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Practical skills: planning, analysis and evaluation

Past-paper questions pack

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Questions are numbered; the mark schemes (the answer key) follow on separate pages so the question pages can be handed out alone. www.chemistryaleveltutor.com

OCR AS and A-level Chemistry past-paper questions since 2016 · 96 parts · mark schemes follow the questions · www.chemistryaleveltutor.com · Questions and mark schemes © OCR

1. June 2025 · AS Paper 1 · Q1 · 1 marks ·
1 The burette readings from a titration are shown below. Initial reading / cm3 4.95 Final reading / cm3 23.10 The burette used has an uncertainty of 0.05 cm3 for each reading. What is the percentage uncertainty of the resulting titre? A 0.22% B 0.28% C 0.44% D 0.55% Your answer [1]
2. June 2025 · Paper 1 · Q8 · 1 marks ·
8 The burette readings from an experiment are shown: Final reading / cm3 29.35 Initial reading / cm3 2.60 The burette has an uncertainty of ±0.05 cm3. What is the percentage uncertainty of the titre? A 0.17% B 0.19% C 0.34% D 0.37% Your answer [1]
3. June 2025 · Paper 1 · Q18(c)(ii) · 4 marks ·
(ii) Plot a graph of ln k against 1 T on the grid opposite. Use your graph to calculate the value of the activation energy, Ea, in kJ mol–1. Give your answer to 2 significant figures. Ea = ............................................ kJ mol–1 [4]
4. June 2025 · AS Paper 2 · Q2(b)(ii) · 2 marks ·
(ii) The volume of gas collected is less than the calculated volume. Suggest two reasons for this difference. 1 ....................................................................................................................................................... .......................................................................................................................................................... 2 ....................................................................................................................................................... .......................................................................................................................................................... [2]
5. June 2025 · AS Paper 2 · Q2(b)(iii) · 1 marks ·
(iii) Suggest one way in which the student could modify the apparatus to produce a volume closer to the calculated volume. .......................................................................................................................................................... ..................................................................................................................................................... [1]
6. June 2025 · AS Paper 2 · Q3(b) · 2 marks ·
(b) Another student carries out the same experiment. Instead of rinsing the burette used in Step 4 with 0.0800 mol dm–3 NaOH, the student rinses with water before filling it up with 0.0800 mol dm–3 NaOH. State and explain how this error would affect the titre. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [2]
7. June 2025 · Paper 2 · Q19(b)(ii) · 4 marks ·
(ii) The reaction to form 1-bromopropane from propan-1-ol is carried out in a flask. After the reaction, the flask contains a mixture of an organic layer (density = 1.35 g cm–3) and an aqueous layer (1.04 g cm–3). Describe how to obtain pure 1-bromopropane from the mixture. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [4]
8. June 2025 · Paper 3 · Q3(a) · 5 marks ·
3 This question is about equilibrium and rates. (a) Methanol, CH3OH, can be made industrially by the reaction of carbon monoxide, CO, with hydrogen, H2, in the presence of a catalyst. This is a reversible reaction. The equilibrium below is set up. CO(g) + 2H2(g) CH3OH(g) ∆H = –91 kJ mol–1 The concentrations of CO(g) and CH3OH(g) in the equilibrium mixture are shown in the table below. CO(g) CH3OH(g) equilibrium concentration / mol dm–3 0.27 0.11 The value of the equilibrium constant, Kc, for this reaction is 1.8 dm6 mol–2. • Explain the conditions of pressure and temperature that would give the maximum equilibrium yield of CH3OH(g). • Calculate the concentration of H2(g) in the equilibrium mixture to an appropriate number of significant figures. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [5]
9. June 2024 · Paper 1 · Q19(b)(i) · 5 marks ·
(b) A student titrates a 10.0 cm3 sample of ethanoic acid, CH3COOH, against an aqueous solution of 0.0560 mol dm–3 Ba(OH)2. 2CH3COOH + Ba(OH)2 Ba(CH3COO)2 + 2H2O The student used a pH meter to measure the pH of the mixture after every addition of Ba(OH)2 throughout the titration. The student’s results are shown below. 12 11 10 9 8 7 pH 6 5 4 3 2 1 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 volume of Ba(OH)2 / cm3 (i) Draw a best-fit curve on the graph and calculate the concentration of the CH3COOH solution. CH3COOH concentration = .......................................... mol dm–3 [5]
10. June 2024 · AS Paper 1 · Q22(b)(i) · 1 marks ·
(b) Ethanoic acid, CH3COOH, is found in some descalers to soften hard water. A student carries out a titration with a standard solution of sodium carbonate, Na2CO3, to determine the percentage composition by mass of CH3COOH in a descaler. The equation is shown below. 2CH3COOH + Na2CO3 2CH3COONa + CO2 + H2O (i) The method is outlined below: • Dissolve 6.50 g of the descaler in distilled water. • Transfer the solution into a 250.0 cm3 volumetric flask. • Make up to the mark with distilled water and invert several times. • Pipette 25.0 cm3 of this solution into a conical flask and add a few drops of indicator. • Titrate this solution with 0.200 mol dm–3 Na2CO3(aq), in the burette. The student carries out a trial titration, followed by further titrations. The results are shown in the table below. The trial titration has been omitted. Titration 1 2 3 Final reading / cm3 48.95 24.15 48.35 Initial reading / cm3 24.55 0.00 24.10 Titre / cm3 Complete the table by adding the titres. [1]
11. June 2024 · AS Paper 2 · Q3(b) · 6 marks ·
(b)* A student carries out an experiment to determine the enthalpy change for the reaction between zinc and copper(II) nitrate solution. Zn(s) + Cu(NO3)2(aq) Zn(NO3)2(aq) + Cu(s) ΔrH Equation 3.1 The student follows the method outlined below. • Add 100 cm3 of 0.500 mol dm–3 Cu(NO3)2(aq) to a beaker. • Measure the temperature of the solution. • Add excess zinc to the beaker. • Stir the mixture and record the maximum temperature. The temperature of the solution changes from 19.5 °C to 38.1 °C. Calculate ΔrH, in kJ mol–1, for equation 3.1. State any assumptions you have made in your calculation. Suggest improvements for obtaining a more accurate value for ΔrH. [6] .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... 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12. June 2024 · AS Paper 2 · Q4(b)(i) · 2 marks ·
(b) A student investigates the rate of decomposition of H2O2, on addition of MnO2 catalyst, using a gas syringe. 100 cm3 gas syringe The student obtains the results shown in graph 4.1. Graph 4.1 100 90 80 70 60 Volume 50 / cm3 40 30 20 10 0 0 20 40 60 80 100 120 140 160 180 200 Time / s (i) On graph 4.1, draw a best-fit smooth curve of the results and circle the anomalous result. [2]
13. June 2024 · AS Paper 2 · Q4(c) · 2 marks ·
(c) A student plans to compare the rate of decomposition of H2O2 using different metal oxides as the catalyst. Suggest two variables which should be kept constant. 1 ....................................................................................................................................................... 2 ....................................................................................................................................................... [2]
14. June 2024 · Paper 2 · Q23(b)(ii) · 1 marks ·
(ii) Another student suggests that adding aqueous sodium hydroxide would be more effective in removing the sulfuric acid catalyst than Na2CO3(aq). Comment on whether the student’s suggestion is an improvement for the preparation of compound H. .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [1]
15. June 2024 · Paper 3 · Q3(b)(ii) · 3 marks ·
(ii) The student prepares a 250.0 cm3 solution of iron(II) ethanedioate by dissolving 1.295 g of FeC2O4•xH2O, in dilute sulfuric acid. The student titrates 25.0 cm3 samples of this solution with 0.0200 mol dm−3 KMnO4 in the burette. The student carries out a trial, followed by three further titrations. The diagrams show the initial burette readings and the final burette readings for the student’s three further titrations. Titration 1 Titration 2 Titration 3 Initial reading Final reading Initial reading Final reading Initial reading Final reading 0 23 23 45 0 21 1 24 24 46 1 22 2 25 25 47 2 23 All burette readings are measured to the nearest 0.05 cm3. Complete the titration table. 1 2 3 Final reading / cm3 Initial reading / cm3 Titre / cm3 [3]
16. June 2024 · Paper 3 · Q3(b)(iii) · 1 marks ·
(iii) The uncertainty in each burette reading is ±0.05 cm3. Calculate the percentage uncertainty for the titre in Titration 1. percentage uncertainty = .................................................... % [1]
17. June 2023 · Paper 1 · Q18(c)(ii) · 5 marks · AO3
(ii) Reaction 2 is repeated: C2H5OH(g) C2H4(g) + H2O(g) Reaction 2 The Gibbs equation is shown below. ∆G = ∆H – T∆S The enthalpy change, ∆H, and the entropy change, ∆S, can be assumed to be constant at different temperatures. Fig. 18.1 shows values of the free energy change, ∆G, in kJ mol–1, at different temperatures, T, in K, for Reaction 2. Fig. 18.1 60 50 40 30 20 10 ∆G 0 / kJ mol–1 –10 –20 –30 –40 –50 –60 0 100 200 300 400 500 600 700 800 900 T / K Use the graph in Fig. 18.1 to answer the following: • Draw the best-fit line on the graph in Fig. 18.1. • Determine ∆S, in J K–1 mol–1, for Reaction 2. • Determine the minimum temperature, T, at which the reaction is feasible. • Determine ∆H for Reaction 2. ∆S = .................................... J K–1 mol–1 minimum T = ....................... K ∆H = .................................... kJ mol–1 [5]
18. June 2023 · Paper 1 · Q21(a)(ii) · 2 marks · AO2
(ii) The student’s titration results are shown in the table below. The trial titre has been omitted. 1 2 3 Final volume / cm3 12.65 25.60 38.35 Initial volume / cm3 0.00 12.65 25.60 Titre volume / cm3 Complete the table above and calculate the mean titre that the student should use to determine the concentration of iron(II) ions in the river water. mean titre = .................................................. cm3 [2]
19. June 2023 · Paper 1 · Q21(b) · 4 marks · AO3
(b) The student modifies the experiment in (a) to determine the combined concentration of iron(II) and iron(III) ions in the river water. The student’s method is shown below. Step 1 Add excess zinc to a 250.0 cm3 sample of river water and warm gently. Step 2 Cool the solution and remove excess zinc by filtration. Step 3 Acidify 25.0 cm3 portions of the filtrate from Step 2. Then titrate each portion with 0.00250 mol dm–3 potassium manganate(VII) until a colour change is seen. The table below shows information about three redox systems. Redox system Half-equation E ө / V 1 Zn2+(aq) + 2e– Zn(s) –0.76 2 Fe3+(aq) + e– Fe2+(aq) +0.77 3 MnO4 –(aq) + 8H+(aq) + 5e– Mn2+(aq) + 4H2O(l) +1.51 Use the information in the table above to explain the reasons for Step 1 and Step 2. Reason(s) for Step 1 ................................................................................................................ ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... Reason(s) for Step 2 ................................................................................................................ ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... [4]
20. June 2023 · AS Paper 1 · Q22(c)(ii) · 1 marks · AO1
(ii) The student takes burette readings to the nearest 0.05 cm3. The student’s readings are shown in the table. The rough titre has been omitted. Complete the table below. Final reading 20.25 40.85 25.85 / cm3 Initial reading 0.00 20.25 5.50 / cm3 Titre / cm3 ................................ ................................ ................................ [1]
21. June 2023 · AS Paper 2 · Q1(b)(iii) · 2 marks · AO3
(iii) Reaction 1.2 produces a mixture of titanium and sodium chloride. Suggest how titanium could be separated from this mixture at room temperature. Explain your answer. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
22. June 2023 · AS Paper 2 · Q2(b)(ii) · 4 marks · AO3
(ii) The student obtains 3.28 g of precipitate. Calculate the percentage by mass of NaCl (s) in the 5.00 g mixture. Give your answer to 3 significant figures. percentage by mass of NaCl (s) = ...................................................... % [4]
23. June 2023 · AS Paper 2 · Q2(b)(iii) · 2 marks · AO3
(iii) The student changes the method in 2(b). In step 2, the student adds an excess of silver nitrate solution, AgNO3(aq), instead of Na2SO4(aq). Explain whether this change would allow the student to determine the percentage by mass of NaCl (s) in the mixture. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
24. June 2023 · AS Paper 2 · Q4(b)(i) · 1 marks · AO2
(b) A student carries out an experiment to determine the enthalpy change of combustion, ΔcH, of butan-1-ol, CH3CH2CH2CH2OH. The student sets up the apparatus as shown below. thermometer beaker clamp 200 g water wick spirit burner butan-1-ol The student’s results are shown in the table below. Initial temperature of water / °C 18.5 Final temperature of water / °C 49.5 Mass of burner before heating / g 212.38 Mass of burner after heating / g 211.07 (i) The thermometer had an uncertainty of ± 0.25 °C in each temperature reading. Calculate the percentage uncertainty in the temperature change. percentage uncertainty = ...................................................... % [1]
25. June 2023 · AS Paper 2 · Q4(b)(ii) · 6 marks · AO2, 3
(ii)* Use the student’s results to determine ∆cH of butan-1-ol in kJ mol–1. Explain why this value of ΔcH is different from the data book value and suggest how the experimental design could be modified to improve the accuracy of the ΔcH value obtained. [6] ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... Additional answer space if required. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...........................................................................................................................................
26. June 2023 · Paper 3 · Q4(b)(ii) · 1 marks · AO3
(ii) In Step 3, why does the student allow the solvent to evaporate and not boil off all the solvent in Step 2? ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [1]
27. June 2022 · Paper 1 · Q17(a)(ii) · 1 marks · AO3
(ii) The student wants to repeat the experiment, but there is not enough AgNO3(aq) left to use another 100.0 cm3 portion. The student decides to modify the method by adding an excess of magnesium to 50.0 cm3 of 0.400 mol dm–3 AgNO3(aq). Predict, with reasons, how this modification would affect the maximum temperature reached. Assume that there are no heat losses. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [1]
28. June 2022 · Paper 1 · Q19(a)(i) · 2 marks · AO1
19 This question is about acids and buffer solutions. (a) Succinic acid, HOOC(CH2)2COOH, is a weak dibasic acid that is used in tablet form in health supplements. A student plans to determine the mass of succinic acid in one tablet of a succinic acid health supplement. The student carries out a titration with potassium hydroxide. The end point occurs when both acidic protons in succinic acid have been replaced as shown in Equation 19.1. HOOC(CH2)2COOH + 2KOH KOOC(CH2)2COOK + 2H2O Equation 19.1 The student uses the following method. Stage 1 The student crushes four tablets of the health supplement and dissolves the powdered tablets in distilled water. Stage 2 The student makes up the solution from Stage 1 to 250.0 cm3 in a volumetric flask. Stage 3 The student titrates 10.0 cm3 portions of the solution obtained in Stage 2 with 0.0600 mol dm–3 potassium hydroxide, using phenolphthalein as the indicator. The student carries out a trial titration, followed by three further titrations. The results are shown below. Titration Trial 1 2 3 Final burette reading / cm3 25.25 23.75 25.35 25.75 Initial burette reading / cm3 2.50 1.30 2.65 3.20 Titre / cm3 (i) Complete the table and calculate the mean titre that the student should use for analysing the results. mean titre = .................................................. cm3 [2]
29. June 2022 · AS Paper 1 · Q24(b) · 5 marks · AO3
(b) A student is supplied with aqueous solutions of ionic compounds B and C. Compound B is a chloride, bromide or iodide of a Group 1 element. Compound C is a chloride, bromide or iodide of a Group 2 element. The molar masses of B and C are both in the range 100–115 g mol–1. Use this information and test-tube tests to show how the student could identify the halide present in B and C and the formulae of B and C. Explain your reasoning. In your answer, include observations, colours and equations. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [5]
30. June 2022 · AS Paper 2 · Q1(c) · 2 marks · AO3
(c) The student’s teacher thinks that there is an unnecessary safety risk in using a sodium hydroxide concentration of 0.800 mol dm–3 for the titration. Suggest how the student could modify the method using a sodium hydroxide concentration of 0.200 mol dm–3 instead of 0.800 mol dm–3. The student should aim to have the same titre as in the original method. Justify your answer. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [2]
31. June 2022 · AS Paper 2 · Q3(a)(ii) · 2 marks · AO3
(ii) Using the graph in Fig. 3.1, find the rate of reaction, in g s–1, at 50 seconds. Show your working on the graph and in the space below. rate of reaction = ................................................. g s–1 [2]
32. November 2021 · Paper 1 · Q18(e)(i) · 1 marks · AO3
(e) Explain whether the calculated percentage by mass of copper would be higher, lower or the same if the following changes were made to the method. (i) The potassium iodide was not in excess, in Step 3. ........................................................................................................................................... ...................................................................................................................................... [1]
33. November 2021 · Paper 1 · Q18(e)(ii) · 1 marks · AO3
(ii) The burette readings were read from the top of the meniscus, in Step 4. ........................................................................................................................................... ...................................................................................................................................... [1]
34. November 2021 · Paper 1 · Q18(f) · 2 marks · AO3
(f) The student then modifies the method in order to obtain a more accurate value for the percentage by mass of copper in the ore. The student decides to use 25.00 g of the copper ore in Step 1. What further modifications should the student make to produce a more accurate value for the percentage by mass of copper in the ore? ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [2]
35. November 2021 · AS Paper 1 · Q23(d) · 5 marks · AO1, 2, 3
(d) A student investigates the trend in reactivity of the halogens Cl 2, Br2 and I2. The student is supplied with: • solutions of Cl 2, Br2 and I2 in cyclohexane (an organic solvent) • aqueous solutions of the halides: NaCl , NaBr and NaI. The colours of the halogen solutions in cyclohexane are shown below. Halogen Cl 2 Br2 I2 Colour in cyclohexane Pale green Orange Violet Plan an experiment on a test tube scale that would show the trend in the reactivity of the halogens Cl 2, Br2 and I2. Include all the expected observations and an ionic equation for one of the reactions. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [5]
36. November 2021 · AS Paper 1 · Q25(a)(ii) · 1 marks · AO3
(ii) The student was unsure that all of the scandium had reacted. Suggest one modification that the student could make to their method to be confident that all the scandium had reacted. Explain your reasoning. ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [1]
37. November 2021 · AS Paper 2 · Q3(b)(i) · 1 marks · AO2
(b) The student carries out a trial titration followed by three further titrations, 1, 2 and 3. The results are shown in the table below. Titration Trial 1 2 3 Final reading / cm3 18.70 36.55 18.30 36.60 Initial reading / cm3 0.20 18.50 0.10 18.30 Titre / cm3 (i) Complete the table to show the titre in each titration. [1]
38. November 2021 · AS Paper 2 · Q3(b)(iii) · 1 marks · AO2
(iii) Calculate the mean titre of NaOH(aq) that the student should use for analysing the results. mean titre = .................................................. cm3 [1]
39. November 2021 · AS Paper 2 · Q3(b)(iv) · 1 marks · AO2
(iv) In the titration, the uncertainty in each burette reading is ± 0.05 cm3. Calculate the percentage uncertainty in the titre for Titration 1. percentage uncertainty = ..................................................... % [1]
40. November 2021 · AS Paper 2 · Q3(d) · 2 marks · AO3
(d) A 25.0 cm3 pipette was used to measure out the 25.0 cm3 of glutaric acid solution for each titration. Before use, one student washed the pipette out with water instead of the glutaric acid solution. State the effect of this mistake on the titre. Explain your answer. Effect ......................................................................................................................................... Explanation ............................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... [2]
41. November 2021 · AS Paper 2 · Q6(a) · 3 marks · AO1, 2
6 A student investigates the rate of reaction between strontium and water. Sr(s) + 2H2O(l) Sr(OH)2(aq) + H2(g) The student’s method is shown below. • Pour 100 cm3 of water into a conical flask. • Add 0.26 g of strontium and quickly connect a 100 cm3 gas syringe. • Measure the volume of gas produced every 10 seconds until all the strontium has reacted. The student plots a graph of volume of gas produced against time as shown in Fig. 6.1. 80 70 60 50 volume of gas 40 produced / cm3 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 time / s Fig. 6.1 (a) Draw a best fit curve on Fig. 6.1. Use the graph to determine the rate of reaction, in cm3 s–1, at 50 s. Show your working below and on the graph. rate at 50 s ............................................. cm3 s–1 [3]
42. November 2021 · AS Paper 2 · Q6(b) · 2 marks · AO3
(b) A second student suggests that the experiment could be improved by measuring the loss in mass in the conical flask over time. The student places a conical flask containing 100 cm3 of water on a 2 decimal place balance, and then adds 0.26 g of strontium. The mass is recorded every 10 seconds. Suggest one advantage and one disadvantage of using this method compared to the gas collection method. Advantage: ............................................................................................................................... ................................................................................................................................................... Disadvantage: ........................................................................................................................... .............................................................................................................................................. [2]
43. November 2021 · Paper 3 · Q2(a) · 2 marks · AO3
2 Europium (Ar = 152.0) reacts with dilute aqueous acid in a redox reaction, forming a solution and hydrogen gas. A student proposed three possible ionic equations for this reaction, forming europium ions with different charges: Equation 1 2Eu(s) + 2H+(aq) 2Eu+(aq) + H2(g) Equation 2 Eu(s) + 2H+(aq) Eu2+(aq) + H2(g) Equation 3 2Eu(s) + 6H+(aq) 2Eu3+(aq) + 3H2(g) The student plans to carry out an investigation to determine which equation is correct. Hydrochloric acid is used as the source of H+(aq) ions. The student’s method is outlined below. Step 1 Using a 3 decimal place balance, weigh a suitable container for the reaction. Add about 1 g of europium to the container and reweigh. Step 2 Set up apparatus for gas collection. Add an excess of dilute hydrochloric acid to the europium. Step 3 Measure the volume of gas produced. Results Mass of container = 32.795 g Mass of container + europium = 33.783 g Volume of gas collected = 152 cm3 (a) Draw a labelled diagram of suitable apparatus for this investigation. [2]
44. November 2021 · Paper 3 · Q2(b) · 3 marks · AO2, 3
(b) Analyse the student’s results to conclude which of Equation 1 or 2 or 3, is supported by the experimental results. Assume that the conditions in the laboratory are ‘room temperature and pressure’ (RTP). correct equation (1, 2, or 3) = ................ [3]
45. November 2021 · Paper 3 · Q2(c) · 2 marks · AO3
(c) The student repeats the experiment but adds concentrated hydrochloric acid instead of dilute hydrochloric acid. The apparatus gets hot during the reaction. Predict how the hot apparatus would change the student’s results and the conclusion in (b). Explain your answer. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [2]
46. November 2021 · Paper 3 · Q2(d) · 2 marks · AO3
(d) The student modifies their method as outlined below: • 1.52 g (0.01 mol) of europium is reacted with an excess of dilute hydrochloric acid. • An excess of aqueous sodium hydroxide is added to the reaction mixture. • A precipitate forms which is collected, dried and weighed. Explain how the mass of precipitate formed would allow the student to conclude which of Equation 1 or 2 or 3 is correct. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [2]
47. November 2021 · Paper 3 · Q4(c)(ii) · 2 marks · AO3
(ii) Suggest how the investigation could be modified to show that the reaction is first order with respect to pent-1-ene. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
48. November 2020 · Paper 1 · Q1 · 1 marks · AO2
1 Several students titrate 25.00 cm3 of the same solution of sodium hydroxide, NaOH(aq) with hydrochloric acid, HCl (aq). One student obtains a smaller titre than the other students. Which procedure explains the smaller titre? A The burette readings are taken from the top of the meniscus instead of the bottom of the meniscus. B The conical flask is rinsed with water before carrying out the titration. C An air bubble is released from the jet of the burette during the titration. D The pipette is rinsed with water before filling with NaOH(aq). Your answer [1]
49. November 2020 · Paper 1 · Q20(a)(i) · 1 marks · AO3
20 A student investigates the reaction between ethanoic acid, CH3COOH(l) and methanol, CH3OH(l), in the presence of an acid catalyst. The equation is shown below. CH3COOH(l) + CH3OH(l) CH3COOCH3(l) + H2O(l) (a) The student carries out an experiment to determine the order of reaction with respect to CH3COOH. The student uses a large excess of CH3OH. The temperature is kept constant throughout the experiment. The student takes a sample from the mixture every 20 minutes, and then determines the concentration of the ethanoic acid in each sample. From the experimental results, the student plots the graph below. 5.0 [CH3COOH] /10–3 mol dm–3 4.0 3.0 2.0 1.0 0 20 40 60 80 100 120 140 160 180 time / min (i) Explain why the student uses a large excess of methanol in this experiment. ........................................................................................................................................... ...................................................................................................................................... [1]
50. November 2020 · AS Paper 1 · Q23(c) · 4 marks · AO2, 3
(c) A student plans to prepare a solution of Ba(OH)2 from barium by two different reaction routes. Outline 2 reaction routes for preparing a solution of Ba(OH)2 from barium in the laboratory. Include relevant equations. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [4]
51. November 2020 · AS Paper 2 · Q2(c)(i) · 2 marks · AO2
(c) The student finds that their experimental value for ΔcH is less exothermic than the value in a data book. The student evaluates the experimental results. (i) The uncertainty in each thermometer reading is ±0.5 °C and the uncertainty in the measured volume of water is ±2 cm3. Determine whether the temperature change or the measured volume of water has the greater percentage uncertainty. [2]
52. November 2020 · AS Paper 2 · Q2(c)(ii) · 2 marks · AO3
(ii) Suggest two reasons, apart from measurement uncertainties, why the experimental value for ΔcH is less exothermic than the data book value. Reason 1 ............................................................................................................................ ........................................................................................................................................... Reason 2 ............................................................................................................................ ........................................................................................................................................... [2]
53. November 2020 · AS Paper 2 · Q2(c)(iii) · 2 marks · AO3
(iii) In the experiment the water in the beaker was heated for 5 minutes. The student thought that the experiment could be improved by heating the water for 10 minutes. Explain whether the accuracy in the student’s calculated value for ΔcH may or may not be improved by heating for longer. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
54. November 2020 · Paper 3 · Q3(a)(ii) · 1 marks · AO1
(ii) The student finds that the experimental enthalpy change ∆cH (C3H8) is much less exothermic than the accurate standard enthalpy change ∆cH (C3H8) in databases. One reason could be that the student’s experiment had not been carried out under standard conditions. Suggest two other reasons for this difference in enthalpy change. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... [1]
55. November 2020 · Paper 3 · Q4(c)(i) · 1 marks · AO3
(c) After analysing the results, the student was told that their molar mass of X2CO3 was incorrect. The student evaluated the experiment for possible reasons for the incorrect result. (i) The student wondered whether the reaction was complete when the mass was recorded after 5 minutes (Step 3). How could the student modify the experimental procedure to be confident that the reaction was complete? ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [1]
56. November 2020 · Paper 3 · Q4(c)(ii) · 2 marks · AO3
(ii) The student finds out that carbon dioxide is slightly soluble in water. State and explain how the solubility of CO2 would affect the calculated molar mass of X2CO3. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
57. November 2020 · Paper 3 · Q5(a) · 2 marks · AO1
5 The equilibrium constant Kp and temperature T (in K) are linked by the mathematical relationship shown in equation 5.1 (R = Gas constant in J mol−1 K−1 and ∆H is enthalpy change in J mol−1). ln Kp = – ∆H R × 1 T + ∆S R Equation 5.1 (a) The table shows the values of Kp at different temperatures for an equilibrium. Complete the table by adding the missing values of 1 T and ln Kp. Temperature, T / K 400 500 600 700 800 Kp 3.00 × 1058 5.86 × 1045 1.83 × 1037 1.46 × 1031 1.14 × 1026 1 T / K−1 2.50 × 10−3 ...................... ...................... ...................... ...................... ln Kp 135 ...................... ...................... ...................... ...................... [2]
58. November 2020 · Paper 3 · Q5(c) · 4 marks · AO3
(c) Plot a graph of ln Kp against 1 T using the axes provided on the opposite page. Use your graph and equation 5.1 to determine ∆H, in kJ mol−1, for this equilibrium. Give your answer to 3 significant figures. ∆H = ........................................... kJ mol−1 [4]
59. November 2020 · Paper 3 · Q5(d) · 2 marks · AO3
(d) Explain how ∆S could be calculated from a graph of ln Kp against 1 T . ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [2]
60. June 2019 · Paper 1 · Q18(c)(i) · 1 marks · AO3
(c) Iron(II) gluconate, C12H22FeO14, is the active ingredient in some brands of iron supplements. A student carries out an experiment to determine the mass of iron(II) gluconate in one tablet of an iron supplement, using the method below. Stage 1 The student crushes two tablets and dissolves the powdered tablets in dilute sulfuric acid. Stage 2 The student makes up the solution from Stage 1 to 250.0 cm3 in a volumetric flask. Stage 3 The student then titrates 25.0 cm3 portions of the solution obtained in Stage 2 with 0.00200 mol dm−3 potassium manganate(VII). The student obtains a mean titre of 13.50 cm3. In this titration, 1 mol of manganate(VII) ions reacts with 5 mol of iron(II) ions. (i) Explain why the student used 0.00200 mol dm−3 potassium manganate(VII) solution for this titration, rather than the more usual concentration of 0.0200 mol dm−3 used in manganate(VII) titrations. ........................................................................................................................................... ...................................................................................................................................... [1]
61. June 2019 · AS Paper 1 · Q22(a)(i) · 1 marks · AO2
22 A student carries out a titration to determine the concentration of some hydrochloric acid. The student titrates the hydrochloric acid against a standard solution of sodium carbonate, Na2CO3. The equation is shown below. Na2CO3(aq) + 2HCl (aq) → 2NaCl (aq) + H2O(l) + CO2(g) • The student prepares 0.150 mol dm−3 Na2CO3 in a 250.0 cm3 volumetric flask. • The hydrochloric acid is added to a 50.0 cm3 burette. • The student pipettes the Na2CO3(aq) using a 25.0 cm3 pipette. (a) The student’s burette readings are shown in the table. The rough titre has been omitted. (i) Complete the table by adding the titres to the table. Final reading / cm3 24.60 48.45 34.30 Initial reading / cm3 0.40 24.60 10.00 Titre / cm3 ................... ................... ................... [1]
62. June 2019 · AS Paper 1 · Q22(c) · 2 marks · AO3
(c) In the titrations, the student measured volumes with a pipette and a burette. • The pipette had an uncertainty of ± 0.04 cm3 in the volume measured. • The burette had an uncertainty of ± 0.05 cm3 in the volume measured. Determine whether the volume measured by the pipette or the volume measured by the burette has the greater percentage uncertainty. [2]
63. June 2019 · AS Paper 2 · Q1(d)(ii) · 1 marks · AO3
(ii) Suggest why the student takes four readings of the mass of the crucible and residue. ........................................................................................................................................... ...................................................................................................................................... [1]
64. June 2019 · AS Paper 2 · Q1(d)(iii) · 2 marks · AO3
(iii) Suggest two modifications to the method that would reduce the percentage uncertainty in the mass of the residue. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... [2]
65. June 2019 · AS Paper 2 · Q2(a) · 6 marks · AO2
2 Magnesium nitrate is used in fertilisers as a source of nitrogen. (a)* A student plans to prepare 250.0 cm3 of a 0.4000 mol dm–3 solution of magnesium nitrate, starting from magnesium nitrate crystals, Mg(NO3)2•6H2O. Describe how the student would prepare the solution, giving full details of quantities, apparatus and method. [6] ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... Additional answer space if required ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...................................................................................................................................................
66. June 2019 · AS Paper 2 · Q4(b)(i) · 1 marks · AO2
(b) The student uses the apparatus in the diagram. 100 cm3 gas syringe The student’s method is outlined below: • Pour 50.0 cm3 of 0.100 mol dm–3 HCl into the conical flask. • Add 0.200 g of zinc (an excess), and quickly attach the delivery tube and gas syringe. • Measure the volume of gas collected every 20 seconds until the reaction stops. The student obtains the results shown in Table 4.1. Time / s 0 20 40 60 80 100 120 160 200 Volume of gas / cm3 0 16 27 37 39 50 53 58 58 Table 4.1 (i) On the graph paper in Fig. 4.1, label the x axis and plot the results in Table 4.1. [1]
67. June 2019 · AS Paper 2 · Q4(b)(ii) · 1 marks · AO2
(ii) Circle any anomalous results present in the graph you have drawn in Fig. 4.1. [1]
68. June 2019 · AS Paper 2 · Q4(b)(iii) · 1 marks · AO3
(iii) Draw a best-fit smooth curve on the graph you have drawn in Fig. 4.1. [1]
69. June 2019 · Paper 3 · Q3(a)(iii) · 2 marks · AO3
(iii) The student was not sure that all the oxygen had been removed from the lead oxide. Suggest two modifications that the student could make to their method to be confident that all the oxygen had been removed. Explain your reasoning. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... [2]
70. June 2019 · Paper 3 · Q5(a)(ii) · 1 marks · AO2
(ii) The thermometer had an uncertainty in each temperature reading of ± 0.1 °C. The student calculates a 20% uncertainty in the temperature change in Experiment 2. Calculate the temperature change in Experiment 2. temperature change = .................................................... °C [1]
71. June 2018 · AS Paper 1 · Q12 · 1 marks ·
12 A student carried out an experiment to measure the enthalpy change of combustion of methanol. The energy from the combustion of methanol was used to heat a beaker containing water. The student’s calculated enthalpy change of combustion was more exothermic than the value in data books. Which error could have caused this difference? A Some methanol had evaporated from the wick before the final weighing. B In the calculation, the student used the molar mass of ethanol instead of methanol. C There was incomplete combustion. D The water boiled for 5 minutes before the final temperature was taken. Your answer [1]
72. June 2018 · Paper 1 · Q17(b)(i) · 3 marks ·
(b) A student carries out an investigation to find the activation energy, Ea, and the pre-exponential factor, A, of a reaction. The student determines the rate constant, k, at different temperatures, T. The student then plots a graph of ln k against 1 / T as shown below. 33.00 32.00 31.00 30.00 In k 29.00 28.00 27.00 26.00 0.00 1.00 2.00 3.00 4.00 5.00 1 / T /10–3 K–1 (i) Draw a best-fit straight line and calculate the activation energy, in J mol–1. Give your answer to three significant figures. Show your working. activation energy, Ea = + ............................................. J mol–1 [3]
73. June 2018 · Paper 1 · Q20(d)(i) · 2 marks ·
(d) Compound B is an iodate(V) salt of a Group 1 metal. The iodate(V) ion has the formula IO3 –. A student carries out a titration to find the formula of compound B. Step 1: The student dissolves 1.55 g of B in water and makes up the solution to 250.0 cm3 in a volumetric flask. Step 2: The student pipettes 25.00 cm3 of the solution of B into a conical flask, followed by 10 cm3 of dilute sulfuric acid and an excess of KI(aq). The iodate(V) ions are reduced to iodine, as shown below. IO3 –(aq) + 6H+(aq) + 5I–(aq) 3I2(aq) + 3H2O(l) Step 3: The resulting mixture is titrated with 0.150 mol dm–3 Na2S2O3(aq). 2S2O3 2–(aq) + I2(aq) S4O6 2–(aq) + 2I–(aq) The student repeats step 2 and step 3 until concordant titres are obtained. Titration readings Titration Trial 1 2 3 Final burette reading / cm3 24.00 47.40 23.75 47.05 Initial burette reading / cm3 0.00 24.00 0.00 23.20 Titre / cm3 Table 20.1 (i) Complete Table 20.1 and calculate the mean titre that the student should use for analysing the results. mean titre = .................................................. cm3 [2]
74. June 2018 · Paper 1 · Q20(d)(ii) · 1 marks ·
(ii) The uncertainty in each burette reading is ±0.05 cm3. Calculate the percentage uncertainty in the titre obtained from titration 1. Give your answer to two decimal places. percentage uncertainty = ..................................................... % [1]
75. June 2018 · AS Paper 1 · Q22(a)(iii) · 2 marks ·
(iii) How could the student obtain a sample of magnesium phosphate after reacting magnesium with phosphoric acid? ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
76. June 2018 · AS Paper 2 · Q1(c)(i) · 4 marks ·
(c) The student carries out a trial, followed by three further titrations. The diagram shows the initial and final burette readings for the three further titrations. The student measures all burette readings to the nearest 0.05 cm3. Titration 1 Titration 2 Titration 3 Initial reading Final reading Initial reading Final reading Initial reading Final reading 0 27 0 27 0 27 1 28 1 28 1 28 2 29 2 29 2 29 (i) Record the student’s readings and the titres in the table below. Calculate the mean titre, to the nearest 0.05 cm3, that the student should use for analysing the results. Titration 1 Titration 2 Titration 3 Final reading/cm3 Initial reading/cm3 Titre/cm3 mean titre = .................................................. cm3 [4]
77. June 2018 · AS Paper 2 · Q1(c)(ii) · 1 marks ·
(ii) The uncertainty in each burette reading is ± 0.05 cm3. Calculate the percentage uncertainty for the titre in Titration 1. percentage uncertainty = ..................................................... % [1]
78. June 2018 · Paper 3 · Q2(a)(i) · 5 marks ·
2 This question looks at reactions of hydrogen peroxide and of cobalt(II) ions. (a) Aqueous hydrogen peroxide decomposes as shown in equation 2.1. 2H2O2(aq) → 2H2O(l) + O2(g) Equation 2.1 The reaction is catalysed by manganese(IV) oxide, MnO2. A student investigates the decomposition of a hydrogen peroxide solution as outlined below. • The student adds 50.00 cm3 of H2O2(aq) to a conical flask. • The student adds a small spatula measure of MnO2 and quickly connects the flask to a gas syringe. • The student measures the volume of oxygen every 200 seconds. Results Time/s Volume of O2/cm3 0 0 200 15 400 28 600 36 800 41 1000 46 1200 48 1400 50 (i) Process the results as outlined below. • On page 5, plot a graph of volume of O2 against time. • Use your graph to find the rate of the reaction, in cm3 s–1, at t = 500 s. Show your working on the graph and in the space below. rate = ..............................................cm3 s–1 [5]
79. June 2017 · AS Paper 1 · Q5 · 1 marks ·
5 The burette readings from a titration are shown below. Final reading / cm3 24.95 Initial reading / cm3 5.00 The burette used has an uncertainty of ±0.05 cm3 in each reading. What is the percentage uncertainty of the resulting titre? A 0.20% B 0.25% C 0.45% D 0.50% Your answer [1]
80. June 2017 · Paper 1 · Q19(a) · 3 marks ·
19 Aqueous solutions of hydrogen peroxide, H2O2(aq), decompose as in the equation below. 2H2O2(aq) 2H2O(l) + O2(g) A student investigates the decomposition of H2O2(aq) by measuring the volume of oxygen gas produced over time. All gas volumes are measured at room temperature and pressure. The student uses 25.0 cm3 of 2.30 mol dm–3 H2O2. From the results, the student determines the concentration of H2O2(aq) at each time. The student then plots a concentration–time graph. 2.5 2.0 1.5 [H2O2(aq)] / mol dm–3 1.0 0.5 0.0 0 500 1000 1500 2000 2500 3000 time / s (a) Determine the total volume of oxygen, measured at room temperature and pressure, that the student should be prepared to collect in this investigation. Suggest apparatus that would allow this gas volume to be collected, indicating clearly the scale of working. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [3]
81. June 2017 · AS Paper 1 · Q24(c)(ii) · 2 marks ·
(ii) Suggest one assumption that the student has made that might mean that their calculated concentration of ethanoic acid in the vinegar is invalid. Predict, with a reason, how the experimental result would differ from the actual concentration of CH3COOH if the assumption were not correct. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
82. June 2017 · AS Paper 2 · Q2 · 6 marks ·
2* A student was asked to carry out an experiment to determine the initial rate of reaction of zinc and hydrochloric acid. The student plans to collect a total of about 72 cm3 of hydrogen at RTP and to use an excess of zinc. The student selects the following apparatus: • the apparatus shown in the diagram • 100 cm3 measuring cylinder • stop clock • 2 decimal place balance 100 cm3 gas syringe Outline how the student could carry out the experiment and explain how the results could be processed graphically. Show all working in your calculations. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [6]
83. June 2017 · AS Paper 2 · Q3(a)(ii) · 2 marks ·
(ii) The calculated value of ∆cH for hexane from this experiment is different from the data book value. Suggest two reasons for this difference. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... [2]
84. June 2017 · AS Paper 2 · Q3(b)(i) · 1 marks ·
(b) Data book values for the standard enthalpy changes of combustion, ∆cH , of the first four alkanes are shown in the table. Alkane methane ethane propane butane ∆cH / kJ mol−1 –890 –1560 –2219 –2877 (i) The values for the first three alkanes are plotted on the graph below. Plot the value for butane on the graph. relative molecular mass 0 20 40 60 80 100 –1000 –2000 ΔcH / kJ mol–1 –3000 –4000 –5000 [1]
85. June 2017 · AS Paper 2 · Q3(b)(ii) · 3 marks ·
(ii) Use the graph to estimate the energy released during complete combustion of 1.80 g of pentane. Show relevant working below and on the graph. energy released = .................................................... kJ [3]
86. June 2017 · Paper 2 · Q17(b)(i) · 1 marks ·
(b) A student investigates the relative ease of nitration of phenol, benzene, and benzoic acid. OH COOH phenol benzene benzoic acid The student finds that the conditions required for the nitration of each compound are different, as shown in Table 17.1. Compound phenol benzene benzoic acid Dilute HNO3 Concentrated HNO3 Concentrated HNO3 Conditions required 20 °C 55 °C 100 °C for nitration No catalyst H2SO4 catalyst H2SO4 catalyst Table 17.1 (i) State the trend in the relative ease of nitration of phenol, benzene, and benzoic acid. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1]
87. June 2017 · Paper 3 · Q2(b) · 2 marks ·
(b) The uncertainty in each temperature reading is ±0.1 °C. The uncertainty in each mass reading is ±0.005 g. Determine whether the mass of Na2O or the temperature change has the greater percentage uncertainty. Show all your working. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2]
88. June 2017 · Paper 3 · Q2(c) · 2 marks ·
(c) Suggest a modification to this experiment, using the same apparatus, which would reduce the percentage errors in the measurements. Explain your reasoning. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2]
89. June 2017 · Paper 3 · Q4(a)(i) · 4 marks ·
4 This question is about weak acids. (a) Compound A is a weak monobasic acid. A student is supplied with a 250.0 cm3 solution prepared from 2.495 g of A. The student titrates 25.0 cm3 samples of this solution with 0.0840 mol dm−3 NaOH in the burette. The student carries out a trial, followed by the three further titrations. The diagrams show the initial burette readings and the final burette readings for the student’s three further titrations. All burette readings are measured to the nearest 0.05 cm3. Titration 1 Titration 2 Titration 3 Initial reading Final reading Initial reading Final reading Initial reading Final reading 0 23 23 45 9 32 1 24 24 46 10 33 2 25 25 47 11 34 (i) Record the student’s readings and the titres in an appropriate format. Calculate the mean titre that the student should use for analysing the results. mean titre = .................................................. cm3 [4]
90. June 2016 · AS Paper 1 · Q22(b)(i) · 1 marks · AO2
(b) A student carries out an experiment to determine the amount of water of crystallisation in the formula of another hydrated salt. The student intends to remove the water by heating the hydrated salt. A diagram of the apparatus used by the student is shown below. crucible pipeclay triangle • The student adds the hydrated salt to the crucible and weighs the crucible and contents. • The student heats the crucible and contents and allows them to cool. • The student weighs the crucible and residue. The student’s results are shown below. Mass of crucible + hydrated salt / g 16.84 Mass of crucible + residue after heating / g 16.26 15 (i) The maximum error in each mass measurement using the balance is ±0.005 g. Calculate the percentage error in the mass of water removed. percentage error = ......................................................% [1]
91. June 2016 · AS Paper 1 · Q22(b)(ii) · 1 marks · AO3
(ii) Suggest one modification that the student could make to their method to reduce the percentage error in the mass of water removed. ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [1]
92. June 2016 · AS Paper 1 · Q22(b)(iii) · 1 marks · AO3
(iii) The student is not sure that all the water of crystallisation has been removed. How could the student modify the experiment to be confident that all the water of crystallisation has been removed? ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [1]
93. June 2016 · AS Paper 2 · Q1(c)(i) · 2 marks · AO3
3 (c) A student reacts a Group 2 metal, M, with water. M(s) + 2H2O(l) M(OH)2(aq) + H2(g) The student measures the volume of hydrogen gas produced. 0.162 g of the metal produces 97.0 cm3 of gas measured at room temperature and pressure. (i) Draw a labelled diagram of the apparatus that can be used to carry out this experiment. [2]
94. June 2016 · AS Paper 2 · Q5(b)(ii) · 2 marks · AO3
(ii) Using the graph, calculate the rate of reaction, in g s–1, at 200 seconds. Show your working on the graph. rate of reaction = ................................................. g s–1 [2]
95. June 2016 · AS Paper 2 · Q5(c) · 3 marks · AO3
(c) Outline a method that could be used to obtain the results that are plotted on the graph. Your answer should include the apparatus required and the procedure for the experiment. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [3]
96. June 2016 · AS Paper 2 · Q6(c)(ii) · 2 marks · AO3
15 (ii) A student plans to carry out this oxidation using the apparatus shown in the diagram. Give one reason why the apparatus is not suitable and describe a more suitable way of carrying out this oxidation. ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]

Mark schemes

1. June 2025 · AS Paper 1 · Q1
Mark scheme June 2025 Paper 1 Q1
2. June 2025 · Paper 1 · Q8
Mark scheme June 2025 Paper 1 Q8
3. June 2025 · Paper 1 · Q18(c)(ii)
Mark scheme June 2025 Paper 1 Q18(c)(ii)
4. June 2025 · AS Paper 2 · Q2(b)(ii)
Mark scheme June 2025 Paper 2 Q2(b)(ii)
5. June 2025 · AS Paper 2 · Q2(b)(iii)
Mark scheme June 2025 Paper 2 Q2(b)(iii)
6. June 2025 · AS Paper 2 · Q3(b)
Mark scheme June 2025 Paper 2 Q3(b)
7. June 2025 · Paper 2 · Q19(b)(ii)
Mark scheme June 2025 Paper 2 Q19(b)(ii)
8. June 2025 · Paper 3 · Q3(a)
Mark scheme June 2025 Paper 3 Q3(a)
9. June 2024 · Paper 1 · Q19(b)(i)
Mark scheme June 2024 Paper 1 Q19(b)(i)
10. June 2024 · AS Paper 1 · Q22(b)(i)
Mark scheme June 2024 Paper 1 Q22(b)(i)
11. June 2024 · AS Paper 2 · Q3(b)
Mark scheme June 2024 Paper 2 Q3(b)
12. June 2024 · AS Paper 2 · Q4(b)(i)
Mark scheme June 2024 Paper 2 Q4(b)(i)
13. June 2024 · AS Paper 2 · Q4(c)
Mark scheme June 2024 Paper 2 Q4(c)
14. June 2024 · Paper 2 · Q23(b)(ii)
Mark scheme June 2024 Paper 2 Q23(b)(ii)
15. June 2024 · Paper 3 · Q3(b)(ii)
Mark scheme June 2024 Paper 3 Q3(b)(ii)
16. June 2024 · Paper 3 · Q3(b)(iii)
Mark scheme June 2024 Paper 3 Q3(b)(iii)
17. June 2023 · Paper 1 · Q18(c)(ii)
Mark scheme June 2023 Paper 1 Q18(c)(ii)
18. June 2023 · Paper 1 · Q21(a)(ii)
Mark scheme June 2023 Paper 1 Q21(a)(ii)
19. June 2023 · Paper 1 · Q21(b)
Mark scheme June 2023 Paper 1 Q21(b)
20. June 2023 · AS Paper 1 · Q22(c)(ii)
Mark scheme June 2023 Paper 1 Q22(c)(ii)
21. June 2023 · AS Paper 2 · Q1(b)(iii)
Mark scheme June 2023 Paper 2 Q1(b)(iii)
22. June 2023 · AS Paper 2 · Q2(b)(ii)
Mark scheme June 2023 Paper 2 Q2(b)(ii)
23. June 2023 · AS Paper 2 · Q2(b)(iii)
Mark scheme June 2023 Paper 2 Q2(b)(iii)
24. June 2023 · AS Paper 2 · Q4(b)(i)
Mark scheme June 2023 Paper 2 Q4(b)(i)
25. June 2023 · AS Paper 2 · Q4(b)(ii)
Mark scheme June 2023 Paper 2 Q4(b)(ii)
26. June 2023 · Paper 3 · Q4(b)(ii)
Mark scheme June 2023 Paper 3 Q4(b)(ii)
27. June 2022 · Paper 1 · Q17(a)(ii)
Mark scheme June 2022 Paper 1 Q17(a)(ii)
28. June 2022 · Paper 1 · Q19(a)(i)
Mark scheme June 2022 Paper 1 Q19(a)(i)
29. June 2022 · AS Paper 1 · Q24(b)
Mark scheme June 2022 Paper 1 Q24(b)
30. June 2022 · AS Paper 2 · Q1(c)
Mark scheme June 2022 Paper 2 Q1(c)
31. June 2022 · AS Paper 2 · Q3(a)(ii)
Mark scheme June 2022 Paper 2 Q3(a)(ii)
32. November 2021 · Paper 1 · Q18(e)(i)
Mark scheme November 2021 Paper 1 Q18(e)(i)
33. November 2021 · Paper 1 · Q18(e)(ii)
Mark scheme November 2021 Paper 1 Q18(e)(ii)
34. November 2021 · Paper 1 · Q18(f)
Mark scheme November 2021 Paper 1 Q18(f)
35. November 2021 · AS Paper 1 · Q23(d)
Mark scheme November 2021 Paper 1 Q23(d)
36. November 2021 · AS Paper 1 · Q25(a)(ii)
Mark scheme November 2021 Paper 1 Q25(a)(ii)
37. November 2021 · AS Paper 2 · Q3(b)(i)
Mark scheme November 2021 Paper 2 Q3(b)(i)
38. November 2021 · AS Paper 2 · Q3(b)(iii)
Mark scheme November 2021 Paper 2 Q3(b)(iii)
39. November 2021 · AS Paper 2 · Q3(b)(iv)
Mark scheme November 2021 Paper 2 Q3(b)(iv)
40. November 2021 · AS Paper 2 · Q3(d)
Mark scheme November 2021 Paper 2 Q3(d)
41. November 2021 · AS Paper 2 · Q6(a)
Mark scheme November 2021 Paper 2 Q6(a)
42. November 2021 · AS Paper 2 · Q6(b)
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43. November 2021 · Paper 3 · Q2(a)
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44. November 2021 · Paper 3 · Q2(b)
Mark scheme November 2021 Paper 3 Q2(b)
45. November 2021 · Paper 3 · Q2(c)
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46. November 2021 · Paper 3 · Q2(d)
Mark scheme November 2021 Paper 3 Q2(d)
47. November 2021 · Paper 3 · Q4(c)(ii)
Mark scheme November 2021 Paper 3 Q4(c)(ii)
48. November 2020 · Paper 1 · Q1
Mark scheme November 2020 Paper 1 Q1
49. November 2020 · Paper 1 · Q20(a)(i)
Mark scheme November 2020 Paper 1 Q20(a)(i)
50. November 2020 · AS Paper 1 · Q23(c)
Mark scheme November 2020 Paper 1 Q23(c)
51. November 2020 · AS Paper 2 · Q2(c)(i)
Mark scheme November 2020 Paper 2 Q2(c)(i)
52. November 2020 · AS Paper 2 · Q2(c)(ii)
Mark scheme November 2020 Paper 2 Q2(c)(ii)
53. November 2020 · AS Paper 2 · Q2(c)(iii)
Mark scheme November 2020 Paper 2 Q2(c)(iii)
54. November 2020 · Paper 3 · Q3(a)(ii)
Mark scheme November 2020 Paper 3 Q3(a)(ii)
55. November 2020 · Paper 3 · Q4(c)(i)
Mark scheme November 2020 Paper 3 Q4(c)(i)
56. November 2020 · Paper 3 · Q4(c)(ii)
Mark scheme November 2020 Paper 3 Q4(c)(ii)
57. November 2020 · Paper 3 · Q5(a)
Mark scheme November 2020 Paper 3 Q5(a)
58. November 2020 · Paper 3 · Q5(c)
Mark scheme November 2020 Paper 3 Q5(c)
59. November 2020 · Paper 3 · Q5(d)
Mark scheme November 2020 Paper 3 Q5(d)
60. June 2019 · Paper 1 · Q18(c)(i)
Mark scheme June 2019 Paper 1 Q18(c)(i)
61. June 2019 · AS Paper 1 · Q22(a)(i)
Mark scheme June 2019 Paper 1 Q22(a)(i)
62. June 2019 · AS Paper 1 · Q22(c)
Mark scheme June 2019 Paper 1 Q22(c)
63. June 2019 · AS Paper 2 · Q1(d)(ii)
Mark scheme June 2019 Paper 2 Q1(d)(ii)
64. June 2019 · AS Paper 2 · Q1(d)(iii)
Mark scheme June 2019 Paper 2 Q1(d)(iii)
65. June 2019 · AS Paper 2 · Q2(a)
Mark scheme June 2019 Paper 2 Q2(a)
66. June 2019 · AS Paper 2 · Q4(b)(i)
Mark scheme June 2019 Paper 2 Q4(b)(i)
67. June 2019 · AS Paper 2 · Q4(b)(ii)
Mark scheme June 2019 Paper 2 Q4(b)(ii)
68. June 2019 · AS Paper 2 · Q4(b)(iii)
Mark scheme June 2019 Paper 2 Q4(b)(iii)
69. June 2019 · Paper 3 · Q3(a)(iii)
Mark scheme June 2019 Paper 3 Q3(a)(iii)
70. June 2019 · Paper 3 · Q5(a)(ii)
Mark scheme June 2019 Paper 3 Q5(a)(ii)
71. June 2018 · AS Paper 1 · Q12
Mark scheme June 2018 Paper 1 Q12
72. June 2018 · Paper 1 · Q17(b)(i)
Mark scheme June 2018 Paper 1 Q17(b)(i)
73. June 2018 · Paper 1 · Q20(d)(i)
Mark scheme June 2018 Paper 1 Q20(d)(i)
74. June 2018 · Paper 1 · Q20(d)(ii)
Mark scheme June 2018 Paper 1 Q20(d)(ii)
75. June 2018 · AS Paper 1 · Q22(a)(iii)
Mark scheme June 2018 Paper 1 Q22(a)(iii)
76. June 2018 · AS Paper 2 · Q1(c)(i)
Mark scheme June 2018 Paper 2 Q1(c)(i)
77. June 2018 · AS Paper 2 · Q1(c)(ii)
Mark scheme June 2018 Paper 2 Q1(c)(ii)
78. June 2018 · Paper 3 · Q2(a)(i)
Mark scheme June 2018 Paper 3 Q2(a)(i)
79. June 2017 · AS Paper 1 · Q5
Mark scheme June 2017 Paper 1 Q5
80. June 2017 · Paper 1 · Q19(a)
Mark scheme June 2017 Paper 1 Q19(a)
81. June 2017 · AS Paper 1 · Q24(c)(ii)
Mark scheme June 2017 Paper 1 Q24(c)(ii)
82. June 2017 · AS Paper 2 · Q2
Mark scheme June 2017 Paper 2 Q2
83. June 2017 · AS Paper 2 · Q3(a)(ii)
Mark scheme June 2017 Paper 2 Q3(a)(ii)
84. June 2017 · AS Paper 2 · Q3(b)(i)
Mark scheme June 2017 Paper 2 Q3(b)(i)
85. June 2017 · AS Paper 2 · Q3(b)(ii)
Mark scheme June 2017 Paper 2 Q3(b)(ii)
86. June 2017 · Paper 2 · Q17(b)(i)
Mark scheme June 2017 Paper 2 Q17(b)(i)
87. June 2017 · Paper 3 · Q2(b)
Mark scheme June 2017 Paper 3 Q2(b)
88. June 2017 · Paper 3 · Q2(c)
Mark scheme June 2017 Paper 3 Q2(c)
89. June 2017 · Paper 3 · Q4(a)(i)
Mark scheme June 2017 Paper 3 Q4(a)(i)
90. June 2016 · AS Paper 1 · Q22(b)(i)
Mark scheme June 2016 Paper 1 Q22(b)(i)
91. June 2016 · AS Paper 1 · Q22(b)(ii)
Mark scheme June 2016 Paper 1 Q22(b)(ii)
92. June 2016 · AS Paper 1 · Q22(b)(iii)
Mark scheme June 2016 Paper 1 Q22(b)(iii)
93. June 2016 · AS Paper 2 · Q1(c)(i)
Mark scheme June 2016 Paper 2 Q1(c)(i)
94. June 2016 · AS Paper 2 · Q5(b)(ii)
Mark scheme June 2016 Paper 2 Q5(b)(ii)
95. June 2016 · AS Paper 2 · Q5(c)
Mark scheme June 2016 Paper 2 Q5(c)
96. June 2016 · AS Paper 2 · Q6(c)(ii)
Mark scheme June 2016 Paper 2 Q6(c)(ii)