Redox titrations: Edexcel International A Level Chemistry questions

Every Edexcel International A Level Chemistry exam question on Redox titrations (specification points 16.15–16.17), 2019–2025, with its mark scheme and examiner’s report.

All 64 questions on Redox titrations, as a list

June 2025, Unit 5, Q2(a) (1 mark): What colour change is seen at the end-point? (1) A pale pink to pale green B purple to pale pink C pale green to pale pink D pale pink to purple
June 2025, Unit 5, Q2(b) (1 mark): What is the concentration, in mol dm (1) −1 A 1.90 × 10 −3 B 7.58 × 10 −3 C 4.74 × 10 −4 D 1.90 × 10
June 2025, Unit 5, Q2(c) (1 mark): What is the percentage error in a single titre of 18.95 cm (1) 3] [The uncertainty in a single burette reading is ±0.05 cm A ± 0.20% B ± 0.26% C ± 0.40% D ± 0.5
June 2025, Unit 5, Q2(d) (1 mark): Which row shows the correct changes in oxidation states? (1) manganese iron II → VII III → II A II → VII II → III B VII → II III → II C VII → II II → III D Use
June 2025 (A), Unit 5, Q3(b) (1 mark): 25.0 cm3 of a 0.0200 mol dm–3 solution of ethanedioate ions is titrated with an acidified solution containing 0.0400 mol dm–3 manganate(VII) ions. What volume,
June 2025 (A), Unit 5, Q16(c)(ii) (2 marks): Calculate the moles of manganese(IV) oxide in the 50 cm3 sample. (2)
June 2025 (A), Unit 5, Q16(c)(iii) (4 marks): Calculate the concentration of dissolved oxygen, in ppm, in the sample collected. [Assume the density of water = 1.0 g cm–3] (4)
June 2025 (A), Unit 5, Q16(d)(iii) (2 marks): Deduce the effect, if any, on the value of dissolved oxygen obtained in (c)(iii) if the nitrate(III) ions are not removed prior to Step 2. No calculation is req
January 2025, Unit 5, Q21(b) (6 marks): Many moss killers contain iron(II) sulfate, FeSO4, as the active compound. Potassium manganate(VII) can be used to determine the amount of iron(II) sulfate pres
October 2024, Unit 5, Q16 (6 marks): Iron is generally prescribed when a person is suffering from anaemia. Many people find it easier to take medicine in liquid form rather than solid tablets. An i
October 2024, Unit 6, Q3(a)(iii) (1 mark): State why the titration needed no indicator. (1)
October 2024, Unit 6, Q3(a)(v) (4 marks): The mean titre was 19.90 cm3. Determine the value of x in (COOH)2.xH2O. (4)
June 2024, Unit 5, Q3(a) (1 mark): Which shows the changes in the oxidation states for iron and manganese? (1) Iron Manganese II → III VII → II A II → III VII → IV B III → II II → VII C III → II
June 2024, Unit 5, Q3(b) (1 mark): A 25.00 cm3 sample of FeSO4 dissolved in acid required 22.50 cm3 of 0.100 mol dm–3 KMnO4 for complete reaction. What is the concentration of the FeSO4 solution?
June 2024, Unit 6, Q3(a)(ii) (1 mark): State when the starch indicator should be added during the titrations in Step 5. (1)
January 2024, Unit 5, Q12(b) (1 mark): The titration was carried out with sodium thiosulfate in the burette and starch was added just before the end‑point. What would be the colour of the solution in
January 2024, Unit 5, Q16(b)(i) (1 mark): State the colour change at the end‑point of the titration. (1)
January 2024, Unit 5, Q16(b)(ii) (4 marks): Calculate the accurate concentration of the potassium manganate(VII), in mol dm–3, giving your answer to an appropriate number of significant figures. (4)
January 2024, Unit 5, Q16(b)(iii) (3 marks): A second titration carried out without the addition of sulfuric acid resulted in the formation of a brown suspension. Explain how the value of the mean titre wo
January 2024, Unit 6, Q3(c)(ii) (4 marks): Information about the experiment is shown. • 25.0 cm3 of 0.0200 mol dm–3 ammonium vanadate(V) was reduced by tin • 20.00 cm3 of 0.0100 mol dm–3 potassium mangan
January 2024, Unit 6, Q3(c)(iii) (2 marks): Explain the effect on the titre of leaving the tin in the reaction mixture. (2)
October 2023, Unit 5, Q18(c) (3 marks): When 25.0 cm3 of a 0.100 mol dm−3 solution of X2O5 reacts with a reducing agent, X is reduced to a lower oxidation state. To oxidise X back to its original oxid
October 2023, Unit 5, Q19(f) (5 marks): Potassium dichromate(VI) oxidises iron(II) ions to iron(III) ions in acid solution. 2− + 6Fe2+ + 14H+ → 2Cr3+ + 6Fe3+ + 7H2O Cr2O7 Iron(III) ions do not react w
June 2023, Unit 5, Q22 (6 marks): The amount of calcium ethanedioate, CaC2O4 , present in a sample of spinach is determined by redox titration. 11.4 g of spinach leaves are stirred in 50.0 cm3 o
January 2023, Unit 5, Q18(d)(i) (3 marks): Calculate the ratio of the number of moles of manganate(VII) ions, MnO4 to the number of moles of vanadium(III) ions, V3+, in this oxidation. You must show all
January 2023, Unit 5, Q18(d)(ii) (2 marks): Write the equation for the reaction between manganate(VII) ions and vanadium(III) ions in acidic solution. State symbols are not required. (2)
January 2023, Unit 6, Q3(a)(i) (1 mark): State what would happen in the titration if the mixture was not acidified. (1)
January 2023, Unit 6, Q3(a)(ii) (2 marks): Neither hydrochloric acid nor nitric acid can be used to acidify the titration mixture. For each acid give a reason why it cannot be used. (2)
January 2023, Unit 6, Q3(b) (4 marks): The ionic half‑equations for the reactions of the iron(II) ions and the manganate(VII) ions are shown. Fe2+ → Fe3+ + e– – + 8H+ + 5e– → Mn2+ + 4H2O MnO4 Calcula
January 2023, Unit 6, Q3(c) (3 marks): The titration is carried out using the apparatus shown. burette containing potassium manganate(VII) conical flask containing lawn sand and dilute sulfuric acid
October 2022, Unit 5, Q19(c)(i) (1 mark): Give the colour of the solution at the end‑point of the titration. (1)
October 2022, Unit 5, Q19(c)(ii) (2 marks): Suggest why the VO2+ ions formed do not affect the titration. (2)
October 2022, Unit 5, Q19(c)(iii) (7 marks): Calculate the percentage by mass of vanadium in the ferrovanadium. (7)
June 2022, Unit 5, Q15(a)(i) (1 mark): State the colour of each chromium species in the reaction. (1) 2− Cr2O7 Cr3+
June 2022, Unit 5, Q15(a)(ii) (1 mark): Suggest a reason why an indicator is needed in this titration. (1)
June 2022, Unit 5, Q15(a)(iii) (5 marks): Calculate the percentage by mass of potassium dichromate(VI) in the cement sample. (5)
June 2022, Unit 5, Q17(a)(i) (4 marks): Determine whether or not this type of brass is a gilding metal, by calculating its percentage by mass of copper. (4)
June 2022, Unit 6, Q3(c)(i) (1 mark): Give a possible reason why the starch indicator is added when the iodine colour is pale yellow rather than at the start of the titration. (1)
June 2022, Unit 6, Q3(c)(ii) (1 mark): Give the colour change at the end‑point of the reaction. (1)
June 2022, Unit 6, Q3(c)(iii) (1 mark): The results of the titration are shown. Titration number 1 2 3 Final burette reading / cm3 27.05 28.65 27.45 Initial burette reading / cm3 0.00 2.00 1.00 Titre
June 2022, Unit 6, Q3(c)(iv) (3 marks): The redox equation for the reaction between copper(II) ions and iodide ions is shown. 2Cu2+(aq) + 4I–(aq) → 2CuI(s) + I2(aq) The reaction of sodium thiosulfate
June 2022, Unit 6, Q3(c)(v) (2 marks): Nitric acid reacts with iodide ions to form iodine. In another experiment the nitric acid was not neutralised before the start of Stage 2. Explain the effect on
January 2022, Unit 5, Q8(a) (1 mark): What concentration of thiosulfate ions, in mol dm−3 , is required to give a titre of approximately 20 cm3 ? (1) A 0.010 B 0.020 C 0.040 D 0.080
January 2022, Unit 5, Q8(b) (1 mark): What is the most suitable volume of 0.1 mol dm−3 potassium iodide solution, in cm3 , to add to the 10.0 cm3 of chlorine solution? (1) A 7.6 B 8.0 C 8.4 D 10.0
January 2022, Unit 5, Q8(c) (1 mark): What is the colour change at the end‑point of the titration? (1) A colourless to pale yellow B pale yellow to colourless C colourless to blue‑black D blue‑black
January 2022, Unit 5, Q13(b)(ii) (6 marks): Calculate the final oxidation state of the cerium ion formed in the reaction. (6)
October 2021, Unit 5, Q20(c)(i) (1 mark): State the colour change that would be observed at the end‑point of the titration. (1) From to
October 2021, Unit 5, Q20(c)(ii) (5 marks): Use the results to determine the final oxidation state of nitrogen in the titration. You must show your working. [Mr value: Mg(NO3)2∙6H2O = 256.3] (5)
October 2021, Unit 5, Q20(c)(iii) (2 marks): Write the overall ionic equation for the titration reaction using your answer to (ii) and the relevant half‑equations from the list below. (2)  TiO2+ + 2H+ + e
October 2021, Unit 5, Q20(c)(v) (1 mark): Suggest why the contents of the conical flask are heated. (1)
October 2021, Unit 5, Q20(c)(vi) (6 marks): The student’s teacher said, 2+ ions are colourless in aqueous solution, the titration can “As TiCl3 is blue and TiO be carried out without an alizarin indicator
October 2021, Unit 6, Q1(d)(iii) (1 mark): State at what point in the titration the starch solution should be added. (1)
October 2021, Unit 6, Q1(d)(iv) (5 marks): Only Cu2+ ions in the solution react with the aqueous potassium iodide. 2Cu2+ + 4I– ® 2CuI + I2 The iodine reacts with sodium thiosulfate solution. 2– + I2 ® S4
June 2021, Unit 5, Q18(b)(i) (1 mark): State the colour change at the end-point of the titration. (1)
June 2021, Unit 5, Q18(b)(ii) (5 marks): One student used 1.53 g of the wire (weighed directly on the balance pan) and obtained a mean titre of 27.35 cm3. Using half-equations 3 and 5 from the table, c
June 2021, Unit 5, Q18(b)(iii) (3 marks): A second student carried out the same experiment but used distilled water to make up the solution in the volumetric flask. A brown suspension formed during the
June 2021, Unit 5, Q18(c)(i) (2 marks): Complete the table. (2)
June 2021, Unit 5, Q18(c)(ii) (2 marks): A third student obtained a value of 95.863% for the proportion of iron in the wire. State whether or not this student has given their answer to an appropriate n
January 2021, Unit 5, Q19(d) (6 marks): The rare mineral mitscherlichite has the chemical formula K2CuCl4⦁nH2O. 4.26 g of mitscherlichite was dissolved in distilled water and the solution made up to 2
January 2021, Unit 6, Q2(e) (5 marks): Describe how to carry out the titration in Step 3. You should identify suitable apparatus and any additional chemicals required. (5)
January 2021, Unit 6, Q2(f) (6 marks): In Method 2, 50.0 cm3 of potassium chlorate(V) was mixed with 150 cm3 of 0.0750 mol dm–3 of iron(II) sulfate. The iron (II) sulfate was in excess. The whole of
January 2021, Unit 6, Q2(g) (2 marks): + 3H2O(l) → Cl–(aq) + 6H+(aq) + 3SO2– 4 (aq) (g) Explain the change, if any, to the value calculated in (f) if the chloride ions were not removed before the rea
October 2020, Unit 5, Q19 (1 mark): In acidic conditions, manganate(VII) ions are reduced to manganese(II) ions, Mn2+. In neutral conditions, manganate(VII) ions are reduced to manganese(IV) oxide
October 2020, Unit 5, Q25(f) (5 marks): The Lanthanides The lanthanides form a series in the Periodic Table comprising the elements from lanthanum, La (Z = 57) to lutetium, Lu (Z = 71). They have impo

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