1(d)(ii) 20.05 1 100 = 1(.0%) 10 correct working must be shown 1(d)(iii) repeat the experiment and/or compare with results from other students 1 AND consistent results are obtained © UCLES 2022 Page 6 of 10 1(e)(i) Two appropriate straight lines of best fit drawn that intersect. 1 1(e)(ii) M1 volume of intersection correctly read from graph plotted in (e)(i). 2 (expected volumes: NaCl(aq) ≈ 33.25 cm3, lead compound(aq) ≈ 16.75 cm3) M2 molar ratio consistent with volumes given for M1. (expected ratio = 2 : 1) 1(f) empirical formula consistent with molar ratio given in (e)(ii). 1 (expected answer: PbCl ) 2 © UCLES 2022 Page 7 of 10 1(g) investigation 1 2 repeat measurement (of height of precipitate) until it is constant OR leave (for a longer time) until height of precipitate is constant (before measuring) investigation 2 use a smaller volume of lead compound (in each case) OR add larger volumes of sodium chloride (until it is in excess) Question Answer Marks

2(a)(i) thermostatically controlled water bath 1 2(a)(ii) flammable substance(s) are used (in the experiment) 1 2(b)(i) (50 cm3) burette 1 2(b)(ii) 10(.00) cm3 (volumetric) pipette 1 2(c) reduces the reaction rate (of hydrolysis reaction) 1 OR quenches the reaction 2(d) volume of sodium hydroxide (solution used in titration) 1 © UCLES 2022 Page 8 of 10 2(e)(i) 1 time / s titre, V / cm3 V – V / cm3 t final t 60 1.25 46.00 300 7.75 39.50 600 17.75 29.50 900 20.00 27.25 1200 24.25 23.00 1500 28.40 18.85 1800 31.15 16.10 2700 38.00 9.25 Final 47.25 (0.00) 2(e)(ii) concentration of the 2-bromo-2-methylpropane 1 2(e)(iii) M1 all points plotted correctly 2 M2 smooth curve of best fit line drawn passing close to all points except anomaly 2(e)(iv) M1 selects the point most anomalous to the plotted line of best fit 2 (point at 600, 29.5 expected) M2 reaction was not effectively quenched © UCLES 2022 Page 9 of 10 2(e)(v) M1 3 correctly placed construction lines shown on the graph to determine at least one half-life correctly OR both co-ordinates from line of best fit correctly recorded in the form (x,y) for either first t OR second t ½ ½ M2 two sets of co-ordinates from line of best fit correctly recorded for first t AND second t in the form (x,y) ½ ½ M3 two half-lives correctly calculated from listed co-ordinates (expected value: 1159 s) 2(e)(vi) first order 1 AND half-lives are constant (within experimental error) © UCLES 2022 Page 10 of 10

1(a) M1 sealed apparatus 2 M2 collection of the gas in a labelled inverted (250 cm3) measuring cylinder (via a delivery tube into water) 1(b)(i) remove oxide layer by using sandpaper 1 1(b)(ii) mass (of Mg) 1 1(c)(i) Method 1 2 M1 mol HCl used = 0.50  30 / 1000 OR 0.015 mol M2 mass Mg needed = 0.015 / 2  24.3 = 0.18(225) g Method 2 M1 mol of Mg used = 0.16 / 24.3 OR 0.00658(436) M2 vol of HCl needed = 0.00658 …  2  1000 / .50 = 26.3 cm3 1(c)(ii) acid is in excess 1 1(d) to make sure the gas is at room temperature 1 1(e)(i) 1  100 / 146 = 0.68(49..%) 1 1(e)(ii) 146 / (0.16 / 24.3) = 22 174 cm3 1 1(f) M1 weakness 2 loss of hydrogen/gas before the flask is stoppered OR between steps 4 and 5 M2 improvement ensure reagents are separate within sealed flask before mixing © UCLES 2022 Page 5 of 7

2(a) temperature 1 2(b) Any two from: 2 volume of H O (aq) 2 2 concentration of H O (aq) 2 2 volume of KI(aq) / catalyst concentration of KI(aq) / catalyst 2(c)(i) M1 50(.0) cm3 of H O 3 2 2 M2 using burette transfer / add to a (250 cm3) volumetric flask M3 top the (volumetric) flask up to (250 cm3) mark with distilled water 2(c)(ii) use chemically resistant gloves 1 2(d)(i) 2 temp 1 / T / K–1 initial rate / mol s–1 log initial rate 293 0.00341 5.75  10–6 –5.24 298 0.00336 7.94  10–6 –5.10 303 0.00330 1.17  10-5 –4.93 308 0.00325 1.45  10–5 –4.84 312 0.00321 2.19  10–5 –4.66 319 0.00313 3.72  10–5 –4.43 325 0.00308 5.25  10–5 –4.28 328 0.00305 6.31  10–5 –4.20 M1 1/T column correct to three significant figures M2 log initial rate column correct to three significant figures © UCLES 2022 Page 6 of 7 2(d)(ii) M1 8 points plotted correctly 2 M2 line of best fit drawn 2(d)(iii) M1 most anomalous point circled 2 M2 the recorded temperature (reading) is higher than the actual temperature for that set of readings 2(d)(iv) M1 co-ordinates read and recorded correctly 2 M2 gradient calculated to three significant figures 2(d)(v) M1 gradient = – E / 2.303R OR any correct rearrangement of this 2 a M2 Correct calculation of E a 2(e) no AND there is an anomalous point on the graph 1 © UCLES 2022 Page 7 of 7

1(a) 250.0 1 number of moles NaCl =  0.200 = 0.05(00) 1000 mass of sodium chloride = 0.05(00)  (23.0 + 35.5) = 2.925 g 1(b) (measure mass of weighing boat containing sodium chloride before transfer, then) 1 measure the mass of weighing boat (and residue) (after transfer). 1(c) M1 2 add a (small) volume of distilled water (to the small beaker) AND dissolve the sodium chloride M2 transfer the solution and washings into a 250 cm3 volumetric flask AND make up to the mark with distilled water © UCLES 2022 Page 5 of 10 1(d)(i) M1 Extra step 2 wash the precipitate / residue (with cold distilled water) a OR reheat (and reweigh) until mass is constant b OR rinse the beaker into filter (washings) c OR filter solution again d M2 Explanation to remove (unreacted) sodium chloride and/or lead compound a OR to ensure all water has been removed from the solid b OR to ensure all solid/ppt has been transferred into the filter c OR to collect any precipitate that passed through the filter paper first time d 1(d)(ii) 20.05 1 100 = 1(.0%) 10 correct working must be shown 1(d)(iii) repeat the experiment and/or compare with results from other students 1 AND consistent results are obtained © UCLES 2022 Page 6 of 10 1(e)(i) Two appropriate straight lines of best fit drawn that intersect. 1 1(e)(ii) M1 volume of intersection correctly read from graph plotted in (e)(i). 2 (expected volumes: NaCl(aq) ≈ 33.25 cm3, lead compound(aq) ≈ 16.75 cm3) M2 molar ratio consistent with volumes given for M1. (expected ratio = 2 : 1) 1(f) empirical formula consistent with molar ratio given in (e)(ii). 1 (expected answer: PbCl ) 2 © UCLES 2022 Page 7 of 10 1(g) investigation 1 2 repeat measurement (of height of precipitate) until it is constant OR leave (for a longer time) until height of precipitate is constant (before measuring) investigation 2 use a smaller volume of lead compound (in each case) OR add larger volumes of sodium chloride (until it is in excess) Question Answer Marks

2(a)(i) thermostatically controlled water bath 1 2(a)(ii) flammable substance(s) are used (in the experiment) 1 2(b)(i) (50 cm3) burette 1 2(b)(ii) 10(.00) cm3 (volumetric) pipette 1 2(c) reduces the reaction rate (of hydrolysis reaction) 1 OR quenches the reaction 2(d) volume of sodium hydroxide (solution used in titration) 1 © UCLES 2022 Page 8 of 10 2(e)(i) 1 time / s titre, V / cm3 V – V / cm3 t final t 60 1.25 46.00 300 7.75 39.50 600 17.75 29.50 900 20.00 27.25 1200 24.25 23.00 1500 28.40 18.85 1800 31.15 16.10 2700 38.00 9.25 Final 47.25 (0.00) 2(e)(ii) concentration of the 2-bromo-2-methylpropane 1 2(e)(iii) M1 all points plotted correctly 2 M2 smooth curve of best fit line drawn passing close to all points except anomaly 2(e)(iv) M1 selects the point most anomalous to the plotted line of best fit 2 (point at 600, 29.5 expected) M2 reaction was not effectively quenched © UCLES 2022 Page 9 of 10 2(e)(v) M1 3 correctly placed construction lines shown on the graph to determine at least one half-life correctly OR both co-ordinates from line of best fit correctly recorded in the form (x,y) for either first t OR second t ½ ½ M2 two sets of co-ordinates from line of best fit correctly recorded for first t AND second t in the form (x,y) ½ ½ M3 two half-lives correctly calculated from listed co-ordinates (expected value: 1159 s) 2(e)(vi) first order 1 AND half-lives are constant (within experimental error) © UCLES 2022 Page 10 of 10

1(a)(i) (no. moles of AgCl formed = 3.63 / 143.4 1 = 0.02531381) no. moles MgCl in the sample = 0.02531381 / 2 2 = 0.0126569 answer to at least 2SF 1(a)(ii) M1: mass of MgCl = answer to (a)(i)  95.3 1 2 (= 1.2062 g) M2: % by mass = (M1 /1.52)  100 = (79.355%) 1 answer to at least 2SF 1(b)(i) stir (when solid is mixed with water) 1 OR increase temperature (of water) OR increase state of division of the (solid) mixture 1(b)(ii) to remove magnesium nitrate / (excess) silver nitrate (from the precipitate before drying) 1 1(b)(iii) (It is dried in an oven) to avoid (thermal) decomposition (of silver chloride / precipitate / solid) 1 1(c)(i) ((2  0.005) / 1.52)  100 (= 0.66%) (0.6578947) 1 correct working must be shown along with correct answer. answer to at least 1SF 1(c)(ii) use a larger mass of solid (mixture). 1 1(c)(iii) (continue drying and) reweigh until mass remains constant 1 © UCLES 2022 Page 5 of 8 1(d) the (measured) mass / amount (of ‘AgCl ’ / solid / precipitate) would be greater (than the true value) 1 AND the % by mass (of MgCl in the sample) would be greater (than the true value) 2 Question Answer Marks

2(a) (wear) chemically resistant gloves. 1 2(b)(i) M1 leakproof apparatus capable of delivering a sample of gas (for collection over water) 1 M2: a suitable collection vessel filled with water correctly positioned in a water containing trough to collect the gas (via 1 delivery tube) 2(b)(ii) do not collect the first gas to be delivered 1 © UCLES 2022 Page 6 of 8 2(c)(i) M1: all points plotted correctly 1 M2: line of best fit drawn 1 2(c)(ii) M1: two acceptable coordinates from LOBF expressed in the form (x,y) 1 M2: gradient correctly calculated from points listed for M1 1 (≈ 0.357 cm3 K–1) answer correctly rounded to 3SF 2(d)(i) ring drawn around point at 308 K and 88 cm3 1 2(d)(ii) the (actual) temperature was higher than the recorded / measured temperature / 308K / 35 °C 1 2(e)(i) (absolute) temperature (of the gas) 1 2(e)(ii) more (repeated) measurements should be taken 1 AND anomalies identified / eliminated 2(f) gradient is smaller / line is less steep (for smaller volume of oxygen at start of experiment) 1 AND gradient = nR/P © UCLES 2022 Page 7 of 8

3(a)(i) description of a (clock) method to measure the time taken for a particular amount of product (Br ) to be produced 1 2 3(a)(ii) X = 1, Y = 1 and Z = 2 2 all 3 correct = ✓✓ 2 correct = ✓ 1 or 0 correct = × 3(b) burette 1 3(c) (changing) the temperature (of the reagents) will affect the rate of reaction (so it must be kept constant) 1 3(d) M1: measure (a volume of) 1 moldm-3 sulfuric acid using a burette into a volumetric flask 1 AND make up to the (calibration) mark with distilled water M2: (0.15  a) cm3 of 1 mol dm-3 sulfuric acid is measured to make up a cm3 (of the diluted solution) 1 © UCLES 2022 Page 8 of 8

1(a)(i) (reheat and) reweigh until mass remains constant 1 1(a)(ii) increases the rate of reaction 1 And due to increase the surface area 1(a)(iii) to ensure the reaction is complete 1 1(b)(i) M1: 16.55 16.30 16.00 16.20 2 M2: 16.25 cm3 1(b)(ii) M1 nNaOH 2 1.00  16.25 / 1000 = 0.01625 M2 nHCl unreacted = 0.01625  250 / 25 = 0.1625 1(b)(iii) M1 nHCl reacted 3 [2.00  100 / 1000] – 0.1625 = 0.0375 M2 nCaCO reacted 3 = 0.0375 / 2 = 0.01875 and mass CaCO reacted 3 = 0.01875  100.1 = 1.876875g M3 %CaCO = [1.876875/2.136]  100 3 = 87.9 % 1(c) (25cm3) volumetric pipette 1 1(d) ((2 x 0.0005) / 2.136)  100 (= 0.0468%) 1 1(e) the % by mass (of CaCO in eggshell sample) would be less (than the true value) 1 3 and the (measured) mass (of eggshell) would be greater (than the true value) © UCLES 2022 Page 5 of 7 1(f) volume of NaOH would be 162.5 cm3 1 (which is too large for a 50 cm3 burette) Question Answer Marks

2(a) M1 13 points plotted correctly 2 M2 line of best fit drawn 2(b)(i) (likely to be) point at 18 minutes. 1 2(b)(ii) diameter measured too early 1 or the recorded / measured diameter is smaller than the actual diameter (for that reading 2(c) M1: tangent drawn at t = 15 minutes 3 M2 co-ordinates read and recorded correctly M3 ignore candidate’s response, award 1 mark to all candidates for M3 2(d) average rate of diffusion = (3.6 / 30) 1 = 0.12 cm minutes-1 2(e) time 1 2(f) repeat the experiment to show the points / results / readings are reproducible 1 2(g)(i) Gradient comment 2 M1: lower gradient for K Cr O (than KMnO ) 2 2 7 4 Rate of diffusion + Mr comment M2: diffusion would occur more slowly for K Cr O 2 2 7 and the M is greater r 2(g)(ii) concentration (of solution / s) 1 © UCLES 2022 Page 6 of 7 2(h)(i) (wear) chemically resistant gloves 1 2(h)(ii) any two from: 2 Rate of diffusion solids diffuse too slowly (through the gel) Insolubility solid crystals may not dissolve into gel Uniformity / size of crystals the crystals are not of uniform size © UCLES 2022 Page 7 of 7

1(a)(i) (no. moles of AgCl formed = 3.63 / 143.4 1 = 0.02531381) no. moles MgCl in the sample = 0.02531381 / 2 2 = 0.0126569 answer to at least 2SF 1(a)(ii) M1: mass of MgCl = answer to (a)(i)  95.3 1 2 (= 1.2062 g) M2: % by mass = (M1 /1.52)  100 = (79.355%) 1 answer to at least 2SF 1(b)(i) stir (when solid is mixed with water) 1 OR increase temperature (of water) OR increase state of division of the (solid) mixture 1(b)(ii) to remove magnesium nitrate / (excess) silver nitrate (from the precipitate before drying) 1 1(b)(iii) (It is dried in an oven) to avoid (thermal) decomposition (of silver chloride / precipitate / solid) 1 1(c)(i) ((2  0.005) / 1.52)  100 (= 0.66%) (0.6578947) 1 correct working must be shown along with correct answer. answer to at least 1SF 1(c)(ii) use a larger mass of solid (mixture). 1 1(c)(iii) (continue drying and) reweigh until mass remains constant 1 © UCLES 2022 Page 5 of 8 1(d) the (measured) mass / amount (of ‘AgCl ’ / solid / precipitate) would be greater (than the true value) 1 AND the % by mass (of MgCl in the sample) would be greater (than the true value) 2 Question Answer Marks

2(a) (wear) chemically resistant gloves. 1 2(b)(i) M1 leakproof apparatus capable of delivering a sample of gas (for collection over water) 1 M2: a suitable collection vessel filled with water correctly positioned in a water containing trough to collect the gas (via 1 delivery tube) 2(b)(ii) do not collect the first gas to be delivered 1 © UCLES 2022 Page 6 of 8 2(c)(i) M1: all points plotted correctly 1 M2: line of best fit drawn 1 2(c)(ii) M1: two acceptable coordinates from LOBF expressed in the form (x,y) 1 M2: gradient correctly calculated from points listed for M1 1 (≈ 0.357 cm3 K–1) answer correctly rounded to 3SF 2(d)(i) ring drawn around point at 308 K and 88 cm3 1 2(d)(ii) the (actual) temperature was higher than the recorded / measured temperature / 308K / 35 °C 1 2(e)(i) (absolute) temperature (of the gas) 1 2(e)(ii) more (repeated) measurements should be taken 1 AND anomalies identified / eliminated 2(f) gradient is smaller / line is less steep (for smaller volume of oxygen at start of experiment) 1 AND gradient = nR/P © UCLES 2022 Page 7 of 8

3(a)(i) description of a (clock) method to measure the time taken for a particular amount of product (Br ) to be produced 1 2 3(a)(ii) X = 1, Y = 1 and Z = 2 2 all 3 correct = ✓✓ 2 correct = ✓ 1 or 0 correct = × 3(b) burette 1 3(c) (changing) the temperature (of the reagents) will affect the rate of reaction (so it must be kept constant) 1 3(d) M1: measure (a volume of) 1 moldm-3 sulfuric acid using a burette into a volumetric flask 1 AND make up to the (calibration) mark with distilled water M2: (0.15  a) cm3 of 1 mol dm-3 sulfuric acid is measured to make up a cm3 (of the diluted solution) 1 © UCLES 2022 Page 8 of 8

1(a)(i) All titres to nearest 0.05 cm3 (10.50, 9.65, 9.90, 9.75) 1 1(a)(ii) (9.65 + 9.75) ÷ 2 = 9.70 (cm3) 1 1(b) A solution of known concentration 1 1(c)(i) To allow to reach equilibrium 1 1(c)(ii) To allow solid to settle 1 1(d) Acid is in excess 1 1(e) aqueous potassium manganate(VII) 1 1(f) From colourless to pale pink 1 1(g) Lower percentage error 1 1(h)(i) M1 Mol MnO –(aq) 2 4 = 0.0200  21.10 / 1000 = 4.22  10–4 mol M2 Mol Fe2+(aq) = M1  5 = 2.11  10–3 mol AND Concentration Fe2+(aq) = mol Fe2+  1000 / 25 = 0.0844 mol dm–3 1(h)(ii) Same as [Fe2+(aq)] 1 eqm 1(h)(iii) 0.100 – 0.0844 = 0.0156 1 1(h)(iv) M1 K = 0.0156 / (0.0844  0.0844) = 2.19 2 c M2 dm3 mol–1 © UCLES 2023 Page 5 of 8

2(a) (not all) reactants may feature in the rate determining step 1 OR order can only be determined experimentally 2(b) M1 Dissolve the solid / potassium iodide (in the beaker) (using a small volume of) (distilled) water 3 M2 Transfer / add to a (250 cm3 volumetric) flask AND Rinse (with distilled water) M3 Top the 250 cm3 volumetric flask up to mark (with distilled water) 2(c)(i) Repeat the experiment to show the results are reproducible. 1 2(c)(ii) Volume of KI 1 2(c)(iii) Step 4 1 © UCLES 2023 Page 6 of 8 2(d)(i) 2 Log V Log(1 / t) 0.699 –2.41 1.00 –2.08 1.10 –2.05 1.18 -1.88 X X 1.30 –1.75 1.40 –1.64 M1 Log V Correct values to 3 SF M2 log(1 / t) Correct values to 3 SF 2(d)(ii) M1 6 points plotted correctly 2 M2 Line of best fit drawn 2(d)(iii) Point at log V = 1.10 1 and (recorded time is too high because) watch started too early or stopped too late 2(d)(iv) M1 Co-ordinates read and recorded correctly 2 M2 Gradient calculated to 2 decimal places © UCLES 2023 Page 7 of 8 2(d)(v) percentage error of experimental value 1 = (2(d)(iv) – 1.00) / 1.00]  100 (assuming 2(d)(iv) is 1.10) = [(1.10 – 1.00) / 1.00]  100 = 10% (10% > maximum percentage error / 5.25% ) AND other factors (beyond measurement caused the error) © UCLES 2023 Page 8 of 8

1(a)(i) aqueous AND water has greater density (than ethoxyethane so it forms the lower layer) 1 1(a)(ii) (10 cm3) (volumetric) pipette 1 1(a)(iii) the acid transfers / dissolves into the water (before titration / reaction with sodium hydroxide) 1 1(b)(i) 27.25 1 n (NaOH) in titre = 0.5 (= 0.0136250) 1000 n(HOOCCH CH COOH(aq)) = 0.0136250 / 2 = 0.0068125 2 2 27.25   1000 [HOOCCH 2 CH 2 COOH(aq)] =  0.5  2  = 0.6813 mol dm–3 (0.68125 mol dm–3)  1000   10 at least 2 significant figures 1(b)(ii) M1 [HOOCCH CH COOH(ethoxyethane)] = 0.1125 mol dm–3 2 2 2 (22.50  0.1 / 1000 ÷ 10 / 1000) / 2) M2 K = M1 / (b)(i) pc Expected answer = 0.1125 / 0.68125 = 0.165(1376) (0.1614–0.1662) at least 2 significant figures 1(b)(iii) it is not possible to pipette all (30 cm3) of the aqueous layer from the beaker (as some will always be left behind) 1 1(b)(iv) use a larger volume (>30cm3) of water (in step 1) 1 1(b)(v) K value would be smaller / decrease 1 pc AND because (equilibrium had not been attained and) more butanedioic acid remains in aqueous layer © UCLES 2023 Page 5 of 8

2(a) the application of the hydrolysed samples (to the paper) is more controlled 1 2(b) to make the amino acids / spots visible 1 2(c) lysine, tryptophan and leucine 2 two correct for one mark, three correct for two marks 2(d) two (of the three) amino acids (that compose the tripeptide) are the same 1 2(e)(i) (the spots of two amino acids) have similar (not the same) R values 1 f 2(e)(ii) use a longer stationary phase / (chromatography) paper 1 OR use a different solvent / mobile phase © UCLES 2023 Page 6 of 8

3(a) M1 add (a small volume of) distilled water (to the 50 cm3 beaker) 3 AND dissolve the (aromatic diazonium) compound / solid M2 transfer the solution and washings (using a funnel) AND into a 100 cm3 volumetric flask M3 make up to the (calibration) mark / line with (distilled) water AND then mix the solution (by inverting the flask) 3(b)(i) thermostatically controlled water bath 1 3(b)(ii) volume of (nitrogen) gas (produced) 1 3(b)(iii) not possible to weigh apparatus (while temperature is maintained) in water bath 1 3(c)(i) 1 time / min volume, V / cm3 V – V / cm3 t final t 0 0.0 57.2 5 17.3 39.9 9 27.0 30.2 16 39.5 17.7 21 42.6 14.6 28 49.0 8.2 36 52.8 4.4 final 57.2 0.0 © UCLES 2023 Page 7 of 8 3(c)(ii) M1 all points plotted correctly 2 M2 smooth curve of best fit line drawn passing close to all points except marked anomaly 3(c)(iii) point most anomalous to the plotted line of best fit circled. 1 3(c)(iv) (for anomalous point above the line of best fit) 1 measurement (of volume) was made before the time recorded in the results table (for anomalous point below the line of best fit) measurement (of volume) was made after the time recorded in the results table 3(c)(v) M1 two sets of co-ordinates from the line of best fit correctly recorded for first t AND second t in the form (x, y) 2 ½ ½ M2 both half-lives correctly calculated from co-ordinates 3(c)(vi) first order AND half-lives are constant (within experimental error) 1 © UCLES 2023 Page 8 of 8

1(a)(i) 1.242 g / 1.08 = 1.15 cm3 1 1(a)(ii) burette 1 1(a)(iii) 1  100 / 1000  40 = 4.0(0) g 1 1(b) M1 dissolve the solid / sodium hydroxide (in the beaker) (using a small volume of) (distilled) water 3 M2 transfer / add to a (100 cm3 volumetric) flask AND rinse (with distilled water) M3 top the 100 cm3 volumetric flask up to mark (with distilled water) 1(c) M1 mol C H COOCH = 1.242 / 136 = 0.00913 AND mol of NaOH = 0.100  (10 / 1000) = 0.001(00) 2 6 5 3 M2 mass of benzoic acid decreases AND NaOH no longer in excess / NaOH (now) the limiting (reagent) / not all C H COOCH reacts / statement that mol NaOH < mol ester 6 5 3 1(d)(i) allows heating to increase the rate of reaction without the loss of volatile substances 1 1(d)(ii) (substances) are flammable 1 1(d)(iii) to remove the anti-bumping granules (from the reaction mixture) 1 1(e)(i) add (a little) (named) (acid–base) indicator AND the reaction mixture shows the colour for a (strong) acid in that indicator 1 1(e)(ii) precipitate forms 1 1(f) benzoic acid is less soluble in cold water 1 1(g) dry the precipitate and reweigh until constant mass 1 1(h)(i) 1.242  122 / 136 = 1.11 1 1(h)(ii) 74.0(%) 1 Question Answer Marks

2(a)(i) 1.995  10–7 (mol dm–3) or 2.00  10–7 (mol dm–3) 1 © UCLES 2023 Page 6 of 7 2(a)(ii) 3.98  10–14 (mol2 dm–6) 1 2(a)(iii) as temperature increases K increases 1 w 2(b)(i) M1 1/T all correct to 3 significant figures AND standard form 2 M2 log K all correct to 2 decimal places w T 1 / T K log K w w 283 3.53  10–3 2.93  10–15 – 14.53 293 3.41  10–3 6.81  10–15 – 14.17 303 3.30  10–3 1.47  10–14 – 13.83 313 3.19  10–3 2.92  10–14 – 13.53 323 3.10  10–3 5.48  10–14 – 13.26 333 3.00  10–3 1.09  10–13 – 12.96 343 2.92  10–3 1.45  10–13 – 12.84 2(b)(ii) M1 seven points plotted correctly 2 M2 line of best fit drawn 2(b)(iii) plot at 2.92  10 –3, –12.84 1 2(b)(iv) pH was recorded at a lower temperature than 343 K 1 2(b)(v) M1 co-ordinates read and recorded correctly 2 M2 gradient calculated to three significant figures 2(b)(vi) M1 gradient = –H / 2.303R OR H = –gradient  2.303  8.31 OR any correct rearrangement of this 2 M2 correct calculation of H from 2(b)(v) © UCLES 2023 Page 7 of 7

1(a)(i) aqueous AND water has greater density (than ethoxyethane so it forms the lower layer) 1 1(a)(ii) (10 cm3) (volumetric) pipette 1 1(a)(iii) the acid transfers / dissolves into the water (before titration / reaction with sodium hydroxide) 1 1(b)(i) 27.25 1 n (NaOH) in titre = 0.5 (= 0.0136250) 1000 n(HOOCCH CH COOH(aq)) = 0.0136250 / 2 = 0.0068125 2 2 27.25   1000 [HOOCCH 2 CH 2 COOH(aq)] =  0.5  2  = 0.6813 mol dm–3 (0.68125 mol dm–3)  1000   10 at least 2 significant figures 1(b)(ii) M1 [HOOCCH CH COOH(ethoxyethane)] = 0.1125 mol dm–3 2 2 2 (22.50  0.1 / 1000 ÷ 10 / 1000) / 2) M2 K = M1 / (b)(i) pc Expected answer = 0.1125 / 0.68125 = 0.165(1376) (0.1614–0.1662) at least 2 significant figures 1(b)(iii) it is not possible to pipette all (30 cm3) of the aqueous layer from the beaker (as some will always be left behind) 1 1(b)(iv) use a larger volume (>30cm3) of water (in step 1) 1 1(b)(v) K value would be smaller / decrease 1 pc AND because (equilibrium had not been attained and) more butanedioic acid remains in aqueous layer © UCLES 2023 Page 5 of 8

2(a) the application of the hydrolysed samples (to the paper) is more controlled 1 2(b) to make the amino acids / spots visible 1 2(c) lysine, tryptophan and leucine 2 two correct for one mark, three correct for two marks 2(d) two (of the three) amino acids (that compose the tripeptide) are the same 1 2(e)(i) (the spots of two amino acids) have similar (not the same) R values 1 f 2(e)(ii) use a longer stationary phase / (chromatography) paper 1 OR use a different solvent / mobile phase © UCLES 2023 Page 6 of 8

3(a) M1 add (a small volume of) distilled water (to the 50 cm3 beaker) 3 AND dissolve the (aromatic diazonium) compound / solid M2 transfer the solution and washings (using a funnel) AND into a 100 cm3 volumetric flask M3 make up to the (calibration) mark / line with (distilled) water AND then mix the solution (by inverting the flask) 3(b)(i) thermostatically controlled water bath 1 3(b)(ii) volume of (nitrogen) gas (produced) 1 3(b)(iii) not possible to weigh apparatus (while temperature is maintained) in water bath 1 3(c)(i) 1 time / min volume, V / cm3 V – V / cm3 t final t 0 0.0 57.2 5 17.3 39.9 9 27.0 30.2 16 39.5 17.7 21 42.6 14.6 28 49.0 8.2 36 52.8 4.4 final 57.2 0.0 © UCLES 2023 Page 7 of 8 3(c)(ii) M1 all points plotted correctly 2 M2 smooth curve of best fit line drawn passing close to all points except marked anomaly 3(c)(iii) point most anomalous to the plotted line of best fit circled. 1 3(c)(iv) (for anomalous point above the line of best fit) 1 measurement (of volume) was made before the time recorded in the results table (for anomalous point below the line of best fit) measurement (of volume) was made after the time recorded in the results table 3(c)(v) M1 two sets of co-ordinates from the line of best fit correctly recorded for first t AND second t in the form (x, y) 2 ½ ½ M2 both half-lives correctly calculated from co-ordinates 3(c)(vi) first order AND half-lives are constant (within experimental error) 1 © UCLES 2023 Page 8 of 8

1(a)(i) M1: 27.30, 27.00, 26.70, 26.80 2 M2: correct averaging of two (or more) titres within 0.10 cm3 of each other. (Expected answer = (26.70 + 26.80) / 2 = 26.75) 1(a)(ii) M1: n(Na S O (aq)) = (a(i) / 1000)  0.001 3 2 2 3 (Expected answer = 26.75 / 1000 x 0.001 = 2.675  10-5) M2: n(O (aq)) = M1 / 4 2 (Expected answer = 2.675  10-5 / 4 = 6.6875 x 10-6) M3: concentration of oxygen = M2  1000 / 25 = M2 x 40 (Expected answer = 6.6875  10-6  1000 / 25 = 2.675  10-4 mol dm-3) Answer to at least 3SF 1(b) (25.0 cm3) volumetric pipette 1 1(c) to avoid any oxygen from (trapped) air (in the flask) reacting with / oxidising Mn(OH) 1 2 1(d)(i) M1: All points plotted correctly. 2 M2: smooth curve LOBF drawn. 1(d)(ii) Correct value read from candidate’s graph. 1 Value given to at least 3SF. (Expected value – 2.57  10-4 moldm-3) © UCLES 2023 Page 8 of 11 1(d)(iii) M1 Point most anomalous to the plotted line of best fit circled. 2 M2: For anomalous point below the LOBF The (actual) temperature > recorded / measured temperature (in the table). For anomalous point above the LOBF. The (actual) temperature < recorded / measured temperature (in the table). Question Answer Marks

2(a) M1: Leakproof reaction vessel capable of delivering a sample of gas. 3 M2: Suitable method of collection and measurement of the gas produced. (eg. over water or gas syringe). M3: method for monitoring & maintaining temperature (thermostatically controlled water bath). 2(b)(i) M1: A tangent line which is… 2 • a straight line • starts at / passes through 0,0. • keeps to the left of the curve of the original line. • covers at least 25 cm3 (5 big squares) on y-axis. • passes between 4.0 and 5.5 minutes (inc.) at 25 cm3 M2: correct calculation of the gradient of tangent line drawn. 2(b)(ii) The total volume of gas produced divided by the time taken is the mean rate (rather than the initial rate). 1 2(b)(iii) It (the line / curve) would be below / lower (than the one on the graph) (starting at 0,0). 1 © UCLES 2023 Page 9 of 11 2(b)(iv) A second curve which: 1 • starts at 0,0 (± 1 small square) • is less steep than curve for 0.0750 moldm-3. (before any plateau) • produces 27.5 cm3 gas in total by 45 minutes. (± half a small square). • Extends from 0 – 45 minutes. 2(c)(i) 1 concentration rate 0.5 0.000714 7.14 10-4 0.4 0.000455 4.55 10-4 0.3 0.000313 3.13 10-4 0.2 0.000234 2.34 10-4 0.1 0.000123 1.23 10-4 2(c)(ii) explanation using numbers from the table that whatever change is made to the concentration causes the same change in 1 the rate (within experimental error). 2(c)(iii) time (taken to collect 0.0150dm3 of N ) 1 2 2(c)(iv) M1: Correct volume, 40(.0) cm3, (of 0.5(00) moldm-3 ) C H N Cl(aq) is used / measured. 3 6 5 2 M2: measure the volume from M1 C H N Cl using a (50 cm3) burette into a 100 cm3 volumetric flask. 6 5 2 M3: make up to the (calibration) mark with distilled water. AND then mix the solution (by inverting the flask) 2(c)(v) to make sure the concentration does not change (from 0.200 moldm-3) (by making sure the C H N Cl does not decompose) 1 6 5 2 © UCLES 2023 Page 10 of 11 2(d)(i) Two acceptable reasons for low yield. 2 1 Some C H N Cl had decomposed / reacted with water (before reacting with phenylamine) OR temperature rose above 6 5 2 5 oC (in step 1) OR phenylamine used was impure. 2 Some dye / solid is not recovered / is lost through / left in filter OR some of the dye dissolves in the water / is aqueous (in step 2). 2(d)(ii) (Residual) water causes solid to have a different / inaccurate (lower) melting point (to the dry solid). 1 OR To ensure all water has been driven off to increase accuracy in measurement of melting point © UCLES 2023 Page 11 of 11

1(a)(i) 9 points plotted correctly 2 Two straight lines of best fit which correctly intersect 1(a)(ii) Temperature change = 1 intersection point temperature (read from graph) – 18.8 1(a)(iii) intersection point volume (read from graph) 1 1(a)(iv) n(HCl) = 1.00  (25.00/1000) = 0.0250 1 [NaOH] = 0.0250  (1000/1(a)(iii)) 1 1(a)(v) The indicator: 1 changes colour rapidly / instantly OR detects end-point / neutralisation rapidly / instantly 1(b) (25 cm3) Volumetric pipette 1 1(c) ((2  0.1)/2.5)  100 = 8(.00) (%) 1 1(d) mcΔT = 1 (25.00 + 22.10)  4.18 x 6.0 = 1181.268 (J) = q/n(NaOH) (÷1000) 1 = 1181.268 / (1.00  22.10/1000) ÷ 1000 = – 53.5 (kJ mol–1) 1(e) Heat loss (to the surroundings) 1 1(f) Ethanoic acid is a weak acid 2 Energy is required for dissociation of ethanoic acid © UCLES 2023 Page 5 of 7

2(a) Contents of flask 3 Sealed apparatus Collection of the gas in a labelled suitable container 2(b) 12.5(0) cm3 (of 2.00 mol dm–3) HCl 3 Using burette transfer and add to a volumetric flask Top the (volumetric) flask up to 250 cm3 mark with distilled water 2(b) 12.5(0) cm3 (of 2.00 mol dm–3) HCl Using burette transfer and add to a volumetric flask Top the (volumetric) flask up to 250 cm3 mark with distilled water 2(c)(i) (The more concentrated) HCl is corrosive 1 OR (The more concentrated) HCl is an irritant 2(c)(ii) 1 2.00 15.82 0.0640 3.00 10.41 0.0961 4.00 7.81 0.128 5.00 6.25 0.160 6.00 5.24 0.191 2(c)(iii) Straight line going through the origin with a positive gradient 1 2(c)(iv) Straight line labelled B passing through the origin but with steeper gradient than line A 1 © UCLES 2023 Page 6 of 7 2(c)(v) Rate = k [HCl] 1 2(d)(i) (at higher concentrations) line curves (upwards) 2 Rate (1/t) increases as temperature increases 2(d)(ii) Use a water bath 1 2(e)(i) (remove oxide layer) by using sandpaper 1 2(e)(ii) (zinc oxide + acid) doesn’t produce hydrogen (at the start) 1 © UCLES 2023 Page 7 of 7

1(a)(i) M1: 27.30, 27.00, 26.70, 26.80 2 M2: correct averaging of two (or more) titres within 0.10 cm3 of each other. (Expected answer = (26.70 + 26.80) / 2 = 26.75) 1(a)(ii) M1: n(Na S O (aq)) = (a(i) / 1000)  0.001 3 2 2 3 (Expected answer = 26.75 / 1000 x 0.001 = 2.675  10-5) M2: n(O (aq)) = M1 / 4 2 (Expected answer = 2.675  10-5 / 4 = 6.6875 x 10-6) M3: concentration of oxygen = M2  1000 / 25 = M2 x 40 (Expected answer = 6.6875  10-6  1000 / 25 = 2.675  10-4 mol dm-3) Answer to at least 3SF 1(b) (25.0 cm3) volumetric pipette 1 1(c) to avoid any oxygen from (trapped) air (in the flask) reacting with / oxidising Mn(OH) 1 2 1(d)(i) M1: All points plotted correctly. 2 M2: smooth curve LOBF drawn. 1(d)(ii) Correct value read from candidate’s graph. 1 Value given to at least 3SF. (Expected value – 2.57  10-4 moldm-3) © UCLES 2023 Page 8 of 11 1(d)(iii) M1 Point most anomalous to the plotted line of best fit circled. 2 M2: For anomalous point below the LOBF The (actual) temperature > recorded / measured temperature (in the table). For anomalous point above the LOBF. The (actual) temperature < recorded / measured temperature (in the table). Question Answer Marks

2(a) M1: Leakproof reaction vessel capable of delivering a sample of gas. 3 M2: Suitable method of collection and measurement of the gas produced. (eg. over water or gas syringe). M3: method for monitoring & maintaining temperature (thermostatically controlled water bath). 2(b)(i) M1: A tangent line which is… 2 • a straight line • starts at / passes through 0,0. • keeps to the left of the curve of the original line. • covers at least 25 cm3 (5 big squares) on y-axis. • passes between 4.0 and 5.5 minutes (inc.) at 25 cm3 M2: correct calculation of the gradient of tangent line drawn. 2(b)(ii) The total volume of gas produced divided by the time taken is the mean rate (rather than the initial rate). 1 2(b)(iii) It (the line / curve) would be below / lower (than the one on the graph) (starting at 0,0). 1 © UCLES 2023 Page 9 of 11 2(b)(iv) A second curve which: 1 • starts at 0,0 (± 1 small square) • is less steep than curve for 0.0750 moldm-3. (before any plateau) • produces 27.5 cm3 gas in total by 45 minutes. (± half a small square). • Extends from 0 – 45 minutes. 2(c)(i) 1 concentration rate 0.5 0.000714 7.14 10-4 0.4 0.000455 4.55 10-4 0.3 0.000313 3.13 10-4 0.2 0.000234 2.34 10-4 0.1 0.000123 1.23 10-4 2(c)(ii) explanation using numbers from the table that whatever change is made to the concentration causes the same change in 1 the rate (within experimental error). 2(c)(iii) time (taken to collect 0.0150dm3 of N ) 1 2 2(c)(iv) M1: Correct volume, 40(.0) cm3, (of 0.5(00) moldm-3 ) C H N Cl(aq) is used / measured. 3 6 5 2 M2: measure the volume from M1 C H N Cl using a (50 cm3) burette into a 100 cm3 volumetric flask. 6 5 2 M3: make up to the (calibration) mark with distilled water. AND then mix the solution (by inverting the flask) 2(c)(v) to make sure the concentration does not change (from 0.200 moldm-3) (by making sure the C H N Cl does not decompose) 1 6 5 2 © UCLES 2023 Page 10 of 11 2(d)(i) Two acceptable reasons for low yield. 2 1 Some C H N Cl had decomposed / reacted with water (before reacting with phenylamine) OR temperature rose above 6 5 2 5 oC (in step 1) OR phenylamine used was impure. 2 Some dye / solid is not recovered / is lost through / left in filter OR some of the dye dissolves in the water / is aqueous (in step 2). 2(d)(ii) (Residual) water causes solid to have a different / inaccurate (lower) melting point (to the dry solid). 1 OR To ensure all water has been driven off to increase accuracy in measurement of melting point © UCLES 2023 Page 11 of 11

1(a) M1 Order of weighing 2 • 1 boat + AgNO is weighed 3 • 2 (AgNO transferred) 3 • 3 empty boat reweighed M2 table + units / g Mass of boat + AgNO before 3 transfer Mass of boat after transfer Mass of AgNO transferred 3 1(b) M1 Dissolve the solid / silver nitrate (in the beaker) (using a small volume of) (distilled) water 3 M2 Transfer / add to a (250 cm3 volumetric) flask and Rinse (with distilled water) M3 Top the 250 cm3 volumetric flask up to mark (with distilled water) 1(c) Sunlight decomposes silver nitrate 1 1(d) Filter 1 1(e)(i) (10 cm3) (volumetric) pipette 1 1(e)(ii) Dropping pipette 1 (as 1 cm3, not 1.00 cm3 is asked for) 1(f) Wear chemically resistant gloves 1 1(g) Solution X 1 © Cambridge University Press & Assessment 2024 Page 5 of 8 1(h)(i) 23.40; 22.35; 22.60; 22.45 1 1(h)(ii) (22.35 + 22.45) ÷ 2 = 22.40 (cm3) 1 1(h)(iii) M1 Mol AgNO used = 10.62 / 169.9 = 0.0625… (mol) 3 3 M2 Mol Ag+(aq) reacting with Cl–(aq) = M1  22.40/250 = 5.60  10–3 (mol) M3 Conc Cl –(aq) = M2  1000 / 10 = 0.560 (mol dm–3) 1(h)(iv) [(0.05  2) / 22.60]  100 = 0.442% 1 Working must be shown 1(i) Ag+ ions react with other substances in the sample of sea water 1 Question Answer Marks

2(a) Step 3 1 2(b) M1 Lowers the temperature (of reaction mixture) 2 M2 Decreases concentration (in reaction mixture) © Cambridge University Press & Assessment 2024 Page 6 of 8 2(c)(i) M1 Column 4 M2 Column 5 2 1 2 3 4 5 V t (V ∞ – V t ) / cm3 / cm3 1 1 12.60 1.20 13.30 2 13 17.70 6.30 8.20 3 20 19.90 8.50 6.00 4 30 22.10 10.70 3.80 5 40 6 50 24.90 13.50 1.00 7 60 25.90 14.50 0.00 2(c)(ii) Time 1 2(c)(iii) Temperature (of flask B) 1 2(c)(iv) Yes 1 and The value of the titre is accurate and corresponds to correct time 2(c)(v) M1 6 points plotted correctly 2 M2 Line of best fit drawn © Cambridge University Press & Assessment 2024 Page 7 of 8 2(c)(vi) 25.90 – (V – V) at 40 minutes from the graph 1 ∞ 2(c)(vii) No and there is an anomalous point on the graph 1 or Yes and all the points lie on/close to the line of best fit © Cambridge University Press & Assessment 2024 Page 8 of 8

1(a)(i) 0.248(2) (g) 1 1(a)(ii) (500 cm3) volumetric flask 1 1(b)(i) 20.5 1 100 = 20(.0%) 5.0 correct working must be shown 1(b)(ii) 1 greater no effect smaller uncertainty of the  measurement percentage error of the  measurement 1(c)(i) M1 rinse / wash (50 cm3 burette) with (0.0200 mol dm–3 aqueous) sodium thiosulfate (before filling with aqueous sodium 2 thiosulfate) M2 place (aqueous) sodium thiosulfate in the burette (to fill) AND then run some solution out (through the jet) (by opening the tap) 1(b)(ii) M1 2  add / run Na S O (aq) (into the conical flask) 2 2 3  until (permanent) colour change (seen) / end-point reached M2 add dropwise (towards the end) (to ensure the end-point is accurate) 1(d) to ensure the reaction(s) is / are complete (in the syringe) 1 © Cambridge University Press & Assessment 2024 Page 5 of 7 1(e) 2 (titration) A (titration) B (titration) C (titration) D (titration) E final (burette) reading / cm3 initial (burette) reading / cm3 titre / cm3 M1 headings and units correct for table  initial / start and (burette) reading / volume  final / end and (burette) reading / volume  titre or volume / (0.002(00) mol dm–3) sodium thiosulfate (solution) and used / added  units: (cm3) or / cm3 or in cm3 for all headings M2 five columns for syringes A–E 1(f) M1 n(Na S O ) = 12.65 / 1000  0.00200 = 2.53  10–5 2 2 2 3 M2 n(O ) = M1 / 4 = (2.53  10–5 / 4 = 6.325  10–6 mol) 2 concentration of O = (M1 / 4)  1000 / 30 (= 2.10833  10–4 mol dm–3) (= 2.11  10–4 mol dm–3) 2 1(g)(i) there was (a small amount of dissolved) oxygen in the other solutions / reagents / reactants (used in the experiment) 1 1(g)(ii) subtract the result (2.26  10–5 mol dm–3) of the distilled water experiment from the final result for dissolved oxygen in 1(f) 1 1(h) chlorine is an oxidising agent 1 OR chlorine reacts in the same way as oxygen OR chlorine reacts with Mn2+ / S O 2– / I– / reactant(s) 2 3 Question Answer Marks

2(a) To ensure the solution(s) (in flasks A and B) are at the same temperature (of the water bath) (before mixing) 1 © Cambridge University Press & Assessment 2024 Page 6 of 7 2(b)(i) (take the temperature of reaction mixture in flask A) 1 1 at the start of reaction / step 7 OR (immediately) before step 7 OR step 6 / (immediately) before the reaction OR (immediately) after step 5 AND 2 at the end of reaction / step 8 / when cross is no longer visible / (immediately) after step 8 2(b)(ii) calculate the mean (temperature during the reaction) 1 2(c) 2 temperature, T / C time, t / s temperature, T / K 1 / t / s–1 15 176 288 0.0057 24 92 297 0.0109 39 62 305 0.0161 M1 column 3 correct M2 column 4 correct 2(d)(i) M1 all points plotted correctly 2 M2 straight line of best fit line drawn passing close to all points (except marked anomaly) 2(d)(ii) M1 two acceptable coordinates from line if best fit expressed in the form (x,y) 2 M2 gradient correctly calculated from points listed for M1 answer correctly rounded to three significant figures 2(d)(iii) M1 any correct version of the equation: gradient = – 0.434 x E / R 3 A M2 evaluation of expression to give value for E A M3 units = kJ mol–1 2(d)(iv) yes, there are no / few anomalous points / most points lie on or near the line (of best fit) 1 OR no, there is an anomalous point(s) / (some) points don’t lie on or near the line (of best fit) 2(e) increase the concentration of one or both of the reactants 1 © Cambridge University Press & Assessment 2024 Page 7 of 7

1(a) you cannot (easily) measure temperature (change) whilst applying heat 1 1(b)(i) 5.01 g 1 1(b)(ii) M1 order of weighing: 2 1 weighing boat + CaCO is weighed 3 (CaCO added to beaker containing HCl) 3 2 weighing boat is weighed after CaCO is added to HCl 3 M2 table + units: / g 1 mass of boat + CaCO (before transfer) 3 2 mass of boat (+ residue of CaCO ) (after addition) 3 mass of CaCO added 3 1(c) burette AND burette measures to nearest 0.05 cm3 1 1(d) stir the solution / mixture 1 1(e)(i) M1 10 points plotted correctly from t = 3.5 mins to t = 8 mins 2 M2 line of best fit drawn involving points from 4 to 8 minutes AND extrapolated back to 3 minutes 1(e)(ii) 38.5 – 19.0 = 19.5 C 1 1(f) the reaction is not complete (at 3.5 minutes) 1 1(g) M1 q = 50 g x 4.18 J g–1 K–1 x 6 K = 12958 J 2 M2 H = M1 / 0.0500 = 12 958 J / 0.0500 mol = 259 160 J mol–1 = –259 kJ mol–1 2 1(h) ∆H = ∆H – ∆H = –84 – (–259) = (+)175 (kJ mol–1) 1 r 1 2 © Cambridge University Press & Assessment 2024 Page 5 of 6 1(i) M1 weakness: heat loss to the surroundings 2 M2 improvement: use a lid Question Answer Marks

2(a) M1 volume of solution A = 21.75 cm3 (to nearest 0.05 cm3) 3 M2 use burette to transfer 21.75 cm3 of solution A and add to a volumetric flask M3 top the (100 cm3 volumetric) flask up to 100 cm3 mark with distilled water 2(b) so that concentration of [Fe(SCN)2+] is known (as all solution B / SCN– reacts) 1 2(c)(i) (relative) absorbance 1 2(c)(ii) add ice (to the water in the beaker) 1 2(d)(i) 8.9 and 6.2 in column 3 1 2(d)(ii) 107 and 70 in column 4 1 2(e)(i) the graph is a straight line 1 2(e)(ii) M1 anomalous point ringed 2 M2 not all solution B was transferred / added (in step 5) (making concentration of FeSCN2+ too low) 2(e)(iii) M1 co-ordinates read and recorded correctly 2 M2 gradient calculated to three significant figures 2(e)(iv) M1 gradient / 2(e)(iii) = –∆H / 2.303R OR any correct rearrangement of this e.g. ∆H = gradient / 2(e)(iii)  –2.303  8.31 2 M2 correct calculations of ∆H including conversion to kJ © Cambridge University Press & Assessment 2024 Page 6 of 6

1(a)(i) 0.248(2) (g) 1 1(a)(ii) (500 cm3) volumetric flask 1 1(b)(i) 20.5 1 100 = 20(.0%) 5.0 correct working must be shown 1(b)(ii) 1 greater no effect smaller uncertainty of the  measurement percentage error of the  measurement 1(c)(i) M1 rinse / wash (50 cm3 burette) with (0.0200 mol dm–3 aqueous) sodium thiosulfate (before filling with aqueous sodium 2 thiosulfate) M2 place (aqueous) sodium thiosulfate in the burette (to fill) AND then run some solution out (through the jet) (by opening the tap) 1(b)(ii) M1 2  add / run Na S O (aq) (into the conical flask) 2 2 3  until (permanent) colour change (seen) / end-point reached M2 add dropwise (towards the end) (to ensure the end-point is accurate) 1(d) to ensure the reaction(s) is / are complete (in the syringe) 1 © Cambridge University Press & Assessment 2024 Page 5 of 7 1(e) 2 (titration) A (titration) B (titration) C (titration) D (titration) E final (burette) reading / cm3 initial (burette) reading / cm3 titre / cm3 M1 headings and units correct for table  initial / start and (burette) reading / volume  final / end and (burette) reading / volume  titre or volume / (0.002(00) mol dm–3) sodium thiosulfate (solution) and used / added  units: (cm3) or / cm3 or in cm3 for all headings M2 five columns for syringes A–E 1(f) M1 n(Na S O ) = 12.65 / 1000  0.00200 = 2.53  10–5 2 2 2 3 M2 n(O ) = M1 / 4 = (2.53  10–5 / 4 = 6.325  10–6 mol) 2 concentration of O = (M1 / 4)  1000 / 30 (= 2.10833  10–4 mol dm–3) (= 2.11  10–4 mol dm–3) 2 1(g)(i) there was (a small amount of dissolved) oxygen in the other solutions / reagents / reactants (used in the experiment) 1 1(g)(ii) subtract the result (2.26  10–5 mol dm–3) of the distilled water experiment from the final result for dissolved oxygen in 1(f) 1 1(h) chlorine is an oxidising agent 1 OR chlorine reacts in the same way as oxygen OR chlorine reacts with Mn2+ / S O 2– / I– / reactant(s) 2 3 Question Answer Marks

2(a) To ensure the solution(s) (in flasks A and B) are at the same temperature (of the water bath) (before mixing) 1 © Cambridge University Press & Assessment 2024 Page 6 of 7 2(b)(i) (take the temperature of reaction mixture in flask A) 1 1 at the start of reaction / step 7 OR (immediately) before step 7 OR step 6 / (immediately) before the reaction OR (immediately) after step 5 AND 2 at the end of reaction / step 8 / when cross is no longer visible / (immediately) after step 8 2(b)(ii) calculate the mean (temperature during the reaction) 1 2(c) 2 temperature, T / C time, t / s temperature, T / K 1 / t / s–1 15 176 288 0.0057 24 92 297 0.0109 39 62 305 0.0161 M1 column 3 correct M2 column 4 correct 2(d)(i) M1 all points plotted correctly 2 M2 straight line of best fit line drawn passing close to all points (except marked anomaly) 2(d)(ii) M1 two acceptable coordinates from line if best fit expressed in the form (x,y) 2 M2 gradient correctly calculated from points listed for M1 answer correctly rounded to three significant figures 2(d)(iii) M1 any correct version of the equation: gradient = – 0.434 x E / R 3 A M2 evaluation of expression to give value for E A M3 units = kJ mol–1 2(d)(iv) yes, there are no / few anomalous points / most points lie on or near the line (of best fit) 1 OR no, there is an anomalous point(s) / (some) points don’t lie on or near the line (of best fit) 2(e) increase the concentration of one or both of the reactants 1 © Cambridge University Press & Assessment 2024 Page 7 of 7

1(a) wear chemically resistant gloves. 1 1(b) M1 Includes the following steps. Measure the mass of.. 2 1 (Weighing) boat + solid 2 (Weighing) boat + residue / residual solid (after transfer) M2 Table and units. Headings must be unambiguous, and correct units must be included for each heading. / g Mass of boat + solid (before transfer) Mass of boat (after transfer) (Mass of) solid (transferred) 1(c) M1 Correctly placed vertical condenser including jacket. 2 M2 (Cold) water in at bottom and water out at the top of the condenser. 1(d)(i) (alkaline aqueous) iodine is in excess. 1 1(d)(ii) to ensure the reaction is complete. 1 © Cambridge University Press & Assessment 2024 Page 4 of 7 1(d)(iii) to remove soluble substances (from the residue / solid C). 1 Acceptable named soluble substances in order of diminishing likelihood to be mentioned • (aqueous alkaline) iodine • Sodium hydroxide • Solution B • Sodium hydrogencarbonate • Sodium iodide • C H O - Na+ 7 5 3 • C H O - Na+ 2 3 2 • Water washable impurities 1(d)(iv) The residue is less soluble in cold water. 1 1(e)(i) amount of (C H I O) = 0.764 / 687.6 = 1.111  10-3 mol 1 6 2 2 2 1(e)(ii) amount of C H O = 2 x 1(e)(i) (=2.222  10-3) 1 9 8 4 mass of aspirin = 2  1(e)(i)  180 (= 0.400 g) 1(e)(iii) percentage aspirin by mass = (1(e)(ii) / 0.409)  100 (= 97.8%) 1 1(f) amount / mass of solid C would be greater (than the true value) 1 AND calculated percentage by mass would be greater than (e)(iii) Question Answer Marks

2(a) 588 nm (589.7) 1 2(b)(i) n (C N H Cl(s)) = 2.5  10-2 x 0.5 dm3 = 1.25  10-2 1 25 3 30 mass of C N H Cl(s) = 1.25  10-2  407.5 = 5.09 g 25 3 30 © Cambridge University Press & Assessment 2024 Page 5 of 7 2(b)(ii) M1 add a (small) volume of (distilled) water (to the small beaker) 3 AND dissolve the C N H Cl (s) 25 3 30 M2 Transfer the solution to a 500 cm3 volumetric flask with washings. M3: make up to the (calibration) mark (with distilled water.) AND then mix the solution (by inverting the flask) 2(c)(i) 1 Volume of Volume of 2.5  10-4 moldm-3 distilled crystal violet water / cm3 (solution E) / cm3 0.00 20.00 4.00 16.00 8.00 12.00 12.00 8.00 16.00 4.00 20.00 0.00 2(c)(ii) absorbance (of aqueous C N H Cl) 1 25 3 30 2(d)(i) M1 points plotted correctly. 2 M2 Straight line of best fit drawn. © Cambridge University Press & Assessment 2024 Page 6 of 7 2(d)(ii) M1 Most anomalous point circled. 2 (Expected to be concentration 1.0  10-4 moldm-3 (solution 3) M2 Volume of water added (to mixture) too large OR Volume of crystal violet solution / solution E added (to mixture) too small. 2(d)(iii) (absorbance is) (directly) proportional (to concentration of crystal violet) (within experimental error). 1 2(d)(iv) Repeat the procedure for the solution giving an anomalous result. (Solution 3) 1 2(e)(i) Solutions being mixed (at t=0) so reading not possible. 1 2(e)(ii) M1 (100, 0.360) and (315, 0.180) 2 M2 half-life correctly calculated from points listed for M1 (x1–x2) when y = 2y 2 1 2(e)(iii) first order 1 AND half-lives are constant (within experimental error) © Cambridge University Press & Assessment 2024 Page 7 of 7

1(a)(i) 13.25 g 1 1(a)(ii) M1 dissolve the solid / sodium carbonate (in the beaker) (using a small volume of) (distilled) water 3 M2 transfer / add to a (250 cm3 volumetric) flask and rinse (with distilled water) M3 top the 250 cm3 volumetric flask up to mark (with distilled water) 1(b)(i) solution Y 1 1(b)(ii) indicator / methyl orange changes colour 1 1(b)(iii) to avoid spitting (of solid when it forms) 1 1(b)(iv) heat to constant mass 1 1(c)(i) 2 burette reading final 14.85 burette reading initial 1.35 volume of solution X 13.50 M1 burette readings 14.85 (cm3) and 1.35 (cm3) M2 volume of solution X added = 13.50 (cm3) 1(c)(ii) 2  0.05 1 working must be shown  100 = 0.741 13.50 © Cambridge University Press & Assessment 2024 Page 5 of 7 1(d) M1 M(NaCl) = 58.5 3 r n(NaCl) = 1.17 g / 58.5 = 0.0200 M2 n(HCl) = 0.02 c(HCl) (X) = 0.02/0.01335 = 1.50 (mol dm–3) M3 n(Na CO ) = 0.02 / 2 = 0.01 2 3 c(Na CO ) (Y) = 0.01 / 0.025 = 0.400 (mol dm–3) 2 3 1(e) M1 calculated concentration of Y will be higher than the true value. 2 M2 mass / amount of NaCl (in step 7) will be too high. Question Answer Marks

2(a)(i) pipeclay triangle 1 2(a)(ii) toxic gas is produced. 1 2(a)(iii) to ensure all of the metal M reacts. 1 2(b) 1 mass of M 1.4 1.1 0.8 0.5 0.2 3 4 6 7 9 mass of S 0.4 0.2 0.2 0.1 0.0 6 8 0 5 6 2(c) mass of M or mass of metal 1 2(d)(i) 5 points plotted correctly from 2(b) 1 straight line of best fit drawn which includes origin 1 © Cambridge University Press & Assessment 2024 Page 6 of 7 2(d)(ii) most anomalous point selected 1 not all of the sulfur had been removed 1 (in step 4) 2(e) co-ordinates correctly recorded from LOBF 2 gradient calculated to three significant figures 2(f) not reliable 1 and there is an anomalous point 2(g)(i) (32.1 / 87.6) = 0.366 1 2(g)(ii) (assuming values in 2(e) and 2(g)(i) are different) 1 not correct and gradient is different © Cambridge University Press & Assessment 2024 Page 7 of 7

1(a) wear chemically resistant gloves. 1 1(b) M1 Includes the following steps. Measure the mass of.. 2 1 (Weighing) boat + solid 2 (Weighing) boat + residue / residual solid (after transfer) M2 Table and units. Headings must be unambiguous, and correct units must be included for each heading. / g Mass of boat + solid (before transfer) Mass of boat (after transfer) (Mass of) solid (transferred) 1(c) M1 Correctly placed vertical condenser including jacket. 2 M2 (Cold) water in at bottom and water out at the top of the condenser. 1(d)(i) (alkaline aqueous) iodine is in excess. 1 1(d)(ii) to ensure the reaction is complete. 1 © Cambridge University Press & Assessment 2024 Page 4 of 7 1(d)(iii) to remove soluble substances (from the residue / solid C). 1 Acceptable named soluble substances in order of diminishing likelihood to be mentioned • (aqueous alkaline) iodine • Sodium hydroxide • Solution B • Sodium hydrogencarbonate • Sodium iodide • C H O - Na+ 7 5 3 • C H O - Na+ 2 3 2 • Water washable impurities 1(d)(iv) The residue is less soluble in cold water. 1 1(e)(i) amount of (C H I O) = 0.764 / 687.6 = 1.111  10-3 mol 1 6 2 2 2 1(e)(ii) amount of C H O = 2 x 1(e)(i) (=2.222  10-3) 1 9 8 4 mass of aspirin = 2  1(e)(i)  180 (= 0.400 g) 1(e)(iii) percentage aspirin by mass = (1(e)(ii) / 0.409)  100 (= 97.8%) 1 1(f) amount / mass of solid C would be greater (than the true value) 1 AND calculated percentage by mass would be greater than (e)(iii) Question Answer Marks

2(a) 588 nm (589.7) 1 2(b)(i) n (C N H Cl(s)) = 2.5  10-2 x 0.5 dm3 = 1.25  10-2 1 25 3 30 mass of C N H Cl(s) = 1.25  10-2  407.5 = 5.09 g 25 3 30 © Cambridge University Press & Assessment 2024 Page 5 of 7 2(b)(ii) M1 add a (small) volume of (distilled) water (to the small beaker) 3 AND dissolve the C N H Cl (s) 25 3 30 M2 Transfer the solution to a 500 cm3 volumetric flask with washings. M3: make up to the (calibration) mark (with distilled water.) AND then mix the solution (by inverting the flask) 2(c)(i) 1 Volume of Volume of 2.5  10-4 moldm-3 distilled crystal violet water / cm3 (solution E) / cm3 0.00 20.00 4.00 16.00 8.00 12.00 12.00 8.00 16.00 4.00 20.00 0.00 2(c)(ii) absorbance (of aqueous C N H Cl) 1 25 3 30 2(d)(i) M1 points plotted correctly. 2 M2 Straight line of best fit drawn. © Cambridge University Press & Assessment 2024 Page 6 of 7 2(d)(ii) M1 Most anomalous point circled. 2 (Expected to be concentration 1.0  10-4 moldm-3 (solution 3) M2 Volume of water added (to mixture) too large OR Volume of crystal violet solution / solution E added (to mixture) too small. 2(d)(iii) (absorbance is) (directly) proportional (to concentration of crystal violet) (within experimental error). 1 2(d)(iv) Repeat the procedure for the solution giving an anomalous result. (Solution 3) 1 2(e)(i) Solutions being mixed (at t=0) so reading not possible. 1 2(e)(ii) M1 (100, 0.360) and (315, 0.180) 2 M2 half-life correctly calculated from points listed for M1 (x1–x2) when y = 2y 2 1 2(e)(iii) first order 1 AND half-lives are constant (within experimental error) © Cambridge University Press & Assessment 2024 Page 7 of 7

1(a) NO is a toxic gas 1 2 1(b) To be able to determine the accurate mass of brass that has been transferred (by difference) 1 1(c) (10 cm3) volumetric pipette 1 1(d) 0.0600 mol dm–3 aqueous sodium thiosulfate 1 1(e) M1 Volume of 0.200 mol dm–3 Na S O (aq) = 30.00 cm3 3 2 2 3 M2 Using burette transfer 30.00 cm3 of Na S O ((aq)) and add to a volumetric flask. 2 2 3 M3 Top the (100 cm3 volumetric) flask up to 100 cm3 mark with distilled water 1(f) 1.00 g 1 1(g)(i) 1 rough 1 2 3 20.80 20.30 20.55 20.40 1(g)(ii) (20.30 + 20.40) ÷ 2 = 20.35 (cm3) 1 1(g)(iii) 2  0.05 1 Working must be shown  100 = 0.490 20.40 1(h)(i) = (0.0600  17.35/1000) = 1.04  10–3 / 0.00104 1 1(h)(ii) = 5.21  10–4 / 0.000521 1 1(h)(iii) = 1.04  10–3 / 0.00104 1 © Cambridge University Press & Assessment 2025 Page 5 of 7 1(h)(iv) 1.041  10–3  10  63.5 = 0.661 1 1(h)(v) 0.661/1.05  100 = 63.0 1 Question Answer Marks

2(a) 2 M1 Correctly placed vertical condenser including jacket. M2 (Cold) water in at bottom and water out at the top of the condenser 2(a)(ii) anti-bumping granules 1 2(b) M1 thymolphthalein 2 M2 As KOH is used up the pH range of colour change is within the range of change in the pH of mixture 2(c) There is a spot in the reaction mixture chromatogram with same R value as the spot on the ester chromatogram. 1 f 2(d) fractional distillation 1 2(e) The spectrum does not contain an absorption at 1710–1750 cm–1 1 © Cambridge University Press & Assessment 2025 Page 6 of 7 2(f) 3 shift splitting peak structure area 1.2 doublet 6 –CH 3 2.2 singlet 1 –OH 4.0 multiplet 1 >CH–O M1 Row 2 correct M2 Row 3 correct M3 propan-2-ol 2(g) H 2 H O H C H H C C O C H H H C H H M1 correct displayed formula of an ester link M2 correct displayed formula of ester X 2(h) The pH remains below 3.0 1 © Cambridge University Press & Assessment 2025 Page 7 of 7

1(a) M1 bromobenzene is a skin irritant 2 M2 toxic gas(es) (are produced) 1(b)(i) warm in an oven 1 1(b)(ii) fractional distillation 1 1(c)(i) arrow pointing inwards at lower entry to condenser with label ‘water in’ 1 1(c)(ii) to prevent water getting into the apparatus 1 1(c)(iii) to avoid pressure build up in the apparatus 1 1(d) M1 order of weighing 1 1 weighing boat + Mg is weighed 2 weighing boat is weighed after Mg is transferred M2 table + units 1 / g 1 Mass of boat + Mg (before transfer) 2 Mass of boat (+ residue of Mg) (after transfer) Mass of Mg powder (transferred) 1(e) 5.23 cm3 1 1(f) to prevent the reaction becoming too violent 1 1(g) hydrochloric acid is in excess 1 1(h) beaker B 1 AND ethoxyethane is less dense than water © Cambridge University Press & Assessment 2025 Page 7 of 10 1(i)(i) M1 (n(bromobenzene) = 0.0500) 2 n(ethanal) = 3.00 cm3 × 0.788 g cm–3 / 44.0 = 0.0537 mol (Ratio is 1:1) (bromobenzene is the limiting reagent) M2 0.05 mol 1-phenylethanol has a mass of 0.05 mol × 122.0 g mol–1 = 6.10 g Percentage yield = 2.17 g / 6.10 g × 100% = 35.6 % 1(i)(ii) the product contains unreacted ethanal 1 Question Answer Marks

2(a) M1 the solution becomes more dilute 2 M2 the temperature is reduced 2(b) appearance of a (permanent) pink colour 1 © Cambridge University Press & Assessment 2025 Page 8 of 10 2(c)(i) 2 Time / mins Titre, V / cm3 (V – V) / cm3 log[(V – V) / cm3] t f t f t 0 12.00 33.70 1.528 5 16.40 29.30 1.467 10 22.15 23.55 1.372 15 23.45 22.25 1.347 20 26.30 19.40 1.288 25 28.70 17.00 1.230 180 45.70 M1 column 3 correct M2 column 4 correct to four significant figures as log(column 3) 2(c)(ii) M1 six points correctly plotted 2 M2 straight line of best fit drawn 2(c)(iii) anomalous point circled 1 AND the actual time of the sample removed in step 4 was higher than the recorded time (10 mins) 2(c)(iv) M1 co-ordinates read and recorded correctly 2 M2 gradient to three significant figures 2(d) M1 gradient (in s–1) = –k / 2.303 OR k = –gradient × 2.303 2 M2 k = –(c)(iv) × 2.303 / 60 © Cambridge University Press & Assessment 2025 Page 9 of 10 2(e) not reliable 1 AND there is an anomalous point 2(f) straight line sketched with more negative gradient with the same intercept 1 © Cambridge University Press & Assessment 2025 Page 10 of 10

1(a)(i) 8.76 (g) 1 1(a)(ii) M1 dissolve the solid / ethanedioic acid (in the beaker) using (a small volume of) (distilled) water 3 M2 transfer / add to a (500 cm3 volumetric) flask AND rinse (with distilled water) M3 top the 500 cm3 volumetric flask up to mark (with distilled water) AND (stopper and) invert the flask 1(b) wear chemically resistant gloves 1 1(c) to remove water from (the surface of) the activated carbon 1 1(d) 4.0 (cm3) 1 1(e) burette 1 1(f) to ensure a uniformly mixed sample 1 © Cambridge University Press & Assessment 2025 Page 7 of 10 1(g)(i) 1 time / mass of non-adsorbed mass of (COOH) 2 mins (COOH) in 5.0 cm3 adsorbed by activated 2 sample / mg carbon in 5.0 cm3 sample / mg 0 2.50 0.00 5 1.90 0.60 15 1.52 0.98 30 1.43 1.07 45 0.99 1.51 60 0.88 1.62 90 0.81 1.69 120 0.80 1.70 150 0.80 1.70 1(g)(ii) M1 all points plotted correctly 2 M2 smooth curved line of best fit passing close to all points except marked anomaly 1(g)(iii) time (of sample removal) 1 1(g)(iv) temperature 1 1(g)(v) anomalous point circled (at 30 mins) 1 AND the actual time (of removing sample) was less than recorded time (30 minutes) © Cambridge University Press & Assessment 2025 Page 8 of 10 1(h)(i) M1 co-ordinates correctly recorded from line given in Fig 1.2 3 M2 gradient calculated to at least two significant figures M3 units = g mg–1 (h)(ii) q = 1 / gradient in (h)(i) 1 0 1(h)(i) percentage error of experimental result compared to data book value 1 (86.0−78.1) =  100% = 9.2% 86.0 AND 9.2% > 6.5% AND other factors contributed towards error Question Answer Marks

2(a) M1 change in temperature of water / C = 57.3 2 M2 mass of butane burned / g = 2.10 2(b) 320 g  4.18 J g–1 K–1  57.3 K = 76 600 (J) 1 2(c) M1 number of moles of butane burned = 0.0362 mol 2 M2 ∆H = –2120 (kJ mol–1) c 2(d) stir the water before taking reading 1 2(e) 2.5 / 320  100% = 0.78% 1 2(f) use a lid 1 2(g)(i) percentage error (of temperature change or mass change of butane) increases 1 © Cambridge University Press & Assessment 2025 Page 9 of 10 2(g)(ii) less heat loss 1 © Cambridge University Press & Assessment 2025 Page 10 of 10

1(a) M1 bromobenzene is a skin irritant 2 M2 toxic gas(es) (are produced) 1(b)(i) warm in an oven 1 1(b)(ii) fractional distillation 1 1(c)(i) arrow pointing inwards at lower entry to condenser with label ‘water in’ 1 1(c)(ii) to prevent water getting into the apparatus 1 1(c)(iii) to avoid pressure build up in the apparatus 1 1(d) M1 order of weighing 1 1 weighing boat + Mg is weighed 2 weighing boat is weighed after Mg is transferred M2 table + units 1 / g 1 Mass of boat + Mg (before transfer) 2 Mass of boat (+ residue of Mg) (after transfer) Mass of Mg powder (transferred) 1(e) 5.23 cm3 1 1(f) to prevent the reaction becoming too violent 1 1(g) hydrochloric acid is in excess 1 1(h) beaker B 1 AND ethoxyethane is less dense than water © Cambridge University Press & Assessment 2025 Page 7 of 10 1(i)(i) M1 (n(bromobenzene) = 0.0500) 2 n(ethanal) = 3.00 cm3 × 0.788 g cm–3 / 44.0 = 0.0537 mol (Ratio is 1:1) (bromobenzene is the limiting reagent) M2 0.05 mol 1-phenylethanol has a mass of 0.05 mol × 122.0 g mol–1 = 6.10 g Percentage yield = 2.17 g / 6.10 g × 100% = 35.6 % 1(i)(ii) the product contains unreacted ethanal 1 Question Answer Marks

2(a) M1 the solution becomes more dilute 2 M2 the temperature is reduced 2(b) appearance of a (permanent) pink colour 1 © Cambridge University Press & Assessment 2025 Page 8 of 10 2(c)(i) 2 Time / mins Titre, V / cm3 (V – V) / cm3 log[(V – V) / cm3] t f t f t 0 12.00 33.70 1.528 5 16.40 29.30 1.467 10 22.15 23.55 1.372 15 23.45 22.25 1.347 20 26.30 19.40 1.288 25 28.70 17.00 1.230 180 45.70 M1 column 3 correct M2 column 4 correct to four significant figures as log(column 3) 2(c)(ii) M1 six points correctly plotted 2 M2 straight line of best fit drawn 2(c)(iii) anomalous point circled 1 AND the actual time of the sample removed in step 4 was higher than the recorded time (10 mins) 2(c)(iv) M1 co-ordinates read and recorded correctly 2 M2 gradient to three significant figures 2(d) M1 gradient (in s–1) = –k / 2.303 OR k = –gradient × 2.303 2 M2 k = –(c)(iv) × 2.303 / 60 © Cambridge University Press & Assessment 2025 Page 9 of 10 2(e) not reliable 1 AND there is an anomalous point 2(f) straight line sketched with more negative gradient with the same intercept 1 © Cambridge University Press & Assessment 2025 Page 10 of 10

1(a)(i) 0.9976 (g cm–3) 1 1(a)(ii) M1 mass of water = 161.175 – 31.022 g = 130.153 g 2 M2 volume = mass of water / density in (a)(i) = 130.153 / 0.9976 = 130.466 (cm3) 1(b)(i) to ensure the vapour (Y) (in the conical flask) has reached the temperature (of the boiling water / 100 °C) 1 1(b)(ii) mass of vapour (occupying flask)(at step 7) is used in calculation 1 1(b)(iii) (perform the experiment in a) fume hood 1 1(c)(i) (0.00052) 100 1 = 3.21  10–3 (%) 31.123 1(c)(ii) M1 correct value and units used for each quantity 2 • 99000 Pa • 1.2956  10–4 m3 (129.56  10–6) • 373 K (273 +100) M2 rearranges equation to give n=pV / RT AND correct evaluation 99000 129.56 10−6 n= 8.31 373 = 4.138055  10–3 (mol) 1(c)(iii) M = 0.306 / (c)(ii) = 73.94778 1 r 1(d) (calculated Mr would be) greater (than true value) 1 AND mass of vapour measured is greater (all other measurements are the same) 1(e) temperature (of water bath) not high enough (to boil methylbenzene) 1 © Cambridge University Press & Assessment 2025 Page 7 of 9

2(a) 24.15 (g) 1 2(b) M1 add a (small) volume of (distilled) water (to the small beaker) 3 AND dissolve the solid / Cu(NO ) ⦁3H O(s) 3 2 2 M2 transfer the solution to a 100 cm3 volumetric flask with washings M3 make up to the (calibration) mark / line (with distilled water) AND invert the (stoppered) flask (to mix) 2(c) to allow ion(s) to move (between half-cells / two beakers) 1 2(d) 1 log [Mn+] electrode potential of Mn+(aq) / M(s) / V –2.00 –2.958 –2.30 –2.967 –3.00 –2.988 –3.30 –3.006 –4.00 –3.017 –5.00 –3.047 2(e) concentration of Mn+ ((aq)) 1 2(f)(i) M1 points plotted correctly 2 M2 straight line of best fit drawn © Cambridge University Press & Assessment 2025 Page 8 of 9 2(f)(ii) point most anomalous to the plotted line of best fit circled 1 AND the actual concentration of the solution was lower than recorded value (5.00  10–4) 2(f)(iii) repeat the procedure for the solution giving an anomalous result 1 2(g)(i) M1 two acceptable coordinates from line of best fit expressed in the form (x,y) 2 M2 gradient correctly calculated from points listed for M1 to three significant figures 2(g)(ii) y = E 3 m = 2.303RT / nF c = E⦵ 2(g)(iii) M1 correct rearrangement AND values 2 2.303 8.31  298 n = gradient 9.65 1 04 M2 correctly calculated value rounded to whole number © Cambridge University Press & Assessment 2025 Page 9 of 9

1(a)(i) 2.12 g 1 1(a)(ii) M1 add a (small) volume of (distilled) water (to the small beaker) 3 AND dissolve the solid / AgNO (s) 3 M2 Transfer the solution and washings (using a funnel) AND into a 250 cm3 volumetric flask. M3 Make up to the (calibration) mark / line with distilled water. AND then invert the (stoppered) flask (several times) 1(b)(i) (20(.0) cm3) pipette. 1 1(b)(ii) barium (ions) could react with chromate (ions). 1 1(b)(iii) Potassium chromate(VI) / K CrO (aq) is an irritant / corrosive 1 2 4 1(c)(i) They are (the only ones that are) concordant. 1 1(c)(ii) 20.05 1 100 = 0.48(54%) 20.60 Correct working must be shown. 1(d)(i) 20.65  0.05 / 1000 = 0.00103(25) 1 1(d)(ii) = ((d)(i) / 2) *(250 / 20) 1 = (d)(i)  6.25 © Cambridge University Press & Assessment 2025 Page 7 of 10 1(d)(iii) M1 M = 1.58 / (d)(ii) 2 r M2 x= (M1 – 208.3) / 18 AND x must be an integer. Some working must be shown. 1(e) Heat to drive off water of crystallisation. 3 M1 Apparatus 1 Bunsen burner. 2 Crucible (supported by pipeclay triangle) M2 Measurements 1 Measure mass of crucible (+ lid) (empty). 2 Measure mass crucible (+ lid) + solid before heating 3 Measure mass of crucible (+ lid) + residue (after heating.) M3 Key step in method • Description of heat to constant mass. OR Produce a suitable precipitate using a viable reaction. M1 Apparatus and method • Chooses suitable reagent. • Filter the precipitate. • Wash and (allow to) dry M2 Measurements • Measure mass of hydrated barium chloride used. • Measure mass of precipitate. M3 Key step in method • Description of dry to constant mass. © Cambridge University Press & Assessment 2025 Page 8 of 10

2(a) To ensure no air / other gas remains in the syringe 1 2(b)(i) 2 1 0.707 0.500 0.222 0.158 0.109 Mr Rate of effusion /cm3s-1 4.63 3.27 1.45 1.26 0.71 2(b)(ii) Time (taken). 1 2(b)(iii) size of hole 1 2(c) M1 all 5 points plotted correctly. 2 M2 Straight line of best fit drawn 2(d) Point most anomalous to the plotted line of best fit circled. 1 AND If point above LOBF (Measured rate of effusion is higher than the true rate predicted by LOBF.) for this point … measured / recorded (effusion) time < true / actual time OR If point below LOBF (Measured rate of effusion is lower than the true rate predicted by LOBF.) for this point … measured / recorded (effusion) time > true / actual time 2(e) Yes AND The graph / LOBF… 1 is a straight-line AND it goes through the origin. 2(f) The results are not reliable as there is an anomalous result. 1 © Cambridge University Press & Assessment 2025 Page 9 of 10 2(g)(i) M1 Effusion rate = 50/31.6 = (1.58) 1 1 Correct value for read from x-axis Mr M2 Value correctly converted to M 1 . 2(g)(ii) If calculated M > 16 1 (The average) M(of the other components) is greater than 16 / calculated value for g(i). 2(h) (Rate of effusion) increases 1 AND (At higher temperature) gas particles move more quickly. © Cambridge University Press & Assessment 2025 Page 10 of 10

1(a) 0.486 g 1 1(b) M1 Dissolve the solid / KSCN(s) in (the beaker) (using a small volume of) (distilled) water 3 M2 Transfer/add to a (250 cm3 volumetric) flask and Rinse (with distilled water) M3 Top the 250 cm3 volumetric flask up to mark (with distilled water) and Invert the (stoppered) flask Allow ‘250 volumetric flask’ (i.e. units need not be seen) 1(c)(i) to avoid oxidation (of contents of flask) 1 1(c)(ii) to ensure that equilibrium has been reached 1 1(c)(iii) Silver / Ag 1 1(d)(i) (yes) 1 and two titres (2 and 3) are within 0.10 cm³ (of each other) 1(d)(ii) Working must be shown 1 2  0.05 =  100 = 0.457% 21.90 1(d)(iii) percentage error (in larger titre) is lower 1 1(e)(i) 0.0437 mol dm–3 1 1(e)(ii) 0.00630 mol dm–3 1 © Cambridge University Press & Assessment 2025 Page 8 of 11 1(e)(iii) M1 K = 0.00630 / (0.04370)2 = 3.30 1 c M2 units = dm3 mol–1 1 1(f)(i) No 1 and As temperature increases, K c decreases 1(f)(ii) (data points that obey a line of best fit are reliable because) there are no anomalous points. 1 1(f)(iii) exothermic 1 and As temperature increases: K decreases c or equilibrium shifts to left Question Answer Marks

2(a)(i) (25.0 cm3) volumetric pipette 1 2(a)(ii) (wear) chemically resistant gloves 1 © Cambridge University Press & Assessment 2025 Page 9 of 11 2(b)(i) 2 Total volume Corrected in beaker / conductivity cm3 / S cm–1 25.00 37000 30.00 27600 35.00 16800 40.00 3680 45.00 9000 50.00 24000 55.00 39600 60.00 50400 65.00 63700 M1 Total volume in beaker values M2 Corrected conductivity values 2(b)(ii) volume of 0.100 mol dm–3 Ba(OH) (aq) added to beaker 1 2 2(c) M1: all points 1–4 and 5–9 plotted correctly 2 M2: two straight lines of best fit line drawn going through most points. lines must intersect. Place M2 tick in ‘V’ of graph Place M1 tick or cross on left hand side of grid Place cross (or highlight) against mis-plot © Cambridge University Press & Assessment 2025 Page 10 of 11 2(d)(i) intersection point volume (read from within grid) 1 2(d)(ii) nSO 2– =0.100  ans (d)(i) / 1000 = mol 1 4 [SO 2–(aq)] = [0.100  (d)(i) / 1000] / 0.025 4 2(e)(i) diagram showing labelled filter paper in a labelled (filter) funnel 1 2(e)(ii) wash the residue with distilled water 1 2(e)(iii) heat to constant mass 1 2(e)(iv) higher value 1 and (water would cause) (measured) mass / amount (of residue) would be greater © Cambridge University Press & Assessment 2025 Page 11 of 11

1(a)(i) 2.12 g 1 1(a)(ii) M1 add a (small) volume of (distilled) water (to the small beaker) 3 AND dissolve the solid / AgNO (s) 3 M2 Transfer the solution and washings (using a funnel) AND into a 250 cm3 volumetric flask. M3 Make up to the (calibration) mark / line with distilled water. AND then invert the (stoppered) flask (several times) 1(b)(i) (20(.0) cm3) pipette. 1 1(b)(ii) barium (ions) could react with chromate (ions). 1 1(b)(iii) Potassium chromate(VI) / K CrO (aq) is an irritant / corrosive 1 2 4 1(c)(i) They are (the only ones that are) concordant. 1 1(c)(ii) 20.05 1 100 = 0.48(54%) 20.60 Correct working must be shown. 1(d)(i) 20.65  0.05 / 1000 = 0.00103(25) 1 1(d)(ii) = ((d)(i) / 2) *(250 / 20) 1 = (d)(i)  6.25 © Cambridge University Press & Assessment 2025 Page 7 of 10 1(d)(iii) M1 M = 1.58 / (d)(ii) 2 r M2 x= (M1 – 208.3) / 18 AND x must be an integer. Some working must be shown. 1(e) Heat to drive off water of crystallisation. 3 M1 Apparatus 1 Bunsen burner. 2 Crucible (supported by pipeclay triangle) M2 Measurements 1 Measure mass of crucible (+ lid) (empty). 2 Measure mass crucible (+ lid) + solid before heating 3 Measure mass of crucible (+ lid) + residue (after heating.) M3 Key step in method • Description of heat to constant mass. OR Produce a suitable precipitate using a viable reaction. M1 Apparatus and method • Chooses suitable reagent. • Filter the precipitate. • Wash and (allow to) dry M2 Measurements • Measure mass of hydrated barium chloride used. • Measure mass of precipitate. M3 Key step in method • Description of dry to constant mass. © Cambridge University Press & Assessment 2025 Page 8 of 10

2(a) To ensure no air / other gas remains in the syringe 1 2(b)(i) 2 1 0.707 0.500 0.222 0.158 0.109 Mr Rate of effusion /cm3s-1 4.63 3.27 1.45 1.26 0.71 2(b)(ii) Time (taken). 1 2(b)(iii) size of hole 1 2(c) M1 all 5 points plotted correctly. 2 M2 Straight line of best fit drawn 2(d) Point most anomalous to the plotted line of best fit circled. 1 AND If point above LOBF (Measured rate of effusion is higher than the true rate predicted by LOBF.) for this point … measured / recorded (effusion) time < true / actual time OR If point below LOBF (Measured rate of effusion is lower than the true rate predicted by LOBF.) for this point … measured / recorded (effusion) time > true / actual time 2(e) Yes AND The graph / LOBF… 1 is a straight-line AND it goes through the origin. 2(f) The results are not reliable as there is an anomalous result. 1 © Cambridge University Press & Assessment 2025 Page 9 of 10 2(g)(i) M1 Effusion rate = 50/31.6 = (1.58) 1 1 Correct value for read from x-axis Mr M2 Value correctly converted to M 1 . 2(g)(ii) If calculated M > 16 1 (The average) M(of the other components) is greater than 16 / calculated value for g(i). 2(h) (Rate of effusion) increases 1 AND (At higher temperature) gas particles move more quickly. © Cambridge University Press & Assessment 2025 Page 10 of 10

1(a) 38.87 g 1 1(b) M1 Dissolve the solid / MnSO .H O / manganese sulfate (in the beaker) using (a small volume of) distilled water 3 4 2 M2 transfer / add to a (100 cm3 volumetric) flask AND rinse (with distilled water) M3 top up the 100 cm3 volumetric flask to mark (with distilled water) AND Invert the (stoppered) flask) 1(c)(i) (wear) chemically resistant gloves. 1 1(c)(ii) dissolving NaOH(s) is (very) exothermic 1 1(d)(i) Oxygen in trapped air could dissolve into the water sample 1 1(d)(ii) (25.0 cm3) volumetric pipette 1 1(d)(iii) To observe the end-point more clearly 1 1(e)(i) M1 1 rough 1 2 3 12.70 13.05 13.15 M2 13.10 cm3 1 1(e)(ii) titrations 2 and 3 are within 0.10 cm3 of each other 1 © Cambridge University Press & Assessment 2025 Page 7 of 11 1(e)(iii) working must be shown 1 2  0.05  100 = 0.760 13.15 1(f)(i) (e)(i) / (2  106) = 6.55  10–6 (mol) 1 1(f)(ii) (f)(i)  10 = 6.55  10–5 (mol) 1 1(f)(iii) (f)(ii)  1.28  105 = 8.38 (mg dm–3) 1 Question Answer Marks

2(a)(i) to increase the rate of drying / removal of (distilled) water 1 2(a)(ii) iodine is not (very) soluble (in water) 1 2(a)(iii) mass change is (too / very) small 1 2(a)(iv) repeat without any iodine 1 2(b) 1 time / s mass of tin reacted / g 0 0.000 100 0.069 200 0.120 300 0.218 400 0.291 500 0.359 © Cambridge University Press & Assessment 2025 Page 8 of 11 2(c)(i) M1 points plotted correctly 1 centre of all crosses should be on line for  value. y value should be on the line for point 1, 3 point 2, 6 – just below line / on line 4 – midway between two lines 5 – just above line / on line M2 straight line of best fit drawn 1 2(c)(ii) most anomalous point circled 1 (expected to be at time 200 s, point 3, below line of best fit) AND the balance/mass reading was taken before 200 s / too early 2(d) M1 two acceptable coordinates from line of best fit expressed in the form (x,y). 2 M2 gradient correctly calculated from points listed for M1. answer correctly rounded to 3 significant figures. © Cambridge University Press & Assessment 2025 Page 9 of 11 2(e)(i) 1 volume of volume of 0.400 mol dm–3 methylbenzene I solution used / cm3 2 used / cm3 100.0 0.0 75.0 25.0 50.0 50.0 25.0 75.0 2(e)(ii) [I ] 1 2 2(e)(iii) M1 no 1 AND the rate of reaction is proportional to the concentration of iodine / a conclusion based on calculations done for M2 M2 explained using actual values from columns 3 and 4 in Table 2.2 1 © Cambridge University Press & Assessment 2025 Page 10 of 11

1(a) 1.200 1 1(b)(i) (2  0.0005 / 7.235)  100 = 0.0138 1 Full working must be shown 1(b)(ii) Increase the mass of X used 1 1(c) M1 Dissolve the solid / X (in the beaker) (using a small volume of) (distilled) water 3 M2 Transfer / add to a (250 cm3 volumetric) flask AND Rinse (with distilled water) M3 Top the 250 cm3 volumetric flask up to mark (with distilled water) AND Invert the (stoppered) flask (several times) 1(d)(i) (wear) chemically resistant gloves 1 1(d)(ii) 25 cm3 volumetric pipette 1 1(d)(iii) NaB(C H ) is added in excess. 1 6 5 4 1(d)(iv) to increase the mass of precipitate / KB(C H ) 1 6 5 4 1(d)(v) to dry the crucible 1 1(d)(vi) 0.01(00) 1 1(d)(vii) 0.746 1 1(e)(i) 0.015(0) 1 1(e)(ii) 0.293 OR 0.2925 1 1(e)(iii) 0.1615 OR 0.162 1 © Cambridge University Press & Assessment 2026 Page 7 of 9 1(f) 1 effect on calculated mass of KCl in 1(d)(vii) Higher effect on calculated mass of NaCl in 1(e)(ii) Lower 1(g) thermal decomposition of the residue / KB(C H ) 1 6 5 4 Question Answer Marks

2(a)(i) 1 Vol of KCl Vol of distilled water added 0.00 50.00 0.50 49.50 1.00 49.00 1.50 48.50 2.00 48.00 2.50 47.50 3.00 47.00 3.50 46.50 4.00 46.00 4.50 45.50 5.00 45.00 2(a)(ii) (50 cm3) burette 1 © Cambridge University Press & Assessment 2026 Page 8 of 9 2(a)(iii) relative light intensity 1 2(a)(iv) M1 all 10 points plotted correctly. 2 M2 both lines of best fit drawn correctly. 2(a)(v) The line of best fit is straight 1 AND passes through (0,0) 2(a)(vi) Point at 6.00  10–3 circled 1 AND too much distilled water was added (to the prepared solution). OR too little KCl (aq) was added (to the prepared solution). 2(b)(i) Correct value of [K+] in diluted sample from graph 1 2(b)(ii) Within the healthy range 1 AND stated undiluted blood plasma has a concentration of 2(b)(i)  100 g dm–3 2(b)(iii) Other (cat)ions (in blood plasma) will emit (other) colours 1 2(c) All concentrations above 8.00  10–3 g dm–3 show the same relative light intensity. 1 OR The calibration graph is flat above [K+] = 8.00 g dm–3 2(d) Not reliable 1 AND there is an anomalous point © Cambridge University Press & Assessment 2026 Page 9 of 9

1(a) pipeclay triangle 1 A clay triangle / clay pipe triangle / triangle clay pipe I tripod, gauze, triangular holder 1(b) to prevent spitting 1 A to prevent cracking / damaging / breaking crucible A to prevent losing solid / (mixture) X / solid jumping out (of crucible) A to prevent splitting A CaCl or Ca(NO ) for solid 2 3 2 R burning 1(c) NO is a hazardous gas 1 A NO gas is toxic / poisonous / acidic / corrosive 2 2 A NO is an irritant to eyes / by inhaling 2 A NO (g) for NO gas 2 2 I flammable, harmful R answers about O 2 1(d)(i) M1 mass lost on heating is 17.81 – 16.53 g = 1.28 g 2 award 2 marks for 0.0237 relative molecular mass of (4NO + O ) = 216.0 award 1 marks for 0.0278, 0.0618, 0.135 and 0.0156 2 2 1.28 g is 1.28 / 216 mol = 0.005926 mol of (4NO + O ) 2 2 1.28 g is NO and O in the ratio of 4:1 2 2 relative mass of (4NO + O ) = 4  14.0 + 10  16.0 = 2 2 216.0 g mol–1 1.28 g is 1.28 / 216 mol = 0.005926 mol of (4NO + O ) 2 2 NO is 4 this. 2 A 2 or more SF M2 number of moles NO = 4  0.005926 = 0.0237 mol ecf from incorrect M1: 2 A a number of moles  4 [A if assume all gas released to be NO = 0.0278 mol 2 A if 5.07 g is assumed to be all Ca(NO ) then 3 2 5.07 / 164.1 = 0.0309 mol Ca(NO ) so 2  0.0309 = 3 2 0.0618 mol A if 3.79 g is assumed to be CaO so 3.79 / 56.1 = 0.06756 mol CaO then 2  0.06756 = 0.135 mol A if 1.28 g is assumed to be Ca(NO ) then 1.28 / 164.1 3 2 = 0.00780 mol Ca(NO ) so 2  0.0078 = 0.0156 mol] 3 2 © Cambridge University Press & Assessment 2026 Page 7 of 13 Trace ID: PC-54A496C6B0 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/5a1 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/51 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(d)(ii) Correct working must be shown. 1 A the following values are amongst acceptable values for the answer following a correct expression 0.06, percentage error = (2  0.005 / 17.81)  100% = 0.0561 0.056, 0.05 etc. I ignore missing  100 if correct answer is given (2  0.005) may be seen as (0.01 / 2  2) 1(d)(iii) increase the mass of mixture X used 1 A any wording that implies increasing the mass of X e.g. weigh a larger sample / reactant / contents A use a bigger amount of X / Use a larger quantity of X / use more X etc. A use a larger mass of ‘crucible + X’ A ‘use a larger mass’ or more than 5.07 g I ‘use a large mass’ alone I repeat and take mean I changes to heating e.g. heat for longer R more accurate balance or any other change to apparatus e.g. increase mass of crucible alone R incorrect use of weight for mass R heat to constant mass 1(e) M1 mol of Ca(NO ) in original sample = 0.5  0.0223 mol = 2 award 2 marks for 36.7 3 2 0.01115 mol A more SF e.g. 1.829715 g 36.741265% A 36.7 rounded to 37 for M2 I rounding errors after 3SF. M2 mass Ca(NO ) in original sample = 0.01115 mol  If M1 is rounded to 0.0112 mol and then used in M2 3 2 164.1 g mol–1 = 1.829715 g award M1 only % by mass Ca(NO ) = 1.829715 / 4.98  100% = 36.7% ecf for M2 from incorrect M1 and allow final answer to 3 2 be rounded to 2SF © Cambridge University Press & Assessment 2026 Page 8 of 13 Trace ID: PC-54A496C6B0 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/5a1 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/51 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(f)(i) heat to constant mass 1 A description of the process of heating to constant mass e.g. reheat and reweigh until mass remains constant A repeat steps 3 and 4 to constant mass response must include (re)heat and constant mass 1(f)(ii) The percentage by mass will be smaller. 1 A NO or O or both for gas 2 2 AND A amount / mol for mass mass of gas lost is smaller (than the maximum possible) OR I not all NO released 2 mass of solid remaining after heating is higher (than actual mass) I calculated mass of Ca(NO ) (that decomposes) is 3 2 lower than actual value 1(g) M1 attempted use of ice / cold water for condensing the gas 2 M1 A coolant/cool water for ice without loss of the NO as gas 2 If a condenser is seen, max 1 mark • must be angled downwards towards unsealed M2 in an unsealed collection vessel surrounded by iced / cold collection vessel water • must show water in and out of jacket • ignore position of water in and out • condensed NO must be delivered into a vessel 2 surrounded by ice/cold water. If a condenser is delivering into a u-tube and ice, then 2 marks can be awarded. © Cambridge University Press & Assessment 2026 Page 9 of 13 Trace ID: PC-54A496C6B0 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/5a1 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/51 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/

2(a) only (direct) light from the LED should be allowed to reach the 1 A to prevent outside light entering (the colorimeter) photocell A to prevent outside light reaching the photocell for outside light A external light / background light /surrounding light for photocell A detector A no (indirect) light via reflections A the only source of light is from the LED I other light for outside light I light absorbed unless it is absorbed by the photocell 2(b)(i) 1 Must be 3 DP concentration of resistance of absorbance, A I –(aq) / mol dm–3 photocell, R / k 3 s 3.60  10-6 34.28 0.839 2.94  10-6 23.42 0.684 2.20  10-6 16.01 0.519 1.52  10-6 9.68 0.300 7.90  10-7 7.50 0.189 2(b)(ii) distilled water (with few drops of starch solution) 1 A (acidified) I–(aq)/solution (with few drops of starch solution) A acidified I– ions (with few drops of starch solution) A I – solution/(aq) with no starch 3 2(b)(iii) concentration of I – 1 3 © Cambridge University Press & Assessment 2026 Page 10 of 13 Trace ID: PC-54A496C6B0 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/5a1 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/51 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(b)(iv) M1 all 5 points plotted correctly 2 Place plotting tick on grid above line of best fit. Place line tick in left-hand margin Place a cross beside an incorrect point M2 straight line of best fit through origin passing through or close ecf from 2(b)(i) to all points except anomaly (point 2) R if point 2 is on a vertical gridline R if point 4 is on a horizontal gridline R line of best fit that does not extend from the origin to cover all plotted points. R if line of best fit is one square or more from origin on either axis A line of best fit between the first and last (correctly plotted) points is acceptable as long as it goes close enough to the origin. All points except anomaly should be on the line of best fit. Point marked as anomalous (ringed) should not be used in determining the line of best fit. A ecf acceptable line of best fit drawn for incorrectly plotted points. R line of best fit if the points (except anomaly) not approximately evenly distributed on both sides of line I extra points added which are used in later calculations I remnants of lines that the candidate has tried to erase R curved line R double or “sketchy” lines. © Cambridge University Press & Assessment 2026 Page 11 of 13 Trace ID: PC-54A496C6B0 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/5a1 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/51 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(b)(v) most anomalous point circled 1 Expected answer is point 2 at (1.52  10–6, 0.300 below the line of best fit) AND A light intensity (in colorimeter) increased any one reason from: • not enough starch added (in step 2) A ora for ecf point above line of best fit • less than 10.0 cm3 solution transferred (from boiling tube to measuring cylinder in step 4) A light got into the colorimeter/black box not shut (no • solution (from step 2) was left for less than 10 minutes (in ora for point above line of best fit) step 3) I reading of absorbance was too low I comments about temperature/heat I starch not mixed properly I systematic error I evaporation I reference to rates 2(c)(i) to allow all the I – ions form a complex (with the starch) 1 A for complete reaction (of the I – ions and starch) 3 3 A enough time for the complex to form completely I to reach equilibrium I reference to rate of reaction I all the starch reacts 2(c)(ii) 10 cm3 volumetric pipette 1 A graduated pipette as long as volume is not < 10 cm3 A 10 cm3 pipette A volumetric pipette I ‘pipette’ alone R burette 2(c)(iii) M1 absorbance = 0.640 2 A 0.64 with working shown Concentration should be read from the graph to nearest ½ square. M2 concentration read from the graph to nearest ½ square and I any figures after 3SF given to 3 SF I trailing zeros (allow 2.7 for 2.70) A non-standard form 2.75  10–6 mol dm–3 is a common answer © Cambridge University Press & Assessment 2026 Page 12 of 13 Trace ID: PC-54A496C6B0 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/5a1 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/51 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(c)(iv) (15 / 1000)  2(c)(iii) 1 A 2 SF minimum A calculator value from 2(c)(iii) (e.g. 2.725 used for 2.73 given in 2(c)(iii)) I trailing zeros A non-standard form 2(c)(v) 2(c)(iv)  (1000 / 7500) 1 If using the given value, then: 3.23  10–8  1000 / 7500 = 4.31  10–9 mol dm–3 A calculator value from 2(c)(iv) A 2 SF minimum A non-standard form 2(c)(vi) increases 1 AND (the value of) the concentration of I – increases (at same 3 absorbance) 2(c)(vii) 9.87 + 0.14  9.87 = 11.25 AND 13.66 – 0.14  13.66 = 11.75 1 A any set of calculations which gives 11.25 and 11.75 AND the concentration of O is different (because the extremes of the 3 ranges do not overlap) 2(c)(viii) R increases 1 A light travels through a deeper solution s AND A light interacts with more I – particles 3 the light has a longer path length (through the solution) A absorbance increases with depth (of solution) I light interacts with more I – solution(aq) 3 I more light is absorbed alone I measuring cylinder is deeper 2(c)(ix) concentration of I – will be higher giving a lower percentage error 1 A amount / mol of I – for concentration of I – 3 3 3 I uncertainty for percentage error A uncertainty percentage error for percentage error alone © Cambridge University Press & Assessment 2026 Page 13 of 13 Trace ID: PC-54A496C6B0 Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. 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1(a)(i) 7.61 g 1 0.300  100/1000  253.8 A 7.614 R 7.62 or 127 or 254 used in working A 7.6 but only if there is no evidence of 7.62 / 127 / 254 © Cambridge University Press & Assessment 2026 Page 7 of 22 Trace ID: PC-3F04F08B6B 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/5a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/52 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(a)(ii) M1 dissolve the solid / I (s) (in the beaker) (using a small 3 M1 is the dissolving mark 2 volume of) methanol M2 is the transfer with rinsing mark into a flask M3 is volumetric apparatus and inversion mark (we need 100 cm3 AND volumetric flask seen somewhere) M1 and M2 could still be awarded if another type of flask (e.g. conical) is used – but must be a flask not a beaker / measuring cylinder M1 I ‘weigh the solid’ I mass / mol I if seen 2 I ‘place in a beaker’ (assume they are repeating the question) but if they transfer the solid to a second container, evidence of rinsing is needed to allow M1 M1 R if it is assumed I is aqueous/in methanol 2 M1 R if suggestion is to add more than 50 cm3 of methanol or to fill the beaker to dissolve solid in the beaker. Any volume quoted must be 50 cm3 or less. A prepare / make a solution for dissolve. If dissolve not seen here, A ‘transfer the solution’ in M2 to be equivalent to ‘dissolve’ in M1 ie they must have dissolved in M1 if they are transferring a solution in M2. M2 transfer/add to a (100 cm3 volumetric) flask M2 A graduated flask for volumetric flask AND A extra transfers as long as the exact number of moles of rinse (with methanol) solid end up in the vol flask via rinsing. Assume ‘rinse’ / ‘wash’ is into flask unless stated I lack of rinsing the funnel M2 R if transfer of solution from M1 is via burette/pipette assume ‘rinse the residue’ refers to residual solution in the beaker M3 top the 100 cm3 volumetric flask up to mark (with M3 A make up to 100 cm3 with methanol. I ‘top up’ without methanol) reference to 100 AND A ‘fill the flask to 100 cm3 / mark’ but R ‘fill the flask’ (alone) invert the (stoppered) flask for ‘invert the flask’ A ‘shake’, ‘swirl’ etc I Homogenise (alone) I ‘mix’ (alone) /‘mix the flask’ (we need to know how they mix/homogenise) R stir in the flask © Cambridge University Press & Assessment 2026 Page 8 of 22 Trace ID: PC-3F04F08B6B 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/5a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/52 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(a)(ii) A max 2 marks if solid is added directly into the volumetric flask M1 is not awarded M2 rinsing of beaker is still needed to ensure all the solid is put into the vol flask M3 OK If they fill volumetric flask to the mark / add 100 cm3 of methanol and then add solid A max 1 mark: M1 is not awarded M2 is not awarded (because they cannot rinse into a full flask) M3 still possible for 100 cm3 volumetric flask AND methanol AND invert to gain credit ‘100 cm3 volumetric flask’ needs to be seen in M2 or M3 for M3 to be awarded Methanol needs to be seen at least once in M1, M2 or M3 without methanol 3 marks = 2 marks, 2 marks = 1 and 1 mark = 0 marks. methanol must be seen once to award M1 if not directly used in M1 max 2 marks if (distilled) water is used as the solvent © Cambridge University Press & Assessment 2026 Page 9 of 22 Trace ID: PC-3F04F08B6B 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/5a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/52 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(b)(i) methanol is flammable 1 A inflammable for flammable R non-flammable A other comments implying the flammability of methanol e.g. methanol vapours ignite A solution / I (meth) / substance is flammable A solvent is 2 flammable I I (alone) is flammable 2 A tetramethylammonium iodide / (CH ) NI is flammable A 3 4 reactants are flammable A contents are flammable A polyiodide salt / (CH ) NI is flammable A product(s) are 3 4 2n+1 flammable I ‘(it is) flammable’ alone (not specifying whether it is the contents or the flask which is flammable) I references to explosions I to reduce evaporation of methanol / prevent methanol boiling I (CH ) NI / reactant will (thermally) decompose 3 4 I to avoid spitting I flask shattering / flask breaking 1(b)(ii) to remove any soluble impurities 1 A to remove impurites / to remove reactants / I / I (meth) 2 2 / (CH ) NI 3 4 A to remove solute(s) / A to remove solution(s) A to remove (methanol-)soluble substances (no need to tell us what the substances are) I to remove substances (alone) I to remove filtrate R to remove product / residue / solid impurities R to remove methanol / solvent / water © Cambridge University Press & Assessment 2026 Page 10 of 22 Trace ID: PC-3F04F08B6B 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/5a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/52 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(b)(iii) leave (to dry) 1 A description of leaving until constant mass e.g. keep on weighing until constant mass AND e.g. weigh every 5 minutes until constant mass e.g. dry to constant mass until constant mass e.g. repeat drying and weighing until a constant mass is obtained e.g. wait until constant mass R heating or methods which do not reflect step 6 (where heating does not occur) e.g. heat to constant mass / place in an oven until constant mass / leave in a warm place I use of cobalt chloride paper / desiccator R leave until constant volume R constant weight for constant mass © Cambridge University Press & Assessment 2026 Page 11 of 22 Trace ID: PC-3F04F08B6B 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/5a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/52 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(b)(iv) M1 suitable results table showing rows which include: 2 mark table first • mass of (evaporating) basin the table may be vertical as well as horizontal • mass of (evaporating) basin + crystals A ‘weight’ for ‘mass’ in this question only • mass of crystals ‘mass’ must be seen in table • with column to enter values A dish for basin • units i.e. ‘g’ A any table that has: e.g. mass of dish / weighing boat / any container + crystals mass of (evaporating) basin / g mass of dish / weighing boat / any container (ignore ‘+ residue’) mass of (evaporating) basin + crystals / g mass of crystals / product / (CH ) NI / solid 3 4 2n+1 units i.e. ‘g’ mass of crystals / g A rows 1 and 2 in any order I other rows R tables which do not have a container R tables which do not measure mass of crystals (e.g. tables which only measure mass change due to methanol/water loss e.g. ‘wet crystals to dry crystals) I mass change due to solvent loss as extra row(s) R tables which measure mass of stated substance other than crystal/product e.g. I 2 allow units in value box (as shown) mass Mass of evaporating g basin © Cambridge University Press & Assessment 2026 Page 12 of 22 Trace ID: PC-3F04F08B6B 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/5a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/52 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(b)(iv) M2 description of correct method used in obtaining mass of A as an alternative description of correct method for M2: dry crystals • weigh an evaporating basin + crystals • Weigh an evaporating basin • rinse and dry the evaporating basin and reweigh • (Transfer the dry crystals from the filter paper to the I descriptions of maths involved in determining mass of evaporating basin and) reweigh the evaporating basin + crystals crystals. other methods which involve transfer of crystal from the original basin into another container (might be a basin) will not score M2 e.g. • weigh a weighing boat (or other container) • transfer the crystals from the evaporating basin to the weighing boat / container and reweigh weighing boat/container 1(c)(i) 0.0200 mol dm–3 Na S O (aq) 1 A Na S O (aq) / aqueous sodium thiosulfate / 0.02 mol dm–3 2 2 3 2 2 3 Na S O 2 2 3 A sodium thiosulfate / Na S O alone without aqueous 2 2 3 A rinse with solution to be used in the burette I slips in concentration e.g. 0.2 mol dm–3 I rinsing with distilled water or organic drying solvent e.g. propanone before rinsing with Na S O (aq). 2 2 3 R rinsing with anything else after Na S O (aq). 2 2 3 R incorrect formulae R ‘rinse with water/ Na S O (aq)’ (too vague) 2 2 3 © Cambridge University Press & Assessment 2026 Page 13 of 22 Trace ID: PC-3F04F08B6B 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/5a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/52 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(c)(ii) Working must be shown. = © Cambridge University Press & Assessment 2026 Page 14 of 22 2 1  3 0 . . 3 0 5 5 1 (0.05  2) may be seen separate or as (0.1 / 2  2) I 0.1 as numerator without evidence of 0.05 A Any correct answer that rounds to 0.7 i.e. A  100 = 0.749% 0.7 / 0.74 / 0.749 A 0.75 / 0.750 I missing ‘x 100’ in calculation if correct answer seen I Rounding errors beyond 1st SF R 0.0749 this must mean 0.005 was used in the working R incorrect answers with correct working Titre used must be 13.35 1(c)(iii) 13.30 cm3 1 I 13.3 Trace ID: PC-3F04F08B6B 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/5a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/52 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(c)(iv) M1 mol of Na S O in mean titre 3 A 3 marks for 0.338 if no evidence of incorrect working. I 2 2 3 = 13.30 cm3  0.02 / 1000 minor transcription errors = 2.66  10-4 mol A 0.338 up to calculator value (0.337554) I RE after 3rd SF A 2SF as final answer if 3SF or more correct answer seen in working M2 mol of I in 10 cm3 of solution A Otherwise mark by step. 2 = 2.66  10-4 / 2=1.33  10-4 mol M2 subsumes M1 and A ecf for mean titre from 1(c)(iii) mol of I in 100 cm3 of solution A 2 A M2 for ecf of M1 =1.33  10-4 mol  100 / 10 =1.33  10-3 mol A M3 for ecf of M2 M3 mass of I in 100 cm3 of solution A = 1.33  10-3  253.8 2 A Use of 254 =0.338 g A ecf for use of 126.9 / 127 for M I if used in 1(a)(i) r 2 Scaling up by 100 / 10 appears in step 2, but can appear in any step. A mole ratio methods involving concentration  volume of solutions C  V C = [I (aq)] in solution A V = volume solution A 1 1 1 2 1 C  V C = [Na S O (aq)] V = volume Na S O (aq) 2 2 2 2 2 3 2 2 2 3 concentration of I (in soln A)  volume I (soln A) = 1 2 2 concentration of Na S O  volume Na S O 2 2 2 3 2 2 3 concentration of I  10.00 = 1 2 0.0200  volume Na S O 2 2 2 3 This leads to [I (aq)] in solution A = 0.0133 mol dm–3 M1 ✓ 2 Moles of I in 100 cm3 of solution A = 0.0133 100 / 1000 = 2 1.33  10–3 M2 ✓ (M2 subsumes M1) 1.33  10-3  253.8 = 0.338 g M3 ✓ Other methods may be used. © Cambridge University Press & Assessment 2026 Page 15 of 22 Trace ID: PC-3F04F08B6B 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/5a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/52 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(c)(v) Working must be shown. 1 The mass (or substitute value) of I from 1(c)(iv) must be 2 used or a derived number of moles from this value must be mol I = 0.338 / 253.8 = 0.00133 mol I seen (moles may be seen in M2 of 1(c)(iv)) 2 2 mass (CH ) NI = 0.472 – 0.338 = 0.134 g A ecf from 1(c)(iv) for 0.338 (mass of I ) 3 4 2 mol (CH 3 ) 4 NI = 0.134/200.9 = 0.000667 mol A ecf for M r I 2 = 126.9 / 127 if 126.9 / 127 was used in 1(a)(i) ratio = 0.00133 = 1.99… (= 2) Apply the following formulas to help 0.000667 If 253.8 is used as M I r 2 n = 0.7916  a where a = answer to (c)(iv) AND (0.472–a) n = 2 If 126.9 is used as M I r 2 n = 1.583 x a where a = answer to (c)(iv) (0.472–a) A as minimum seen for working: 0.338 / 253.8 and (0.472 – 0.338) / 200.9 or 0.134 / 200.9 or 0.00133 mol I and 0.000667 mol of (CH ) NI 2 3 4 or 1.99… A mol of I = 0.00133 or mol of I derived from incorrect 2 2 mass of I in 1(c)(iv) 2 and A mol of (CH ) NI = 0.000667 or mol of (CH ) NI derived 3 4 3 4 from incorrect mass of I in 1(c)(iv) 2 Using given 0.374 g as the mass of I gives n = 3. 2 Other methods may be used. © Cambridge University Press & Assessment 2026 Page 16 of 22 Trace ID: PC-3F04F08B6B Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. 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2(a) M1 labelled gas syringe 2 M1 gas syringe must be attached (directly to) side arm R M1if delivery to gas syringe goes through extra apparatus eg condenser etc A ‘syringe’ / ‘glass syringe’ as label A for displacement of non-aqueous named liquid (instead of water) into an inverted labelled measuring cylinder M2 M2 sealed apparatus using a bung / cork / stopper A for any apparatus that is sealed and is capable of collecting a measured volume of gas e.g. displacement of water using a measuring cylinder e.g. gas syringe coming from hole in bung and side arm sealed A ‘lid’ as label for a clearly drawn bung. A ‘bung’ as label for what looks like a lid R lid as a label if it looks like a lid R if ‘sealed’ apparatus includes addition of solution that would push air into the gas syringe e.g. burette delivering a solution through the bung. I attempts at mixing solutions within sealed apparatus e.g. test-tube dangling on a string I lines across delivery tubes A for loose diagrams - if it looks like a bung at the top of the flask assume it to be sealed A non-tight connection of delivery tubes to side arm A loose piston in the gas syringe R sealed apparatus that would pop apart due to increased pressure © Cambridge University Press & Assessment 2026 Page 17 of 22 Trace ID: PC-3F04F08B6B 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/5a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/52 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(a) If M2 (or M1) is given for a displacement of water apparatus be lenient with position of delivery tube at the bottom of the measuring cylinder. But it should not ‘enter’ the measuring cylinder above the water line or go through the wall of the water trough R M1 and M2 if a syringe being used to deliver reactants 2(b) time 1 I units R ‘time intervals’ 2(c) the volume (of CO ) was measured / recorded too 1 A (recorded) time is greater than actual time 2 early / before 1000s for actual time A true time / real time for recorded time A time read / the time (seen) in the results table A reading was taken / recorded / measured at (880 – 920) s / (120 – 80) s early R timer was started / stopped too early / late I comments on volume error assume ‘the time was recorded’ means ‘the recorded time’ i.e. ‘time was recorded too late’ is correct i.e. ‘time was recorded too early’ is incorrect 2(d) a smooth curve that: 1 I points drawn on curve • starts at the origin A curve to start within first four small squares of y-axis and at 0 on the x-axis • is to the left of the original curve R curves which cross original graph R curves which clearly stray outside y-axis • flattens at 10 cm3 and before 1300 s A curves to stray up to a ¼ of a square above 10 cm3 as a ‘hump AND return to 10 cm3 R curves (with humps) that go too high above 10 cm3 • ends at 1600s R curves where horizontal part stops before 1400s © Cambridge University Press & Assessment 2026 Page 18 of 22 Trace ID: PC-3F04F08B6B 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/5a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/52 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(e)(i) 2 all values must be to 2 DP [Na S O ] rate log log 2 2 8 A ecf for M2 if all –ve signs are missing in both columns / moldm−3 / moldm−3s−1 [Na S O ] (rate) 2 2 8 A ecf for -1.93 in column 4 if –2.43 is seen in column 3 A ecf for both –2.4 AND –2.6 seen in column 4 if –2.(0) AND 1.00 x 10–2 0.02760 –2.00 –1.56 –2.8 is seen in column 3 5.74 x 10–3 0.01160 –2.24 –1.94 3.67 x 10–3 0.00549 –2.44 –2.26 2.88 x 10–3 0.00398 –2.54 –2.40 2.08 x 10–3 0.00250 –2.68 –2.60 1.57 x 10–3 0.00169 –2.80 –2.77 ✓ ✓ M1 column 3 M2 column 4 © Cambridge University Press & Assessment 2026 Page 19 of 22 Trace ID: PC-3F04F08B6B 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/5a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/52 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(e)(ii) M1 all 6 points correctly plotted 2 If a point should be on a line, it must be on a line. If a point should not be on a line, it must not be on a line. If not supposed to be on the line, points must be within half a small square of the correct position and in the correct small square. Blobs/thick crosses should be less than ½ a square across and be correctly centred. M2 line of best fit correctly drawn A ecf for acceptable line of best fit for incorrectly plotted points I remnants of lines that have been rubbed out place tick for M1 on graph place tick for M2 to the left-hand side of graph Indicate any incorrect plots with colour tool once line of best fit must cover all the points line of best fit guidance: • line should meet right-hand side of grid above –1.6 • point at (–2.24, –1.94) should not be significantly above the line. 2(e)(iii) M1 co-ordinates correctly recorded from line of best fit 2 range at least 0.4 units on x-axis table points may be used but must be on line of best fit (beware (–2.00, –1.56)) Co-ordinates should be read to nearest ½ square I any (lack of) trailing zeroes on co-ordinates e.g. A -2.00 as -2 If x, y values are reversed, R ecf of x / y but A M2 for a correct gradient (y / x) M2 gradient calculated and correctly rounded to three I units significant figures © Cambridge University Press & Assessment 2026 Page 20 of 22 Trace ID: PC-3F04F08B6B 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/5a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/52 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(e)(iv) correct values of y, m and x for use in y = mx + c where 1 A ecf of incorrect x and y values from co-ordinates in 2(e)(iii) y and x are coordinates of a point of the line m is gradient calculated in 2(e)(iii) E.g. –1.94 = [2(e)(iii)  –2.24] + log k AND Log k = –1.94 – [2(e)(iii)  –2.24] determination of log k k = 10–1.94 – [2(e)(iii) x –2.24] AND A 1.55 to be used in place of 2(e)(iii) determination of k A gradient from 2(e)(iii) expressed as a fraction or calculator value A correct answer to 2 or more SF I RE after 2nd SF 2(e)(v) Method 1: 1 A other suitable methods [2(e)(iii) – 1.5]  100 OR [1.5 – 2(e)(iii)] = Q% 1.5 1.5 A use of 3/2 instead of 1.5 for true gradient AND (if Q% less than 4.5) AND (measurement) error A 1.55 for their value of 2(e)(iii) OR (if Q% greater than 4.5) AND other factors If their gradient in 2(e)(iii) is 1.50 A 0% to be called ‘an error’ Method 2: A statement ‘there is no error’ 4.5 % of 1.5 = 0.0675 AND 1.5 + 0.0675 = 1.5675 AND / OR 1.5 – 0.0675 = 1.4325 But a qualifying statement about ‘measurement’ error is AND required. 2(e)(iii) between 1.4325 and 1.5 AND / OR between 1.5 AND 1.5675 AND measurement error OR 2(e)(iii) is outside this range AND other factors © Cambridge University Press & Assessment 2026 Page 21 of 22 Trace ID: PC-3F04F08B6B 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/5a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/52 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(e)(vi) it is reliable 1 The answer must match the graph AND no anomalous results/points A ‘(all) the points are on or (very) near to line (of best fit)’ A ‘outliers’ for ‘anomalous points’ A ‘(straight) line passing through / touching all points’ but I ‘straight line passing all points’ OR I ‘line fits the data’ A there is (only) one anomalous point, which must be identified, which can be ignored (and all the other points are on (or very near) line of best fit) it is not reliable I most of the points are on the line of best fit AND Not reliable lines of best fit will come from incorrect data there is an anomalous point plotting causing an anomalous point. Points near but not on the line are not anomalous unless the candidate has indicated this by a circle etc or by identifying the point using co-ordinates. © Cambridge University Press & Assessment 2026 Page 22 of 22 Trace ID: PC-3F04F08B6B 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/5a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/52 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/

1(a) pipeclay triangle 1 A clay triangle / clay pipe triangle / triangle clay pipe I tripod, gauze, triangular holder 1(b) to prevent spitting 1 A to prevent cracking / damaging / breaking crucible A to prevent losing solid / (mixture) X / solid jumping out (of crucible) A to prevent splitting A CaCl or Ca(NO ) for solid 2 3 2 R burning 1(c) NO is a hazardous gas 1 A NO gas is toxic / poisonous / acidic / corrosive 2 2 A NO is an irritant to eyes / by inhaling 2 A NO (g) for NO gas 2 2 I flammable, harmful R answers about O 2 1(d)(i) M1 mass lost on heating is 17.81 – 16.53 g = 1.28 g 2 award 2 marks for 0.0237 relative molecular mass of (4NO + O ) = 216.0 award 1 marks for 0.0278, 0.0618, 0.135 and 0.0156 2 2 1.28 g is 1.28 / 216 mol = 0.005926 mol of (4NO + O ) 2 2 1.28 g is NO and O in the ratio of 4:1 2 2 relative mass of (4NO + O ) = 4  14.0 + 10  16.0 = 2 2 216.0 g mol–1 1.28 g is 1.28 / 216 mol = 0.005926 mol of (4NO + O ) 2 2 NO is 4 this. 2 A 2 or more SF M2 number of moles NO = 4  0.005926 = 0.0237 mol ecf from incorrect M1: 2 A a number of moles  4 [A if assume all gas released to be NO = 0.0278 mol 2 A if 5.07 g is assumed to be all Ca(NO ) then 3 2 5.07 / 164.1 = 0.0309 mol Ca(NO ) so 2  0.0309 = 3 2 0.0618 mol A if 3.79 g is assumed to be CaO so 3.79 / 56.1 = 0.06756 mol CaO then 2  0.06756 = 0.135 mol A if 1.28 g is assumed to be Ca(NO ) then 1.28 / 164.1 3 2 = 0.00780 mol Ca(NO ) so 2  0.0078 = 0.0156 mol] 3 2 © Cambridge University Press & Assessment 2026 Page 7 of 13 Trace ID: PC-B8B10956DE 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/5a3 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/53 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(d)(ii) Correct working must be shown. 1 A the following values are amongst acceptable values for the answer following a correct expression 0.06, percentage error = (2  0.005 / 17.81)  100% = 0.0561 0.056, 0.05 etc. I ignore missing  100 if correct answer is given (2  0.005) may be seen as (0.01 / 2  2) 1(d)(iii) increase the mass of mixture X used 1 A any wording that implies increasing the mass of X e.g. weigh a larger sample / reactant / contents A use a bigger amount of X / Use a larger quantity of X / use more X etc. A use a larger mass of ‘crucible + X’ A ‘use a larger mass’ or more than 5.07 g I ‘use a large mass’ alone I repeat and take mean I changes to heating e.g. heat for longer R more accurate balance or any other change to apparatus e.g. increase mass of crucible alone R incorrect use of weight for mass R heat to constant mass 1(e) M1 mol of Ca(NO ) in original sample = 0.5  0.0223 mol = 2 award 2 marks for 36.7 3 2 0.01115 mol A more SF e.g. 1.829715 g 36.741265% A 36.7 rounded to 37 for M2 I rounding errors after 3SF. M2 mass Ca(NO ) in original sample = 0.01115 mol  If M1 is rounded to 0.0112 mol and then used in M2 3 2 164.1 g mol–1 = 1.829715 g award M1 only % by mass Ca(NO ) = 1.829715 / 4.98  100% = 36.7% ecf for M2 from incorrect M1 and allow final answer to 3 2 be rounded to 2SF © Cambridge University Press & Assessment 2026 Page 8 of 13 Trace ID: PC-B8B10956DE 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/5a3 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/53 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(f)(i) heat to constant mass 1 A description of the process of heating to constant mass e.g. reheat and reweigh until mass remains constant A repeat steps 3 and 4 to constant mass response must include (re)heat and constant mass 1(f)(ii) The percentage by mass will be smaller. 1 A NO or O or both for gas 2 2 AND A amount / mol for mass mass of gas lost is smaller (than the maximum possible) OR I not all NO released 2 mass of solid remaining after heating is higher (than actual mass) I calculated mass of Ca(NO ) (that decomposes) is 3 2 lower than actual value 1(g) M1 attempted use of ice / cold water for condensing the gas 2 M1 A coolant/cool water for ice without loss of the NO as gas 2 If a condenser is seen, max 1 mark • must be angled downwards towards unsealed M2 in an unsealed collection vessel surrounded by iced / cold collection vessel water • must show water in and out of jacket • ignore position of water in and out • condensed NO must be delivered into a vessel 2 surrounded by ice/cold water. If a condenser is delivering into a u-tube and ice, then 2 marks can be awarded. © Cambridge University Press & Assessment 2026 Page 9 of 13 Trace ID: PC-B8B10956DE 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/5a3 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/53 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/

2(a) only (direct) light from the LED should be allowed to reach the 1 A to prevent outside light entering (the colorimeter) photocell A to prevent outside light reaching the photocell for outside light A external light / background light /surrounding light for photocell A detector A no (indirect) light via reflections A the only source of light is from the LED I other light for outside light I light absorbed unless it is absorbed by the photocell 2(b)(i) 1 Must be 3 DP concentration of resistance of absorbance, A I –(aq) / mol dm–3 photocell, R / k 3 s 3.60  10-6 34.28 0.839 2.94  10-6 23.42 0.684 2.20  10-6 16.01 0.519 1.52  10-6 9.68 0.300 7.90  10-7 7.50 0.189 2(b)(ii) distilled water (with few drops of starch solution) 1 A (acidified) I–(aq)/solution (with few drops of starch solution) A acidified I– ions (with few drops of starch solution) A I – solution/(aq) with no starch 3 2(b)(iii) concentration of I – 1 3 © Cambridge University Press & Assessment 2026 Page 10 of 13 Trace ID: PC-B8B10956DE 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/5a3 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/53 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(b)(iv) M1 all 5 points plotted correctly 2 Place plotting tick on grid above line of best fit. Place line tick in left-hand margin Place a cross beside an incorrect point M2 straight line of best fit through origin passing through or close ecf from 2(b)(i) to all points except anomaly (point 2) R if point 2 is on a vertical gridline R if point 4 is on a horizontal gridline R line of best fit that does not extend from the origin to cover all plotted points. R if line of best fit is one square or more from origin on either axis A line of best fit between the first and last (correctly plotted) points is acceptable as long as it goes close enough to the origin. All points except anomaly should be on the line of best fit. Point marked as anomalous (ringed) should not be used in determining the line of best fit. A ecf acceptable line of best fit drawn for incorrectly plotted points. R line of best fit if the points (except anomaly) not approximately evenly distributed on both sides of line I extra points added which are used in later calculations I remnants of lines that the candidate has tried to erase R curved line R double or “sketchy” lines. © Cambridge University Press & Assessment 2026 Page 11 of 13 Trace ID: PC-B8B10956DE 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/5a3 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/53 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(b)(v) most anomalous point circled 1 Expected answer is point 2 at (1.52  10–6, 0.300 below the line of best fit) AND A light intensity (in colorimeter) increased any one reason from: • not enough starch added (in step 2) A ora for ecf point above line of best fit • less than 10.0 cm3 solution transferred (from boiling tube to measuring cylinder in step 4) A light got into the colorimeter/black box not shut (no • solution (from step 2) was left for less than 10 minutes (in ora for point above line of best fit) step 3) I reading of absorbance was too low I comments about temperature/heat I starch not mixed properly I systematic error I evaporation I reference to rates 2(c)(i) to allow all the I – ions form a complex (with the starch) 1 A for complete reaction (of the I – ions and starch) 3 3 A enough time for the complex to form completely I to reach equilibrium I reference to rate of reaction I all the starch reacts 2(c)(ii) 10 cm3 volumetric pipette 1 A graduated pipette as long as volume is not < 10 cm3 A 10 cm3 pipette A volumetric pipette I ‘pipette’ alone R burette 2(c)(iii) M1 absorbance = 0.640 2 A 0.64 with working shown Concentration should be read from the graph to nearest ½ square. M2 concentration read from the graph to nearest ½ square and I any figures after 3SF given to 3 SF I trailing zeros (allow 2.7 for 2.70) A non-standard form 2.75  10–6 mol dm–3 is a common answer © Cambridge University Press & Assessment 2026 Page 12 of 13 Trace ID: PC-B8B10956DE 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/5a3 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/53 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(c)(iv) (15 / 1000)  2(c)(iii) 1 A 2 SF minimum A calculator value from 2(c)(iii) (e.g. 2.725 used for 2.73 given in 2(c)(iii)) I trailing zeros A non-standard form 2(c)(v) 2(c)(iv)  (1000 / 7500) 1 If using the given value, then: 3.23  10–8  1000 / 7500 = 4.31  10–9 mol dm–3 A calculator value from 2(c)(iv) A 2 SF minimum A non-standard form 2(c)(vi) increases 1 AND (the value of) the concentration of I – increases (at same 3 absorbance) 2(c)(vii) 9.87 + 0.14  9.87 = 11.25 AND 13.66 – 0.14  13.66 = 11.75 1 A any set of calculations which gives 11.25 and 11.75 AND the concentration of O is different (because the extremes of the 3 ranges do not overlap) 2(c)(viii) R increases 1 A light travels through a deeper solution s AND A light interacts with more I – particles 3 the light has a longer path length (through the solution) A absorbance increases with depth (of solution) I light interacts with more I – solution(aq) 3 I more light is absorbed alone I measuring cylinder is deeper 2(c)(ix) concentration of I – will be higher giving a lower percentage error 1 A amount / mol of I – for concentration of I – 3 3 3 I uncertainty for percentage error A uncertainty percentage error for percentage error alone © Cambridge University Press & Assessment 2026 Page 13 of 13 Trace ID: PC-B8B10956DE Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. 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1(a) (re)heat and (re)weigh to constant mass 1 A “heat to constant mass” A description of the process of heating to constant mass A “crucible and residue” or “sample” for “crucible and contents” R “heat to constant weight” 1(b)(i) (mass of Na CO •xH O(s) added / g =) 4.89 1 R any other values. 2 3 2 (mass of residue / g =) 2.06 AND (mass of water lost =) 2.83 1(b)(ii) increase the mass of Na CO •xH O(s) used 1 A use more (than 4.89 g / mass calculated in 1(b)(i) of) 2 3 2 Na CO •xH O(s) 2 3 2 A use of “amount” for “mass” A use of “solid” or “crystals” or “contents” or “reactant” or “sample” or “hydrated sodium carbonate” or “sodium carbonate crystals” for “Na CO •xH O(s)” 2 3 2 A increase the “mass of crucible and contents” I changes to heating I repeat and take mean R changing the crucible. e.g. increase the mass of crucible alone R “anhydrous sodium carbonate” / “sodium carbonate” alone / “powder” / Na CO for “Na CO •xH O (s)” 2 3 2 3 2 R incorrect use of “weight” for “mass” but A ecf from 1(a). R heat to constant mass © Cambridge University Press & Assessment 2026 Page 7 of 19 Trace ID: PC-3193057FA4 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/5a4 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/54 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(c) M1 n(H O) = 2.83 / 18 = (0.157(222)) 2 AND n(Na CO ) = 2.06 / 106 = (0.0194(34)) 2 3 M2 x = © Cambridge University Press & Assessment 2026 Page 8 of 19 n n ( N ( H a 2 2 O C O ) 3 ) 2 M1 A ecf from 1b(i) A rounding of amounts e.g. n(H O) = 0.16 and n(Na CO ) = 2 2 3 0.02 A valid alternative calculation routes M2 = (0.157 / 0.0194 = 8.09 → 8) A ecf from M1 if values used in M2 are calculated n(H O) and 2 n(Na CO ). 2 3 R non-integer value for x. e.g. 8.0 Trace ID: PC-3193057FA4 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/5a4 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/54 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(d)(i) M1 add a (small) volume of (distilled) water (to the small 3 A ‘solution' produced in M1 or M2 for “dissolve the solid”. beaker) A “solid disappears” for dissolves. AND A extra transfers as long as the exact number of moles of dissolve the solid / Na CO •xH O(s) solid end up in the volumetric flask via rinsing. (Allow greater 2 3 2 volume added when accommodated by vessel used.) A prepare / make a solution for dissolve. I use of measuring cylinder / stirring / glass rod I description of measuring mass / incorrect mass used R water volume > 50 cm3 if specified OR fill (50 cm3) beaker M2 A “rinse the beaker” or “wash the beaker” in place of Transfer the solution and washings (using a funnel) “washings” AND BOD assume rinsing and washing is of the beaker into the into a 250 cm3 volumetric flask. flask if not clearly indicated otherwise e.g. to wash the apparatus A 250 volumetric flask / 250 cm3 graduated flask / 250 cm3 standard flask A M2 If solid added directly to 250 cm3 volumetric flask AND beaker (+ funnel) are rinsed, and washings added to flask AND the solid dissolved in distilled / deionised water in flask before M3 I use of funnel / glass rod I rinse the volumetric flask (with (distilled) water)(before adding solid / solution) R transfer solution with burette or pipette R weighing solid into flask © Cambridge University Press & Assessment 2026 Page 9 of 19 Trace ID: PC-3193057FA4 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/5a4 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/54 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(d)(i) M3 Make up to the (calibration) mark / line (with distilled A ‘250 cm3 calibration’, ‘line’ or other similar for ‘mark’. ctd. water). A deionised water, DW, dH O, diH O for ‘distilled water’. 2 2 AND A make up to 250 cm3 (with distilled water). then invert (the stoppered flask) (several times) A ‘shake’, ‘swirl’ and ‘invert’ for ‘invert flask’. Must describe action, not ‘mix’ alone. A M2 and M3 if all correct except volume used to dissolve in M1 > 50 cm3 < 250 cm3 if specified. A use of pipette / burette to fill to mark. I top up / fill alone. I homogenise / mix R stir R M3 if solid not dissolved before making up to the mark. If purpose of inverting / shaking is to dissolve solid. A ecf M3 for volume > 250 cm3 (i.e. I volume from M1 and M2 when marking M3) M3 Distilled / deionised water only needs to be mentioned once to infer its use throughout. If not mentioned, then M3 not awarded. 1(d)(ii) (0.01(00) mol dm–3) hydrochloric acid / HCl((aq)). 1 A (rinse with the) solution to be used (for the titration in the burette) A dilute hydrochloric acid I wash with distilled water / propanone before wash with (0.0100 mol dm-3) HCl R wash with distilled water / propanone after wash with (0.0100 mol dm-3) HCl © Cambridge University Press & Assessment 2026 Page 10 of 19 Trace ID: PC-3193057FA4 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/5a4 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/54 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(e)(i) (it is calculated from) titrations 1 and 3 1 A titrations 1 and 3 (are used), which are within 0.1(0) (cm³) of each other / are ±0.1(0) (cm3) AND A the difference between titres 1 and 3 is 0.1(0) (cm³) A the difference between titres 1 and 3 is equal or less than which are concordant. 0.1(0) (cm³) A the difference between titres 1 and 3 is within 0.1(0) (cm³) (of each other) A values for titrations 1 and 3. e.g. 25.25 and 25.15 A values clearly indicated and annotated in Table 1.1 I mention of not using titration 2 R if titration 2 is used 1(e)(ii) M1 n(HCl) in mean titre= 0.0252  0.0100 4 A ecf throughout = 2.52  10–4 (mol) A valid alternative calculation routes M2 n(Na CO ) in 25.0 cm3 of solution 2 3 = (2.52  10-4 ÷ 2) = 1.26  10–4 (mol) M3 n(Na 2 CO 3 ) in 250.0 cm3 of solution M3 A m(Na 2 CO 3 ) in 0.365 g = 1.26  10–4  10  106 = 1.26  10–4  10 = 1.26  10–3 (mol) = 0.134 g M (Na CO •xH O) = 0.365 / 1.26  10–3 = 289.68 m(H 2 O) = 0.365 – 0.134 = 0.231 g r 2 3 2 n(H O) = 0.231 / 18 = 0.012858 2 M4 x = (289.68 – 106) / 18 = 10.20 → 10 M4 x= 0.012858 / 1.26  10–3 = 10.20 → 10 A ECF for M4 if values used are calculated n(H 2 O) and n(Na 2 CO 3 ). Missing factor of 10 in M3 leads to x = 155. M4 still available. M4 R non-integer value for x, but A ecf from e.g. 8.0 in 1(c) for e.g.10.0. Missing ÷ 2 in M2 leads to x = 2. M3 and M4 still available. © Cambridge University Press & Assessment 2026 Page 11 of 19 Trace ID: PC-3193057FA4 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/5a4 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/54 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 1(e)(iii) correct working must be shown 1 2 × ( ½ × 0.10) A  100 = 0.3976 25.15 2 × 0.05 maximum percentage error =  100 = 0.3976(14) 0.05 + 0.05 25.15 A  100 = 0.3976 25.15 A the following values for the answer following a correct expression – 0.4, 0.40, 0.39, 0.397 etc I missing  100 if correct answer given R incorrectly calculated answer with correct working R (0.005  2 / 25.15)  100 = 0.0398 1(f) (effect on value of =) increases 1 A ‘higher’ or ‘greater’ or ‘overestimated’ for ‘increases’ etc A “decreases” or “smaller” or “underestimated” for “lower” AND etc A ‘sodium carbonate’ or ‘Na CO •xH O(s)’ for ‘Na CO ’ 2 3 2 2 3 n(Na CO ) is lower OR n(H O) is greater (than true value). A ‘number of moles’ or ‘mole number’ or ‘amount’ for n 2 3 2 I powder / crystals I measured volume of solution A / Na CO (aq) is less 2 3 OR I recorded volume of solution A / Na CO (aq) is larger 2 3 (effect on value of x =) no / negligible effect A ‘slight increase’ for ‘negligible’ AND value of x is to the nearest integer so (small) change in volume does not affect value

2(a)(i) n(NH Cl) = 5.00 / 53.5 = 0.0935 1 R any answer other than 3.46 g 4 mass of Ca(OH) = 0.0935 / 2  74.1 = 3.46 g 2 © Cambridge University Press & Assessment 2026 Page 12 of 19 Trace ID: PC-3193057FA4 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/5a4 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/54 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(a)(ii) hazardous gas (ammonia) produced 1 A toxic / corrosive / irritant for ‘hazardous’ I flammable I bad smell I harmful / dangerous / ’harmful to health’ I alkaline 2(a)(iii) to remove water (vapour) (from (ammonia) gas) 1 A to absorb water (from gas) A to avoid water passing into gas jar A to dry (the gas) A to ensure (ammonia) gas does not contain water I to flush any air out of the tube. I dehydrate / dehydration I to purify I to prevent ammonia dissolving in water. I ‘CaO reacts with water’ alone (no reference to removing water) (no mark – to make sure only ammonia reaches the gas jar) R to remove chlorine R to react with ammonia R “to dry water” alone 2(a)(iv) ammonia is less dense than (most gases in) air 1 A ‘NH ’for ‘ammonia’ 3 A “ammoniaisless dense than oxygen and nitrogen” A “ammonia has a smaller density than (most gases in) air” A ammonia has a smaller M than mean M for air r r I ‘lighter’ I it will displace the air I atmosphere I ‘less dense than oxygen alone or nitrogen alone’ R less dense than any other named gas. e.g. chlorine © Cambridge University Press & Assessment 2026 Page 13 of 19 Trace ID: PC-3193057FA4 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/5a4 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/54 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(b) ammonia is soluble (in water) 1 A ‘NH ’for ‘ammonia’ 3 A ammonia would react with water A correct species in balanced equation for reaction of ammonia with water, ignore state symbols (allow =, → or ⇌) e.g. NH + H O ⇌ NH + + OH− 3 2 4 A suck back could occur A ammonia would / can / will dissolve (in the water) I incorrect reaction equations, products etc © Cambridge University Press & Assessment 2026 Page 14 of 19 Trace ID: PC-3193057FA4 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/5a4 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/54 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(c)(i) M1 all six points plotted correctly 2 M1 If point should be on a line, it must be on the line. If it should not be on the line, it must not be so. Blobs/thick crosses should be less than ½ a small square across and be correctly centred. M1 not awarded if centre of at least one cross is clearly off a line it should be on, on a line it should not be or in the wrong small grid square. Note: Other points are correctly plotted. If not clearly plotted at a different y value, assume point at 0s is present and obscured by the point at same time for tungsten. (In this case there is no need to check for this point). M2 M2 line of best fit drawn A ecf acceptable best fit line drawn for incorrectly plotted points I remnants of lines that have been rubbed out R double or “sketchy” lines. R line that does not extend across full range of x-values for plotted points. (A ½ small square tolerance at each end) 2(c)(ii) [NH ] (in mol dm–3) 1 A ‘concentration of ammonia’ or ‘concentration of NH ’ for 3 3 ‘[NH ]’ 3 A [NH ] / mol dm–3 3 I type of catalyst © Cambridge University Press & Assessment 2026 Page 15 of 19 Trace ID: PC-3193057FA4 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/5a4 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/54 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(d)(ii) there are no anomalous results 1 A there are no points off the line (of best fit) A (all) the points are (very) close to / on the line (of best fit) A (straight) line passes through / touching (all) points R (straight) line passing all points A “outliers” for “anomalous results” A “anomalous” to mean “anomaly” or “anomalous result” A “plots” for “points” I the line fits the data I “values” for “points” I most points are on / close to the line of best fit 2(d)(iii) yes (it does support the student’s conclusion) 1 A inferred agreement with student e.g. saying the reaction is zero order AND R no, (it does not support the student’s conclusion) (the line has) constant gradient A the line is straight A the graph / line is linear A t decreases (with time) ½ A rate (of decrease of [NH ]) is constant (over the time 3 period shown by the graph)(at a particular temperature) A [NH ] has a linear relationship with time 3 © Cambridge University Press & Assessment 2026 Page 16 of 19 Trace ID: PC-3193057FA4 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/5a4 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/54 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(e) For straight line of best fit: ctd. M1 any two different points from line of best fit correctly recorded (x ,y ) and (x ,y ). 1 1 2 2 Can be awarded it is clear an attempt has been made to calculate a gradient. M2 Calculates gradient of line correctly. (y -y ) / (x -x ) 2 1 2 1 AND Calculates t correctly using gradient and y = mx + c to work ½ out value of x (t ) at half value of y (y at t=0). ½ 0 t = ((y / 2) – c) /m ½ 0 For a curved line of best fit: M1 any two different points from line of best fit correctly recorded (x ,y ) and (x ,y ). 1 1 2 2 Can be awarded if a clear attempt has been made to use calculation below. M2 states “assuming first order” owtte AND half-life correctly calculated as follows: calculate 𝑘 using coordinates from line of best fit ln(y1/ y2) k = x2−x1 expected value k 1.4110−3 s−1 for a first-order reaction: © Cambridge University Press & Assessment 2026 Page 18 of 19 t1 /2 = 0 . 6 k 9 3 Tolerance x value ± half a square (10 s) from stated y-value. A coordinates 1 and 2 recorded in either order M2 A ecf for correctly evaluated t from points on line of best ½ fit if only error in M1 is that one of the x values has been incorrectly read from graph. M2 A ecf correctly evaluated t from otherwise correct LOBF ½ points both written (y, x) M2 A ecf for minor slip in recording correct coordinates. e.g. missing  10–3 (M1 not awarded) No ecf M2 if any two mistakes made in recorded coordinates R negative value for M2 expected value t = 491 s approx. ½ Trace ID: PC-3193057FA4 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/5a4 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/54 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 2(f) (four half-lives: 4  550 =) 2200 s 1 © Cambridge University Press & Assessment 2026 Page 19 of 19 Trace ID: PC-3193057FA4 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/5a4 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9701/54 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/