Redox: OCR A‑Level Chemistry B questions

Every OCR A-Level Chemistry B exam question on ES Redox (specification points ES(b)–(g)), 2016–2025, with its mark scheme and examiner’s report.

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2,049 questions

Q35(a)(i)
June 2025 · Paper 1
1 markES Redox
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Q14
June 2025 · AS Paper 1
1 markES Redox
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Q24(a)(i)
June 2025 · AS Paper 1
4 marksES Redox
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Q24(a)(ii)
June 2025 · AS Paper 1
2 marksES Redox
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Q24(a)(iii)
June 2025 · AS Paper 1
1 markES Redox
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Q24(d)(i)
June 2025 · AS Paper 1
1 markES Redox
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Q24(d)(ii)
June 2025 · AS Paper 1
2 marksES Redox
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Q24
June 2024 · Paper 1
1 markES Redox
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Q5(c)
June 2024 · Paper 2
2 marksES Redox
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Q19
June 2024 · AS Paper 1
1 markES Redox
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Q20
June 2024 · AS Paper 1
1 markES Redox
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Q21(a)
June 2024 · AS Paper 1
1 markES Redox
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Q24(c)(i)
June 2024 · AS Paper 1
2 marksES Redox
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Q24(c)(ii)
June 2024 · AS Paper 1
1 markES Redox
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Q1(a)(ii)
June 2023 · Paper 2
2 marksES Redox
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Q1(d)
June 2023 · Paper 2
2 marksES Redox
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Q3(b)(i)
June 2023 · Paper 2
2 marksES Redox
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Q3(b)(ii)
June 2023 · Paper 2
3 marksES Redox
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Q11
June 2023 · AS Paper 1
1 markES Redox
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Q2(b)(ii)
June 2023 · AS Paper 2
1 markES Redox
The whole paper ↗

All 105 questions on Redox, as a list

June 2025, Paper 1, Q35(a)(i) (1 mark): Give the systematic name of the BrO3 [1]
June 2025, AS Paper 1, Q14 (1 mark): In which row does the compound have the correct systematic name? Compound Systematic name A Cu2O Copper(II) oxide B NaCl O Sodium hypochlorite C FeSO4 Iron(II)
June 2025, AS Paper 1, Q24(a)(i) (4 marks): Draw a labelled diagram of an apparatus they could use. [4]
June 2025, AS Paper 1, Q24(a)(ii) (2 marks): Write the half-equation for the reaction occurring at the cathode (negative electrode). [2]
June 2025, AS Paper 1, Q24(a)(iii) (1 mark): Name the substance formed at the anode. [1]
June 2025, AS Paper 1, Q24(d)(i) (1 mark): Give the systematic name for the IO3 [1]
June 2025, AS Paper 1, Q24(d)(ii) (2 marks): Identify the reducing agent in Equation 24.1. Explain your answer in terms of the change in oxidation state of the reducing agent. Reducing agent is: Oxidation
June 2024, Paper 1, Q24 (1 mark): 50 cm3 of 0.30 mol dm–3 Fe(II) in acid solution exactly reduces 25 cm3 of 0.10 mol dm–3 NaCl O3 solution. Fe(III) is formed. What is the oxidation state of chlo
June 2024, Paper 2, Q5(c) (2 marks): Give the oxidation states of oxygen in OH and O2 OH – O2 [2] Question 5(d) begins on page 18
June 2024, AS Paper 1, Q19 (1 mark): The reaction shown is sometimes used during the manufacture of bromine from sea water. Br2(aq) + SO2(g) + 2HBr(aq) + H2SO4(aq) What is correct about this reacti
June 2024, AS Paper 1, Q20 (1 mark): An aqueous solution of calcium nitrate is electrolysed. What is the product at the anode? A calcium B hydrogen C nitrogen D oxygen Your answer [1]
June 2024, AS Paper 1, Q21(a) (1 mark): Give the systematic name of NaHCO3. [1]
June 2024, AS Paper 1, Q24(c)(i) (2 marks): Assign oxidation states to the sulfur atoms in the equation. Write the oxidation states on the dotted lines below the atoms. 2–(aq) + 2H+(aq) S2O3 H2O(l) + SO2(
June 2024, AS Paper 1, Q24(c)(ii) (1 mark): State what is being oxidised and what is being reduced in the reaction. [1]
June 2023, Paper 2, Q1(a)(ii) (2 marks): Air is blown through the mixture to remove the bromine as a vapour. Sulfur dioxide is then added, and the mixture is dissolved in water. Bromine reacts to form
June 2023, Paper 2, Q1(d) (2 marks): The students titrate 25.0 cm3 of a solution of bromine with sodium thiosulfate in the presence of excess iodide ions. Br2 + 2I– 2Br– + I2 2– 2– + 2I– I2 + 2S2O3
June 2023, Paper 2, Q3(b)(i) (2 marks): The equation for the reaction at the cathode is shown. 2H+ + 2e– H2 Complete and balance the equation for the reaction at the anode: 4e– + + H2O [2]
June 2023, Paper 2, Q3(b)(ii) (3 marks): A mole of electrons is 96 500 coulombs. A coulomb is 1 amp flowing for 1 second. How long (in hours) would it take for a current of 100.0 amps to produce 20.0 g
June 2023, AS Paper 1, Q11 (1 mark): Chlorine is made by electrolysing sea water. The following reaction occurs at the anode. 2Cl –(aq) Cl 2(g) + 2e– Which statement is correct? A Chloride ions are
June 2023, AS Paper 2, Q2(b)(ii) (1 mark): Identify the oxidising agent and reducing agent in Equation 2.1. Oxidising agent Reducing agent [1]
June 2023, AS Paper 2, Q2(d)(i) (1 mark): Write a half-equation for the reaction that occurs in the presence of light. [1]
June 2023, AS Paper 2, Q2(d)(ii) (1 mark): Explain, in terms of electrons, whether silver ions are oxidised or reduced in this reaction. [1]
June 2023, AS Paper 2, Q2(e) (1 mark): The remaining silver bromide is removed by a developer, such as hydroquinone, C6H4(OH)2. This reacts with silver ions as shown: Ag+ + C6H4(OH)2 Ag + C6H4O2 + H+
June 2022, Paper 1, Q5 (1 mark): In which of the following reactions is iodine oxidised? A 2Na + I2 2NaI I2 + 2e– 2I– B I2 + 2At– At2 + 2I– C D I2 + F2 2IF Your answer [1]
June 2022, Paper 1, Q27 (1 mark): Iodine is formed from iodide ions by reaction with copper(II) ions as shown in the following ionic equation. 2Cu2+ + 4I– I2 + 2CuI The iodine formed can be titr
June 2022, Paper 1, Q31(c) (1 mark): Bromine can also be produced by the electrolysis of aqueous sodium bromide. Write the ionic half-equation for the production of bromine at the anode. [1]
June 2022, Paper 2, Q1(a) (1 mark): Give the systematic name for Fe2O3. [1]
June 2022, Paper 2, Q1(f) (10 marks): to form iodine. The iodine can then be titrated with sodium thiosulfate. Describe a method to measure the volume of sodium thiosulfate solution required to reac
June 2022, AS Paper 1, Q23(a) (1 mark): Give the systematic name for NaOCl. [1]
June 2022, AS Paper 1, Q23(b)(i) (1 mark): Give the half-equation for the reaction at the positive electrode when NaCl(aq) is electrolysed. [1]
June 2022, AS Paper 1, Q23(b)(ii) (1 mark): Give the half-equation for the production of hydroxide ions (and a gas) at the negative electrode when NaCl(aq) is electrolysed. [1]
June 2022, AS Paper 1, Q23(b)(iii) (1 mark): Suggest the equation for the two electrode products reacting to give OCl – ions. [1]
June 2022, AS Paper 1, Q23(c)(i) (2 marks): State which atoms are being oxidised in equation 23.2 and give their change in oxidation state. is being oxidised from to [2]
June 2022, AS Paper 1, Q23(c)(ii) (3 marks): A group of students measure out 25 cm3 of a bleach solution in a measuring cylinder and pour it into a conical flask. The students add excess hydrochloric acid
June 2022, AS Paper 1, Q23(c)(iii) (4 marks): The students find that 25 cm3 of the bleach solution needs 20.3 cm3 of 1.60 mol dm–3 sodium thiosulfate. Calculate the concentration of NaOCl in the bleach solu
November 2021, Paper 1, Q31(b)(i) (2 marks): Give the oxidation state of nitrogen in ammonium ions and nitrate ions. + Oxidation state of nitrogen in ammonium ions, NH4 – Oxidation state of nitrogen in nit
November 2021, Paper 2, Q2(a)(ii) (2 marks): Use oxidation states to state and explain what is being reduced in half-equation 3 in Table 2.1. [2]
November 2021, Paper 2, Q5(f) (2 marks): An aluminosilicate ion has the formula Al 2Si14O32 State and explain the value of x using oxidation states. [2]
November 2021, Paper 3, Q3(b)(i) (4 marks): Analysis of 25.0 cm3 of a sample of brine by this method gave an average titre of 14.20 cm3 of 1.00 × 10–3 mol dm–3 aqueous S2O3 2–. Calculate the concentration
November 2021, Paper 3, Q3(b)(ii) (2 marks): The reaction in Equation 3.2 is a redox reaction. 2–(aq) 2I–(aq) + S4O6 2–(aq) I2(aq) + 2S2O3 Equation 3.2 2–, is oxidised by the iodine. The thiosulfate ion, S
November 2021, AS Paper 1, Q5 (1 mark): What is the formula of chromium(III) oxide? A Cr3O B Cr3O2 C Cr2O3 D CrO3 Your answer [1]
November 2021, AS Paper 1, Q8 (1 mark): The overall equation for the electrolysis of aqueous chlorides to make chlorine is given below. 2Cl –(aq) + 2H2O(l) Cl 2(g) + 2OH–(aq) + H2(g) Which statement i
November 2021, AS Paper 1, Q15 (1 mark): Which row matches the correct systematic name and formula? Formula Systematic Name A CuO copper(I) oxide B HNO2 nitric(V) acid C PbO2 lead(IV) oxide D NaCl O so
November 2021, AS Paper 2, Q2(e)(i) (1 mark): Write the ionic half-equation for the oxidation reaction. [1]
November 2020, Paper 1, Q32(e)(i) (2 marks): Complete the oxidation states of Br and S in the table. HBr H2SO4 Br2 SO2 Oxidation state of Br Oxidation state of S [2]
November 2020, Paper 2, Q2(b)(i) (1 mark): Identify the oxidising agent in equation 2.1. [1]
November 2020, Paper 2, Q5(a)(i) (1 mark): Explain why the oxidation state of the platinum in cisplatin is +2. [1]
November 2020, AS Paper 1, Q3 (1 mark): Which is the correct systematic name that matches the formula? Formula Systematic name A Cu(OH)2 copper hydroxide B Fe2(SO4)3 iron(III) sulfate(VI) C Pb(NO3)2 l
November 2020, AS Paper 1, Q23(a) (1 mark): Suggest why it is necessary to separate the products in the cell. [1]
November 2020, AS Paper 1, Q23(b)(i) (1 mark): What is reduced in equation 23.1? Explain your answer. [1]
November 2020, AS Paper 1, Q23(b)(ii) (1 mark): Write the half-equation for the production of chlorine gas in the cell. [1]
June 2019, Paper 1, Q9 (1 mark): Which row of the table is correct? Formula Systematic name A NaCl O sodium chlorate(I) B CuS copper(I) sulfide C NaIO3 sodium iodate(III) D HNO2 nitrous acid Yo
June 2019, Paper 1, Q27 (1 mark): A reaction that occurs during the production of bromine in some industrial plants is shown below. Br2(aq) + SO2(g) + 2H2O(l) 2HBr(aq) + H2SO4(aq) Which statemen
June 2019, Paper 1, Q34(e)(i) (1 mark): Name a suitable indicator the students should use and give the expected colour change observed. Indicator Colour change observed [1]
June 2019, Paper 1, Q34(e)(ii) (3 marks): The students are supplied with 0.020 mol dm–3 sodium thiosulfate. The students add excess potassium iodide to 50 cm3 of the seawater and titrate with the sodium
June 2019, Paper 1, Q34(e)(iii) (1 mark): Calculate the percentage uncertainty in a titre of 0.95 cm3. percentage uncertainty = % [1]
June 2019, Paper 1, Q34(e)(iv) (2 marks): What could the students do to reduce this percentage uncertainty to around 0.5%? Describe their experimental method. [2]
June 2019, Paper 2, Q3(a) (2 marks): When chlorine reacts with hot hydroxide ions, part of the chlorine is oxidised to chlorate(V) and the rest of the chlorine is reduced to chloride. Use oxidation
June 2019, Paper 2, Q3(d)(ii) (1 mark): Name the reducing agent in your reaction in (d)(i). [1]
June 2019, AS Paper 1, Q8 (1 mark): What is formed at the cathode when aqueous aluminium sulfate is electrolysed? A Hydrogen B Oxygen C Aluminium D Sulfur dioxide Your answer [1]
June 2019, AS Paper 1, Q20 (1 mark): Which of the following is a redox reaction? A 2Na + 2H2O 2NaOH + H2 2– + 2H+ 2– + H2O B 2CrO4 Cr2O7 C CaCO3 + 2HCl CaCl2 + H2O D MgCO3 MgO + CO2 Your answer [1]
June 2019, AS Paper 2, Q2(a) (2 marks): A student investigates the electrolysis of aqueous sodium chloride in the laboratory using the apparatus shown below. small tubes sodium chloride solution graph
June 2019, AS Paper 2, Q2(b)(i) (1 mark): Explain what is meant by the (I) in chloric(I) acid. [1]
June 2019, AS Paper 2, Q2(c)(i) (4 marks): Chlorine is also used to sterilise swimming pool water. An analytical chemist uses a titration to find out the amount of chlorine in a sample of swimming pool w
June 2019, AS Paper 2, Q2(c)(ii) (3 marks): A student is asked to write a detailed plan for the titration carried out by the chemist. The student writes: Use a measuring cylinder to transfer 25 cm3 of swi
June 2019, AS Paper 2, Q2(d) (1 mark): Bromine can be extracted from seawater. One method of making bromine involves reacting chlorine gas with acidified seawater that contains bromide ions. Cl2(aq)
June 2018, Paper 1, Q8 (1 mark): Which formula has the correct systematic name? Formula Systematic name A Na2SO3 sodium sulfate(VI) B NaClO3 sodium chlorate(III) C Cu2S copper(I) sulfide D Pb(N
June 2018, Paper 1, Q27 (1 mark): Which row correctly shows the main products in electrolysis using graphite electrodes? Product at the Product at the Electrolyte anode cathode A MgBr2(l) bromin
June 2018, Paper 1, Q36(f)(i) (1 mark): Use oxidation states or some other method to balance equation 36.4. [1]
June 2018, Paper 2, Q3(b) (1 mark): Suggest the type of reaction by which hydrogen peroxide bleaches melanin. [1]
June 2018, Paper 2, Q5(d)(i) (3 marks): Draw a labelled diagram of a suitable apparatus, showing the reactants and products. [3]
June 2018, Paper 2, Q5(d)(ii) (2 marks): Write equations for the formation and decomposition of arsine in the apparatus. [2]
June 2018, Paper 3, Q2(a)(ii) (1 mark): Give the oxidation state of mercury in Hg2Cl2. oxidation state = [1]
June 2018, Paper 3, Q3(b)(i) (1 mark): The hydrogen peroxide oxidises the iodide ions in the fish to iodine. Write a half equation for this oxidation reaction. Explain why this reaction is classified
June 2018, Paper 3, Q3(b)(ii) (2 marks): The equation for the titration reaction is given below. 2−(aq) → 2I−(aq) + S4O6 2−(aq) I2(aq) + 2S2O3 Name the element oxidised in this reaction. Give its oxida
June 2018, Paper 3, Q3(b)(iii) (4 marks): The students obtained an average titre of 5.30 cm3 of 0.0010 mol dm−3 sodium thiosulfate. Calculate the mass of iodine in µg in a 120 g portion of fish. Give yo
June 2018, Paper 3, Q3(b)(iv) (1 mark): One of the students suggests that the titre value is too small and will lead to an unacceptably high percentage error. Calculate the percentage error based on t
June 2018, Paper 3, Q3(b)(v) (1 mark): Suggest how the experiment could be modified to improve the accuracy of the result. [1]
June 2018, AS Paper 2, Q4(a) (1 mark): Complete the table below to show the oxidation states for manganese and iodine in the reaction shown in equation 4.1. Element Initial oxidation state Final oxid
June 2018, AS Paper 2, Q4(b) (1 mark): The half-equation for the conversion of MnO2 to Mn2+ ions is shown below. MnO2 + 4H+ + 2e– Mn2+ + 2H2O Equation 4.2 Explain, in terms of electrons, why the mang
June 2018, AS Paper 2, Q4(e) (3 marks): The student collected 0.92 g of impure iodine, I2, and decided to determine its purity. The student dissolved the impure iodine in potassium iodide solution. Th
June 2017, Paper 1, Q7 (1 mark): Which process is not oxidation? + – A NH4 NO2 – B NO3 N2 C N2 NO – – D NO2 NO3 Your answer [1]
June 2017, Paper 1, Q31(a) (2 marks): Give the half equation for the reaction at the negative electrode during electrolysis and explain why it is reduction. Half-equation Explanation [2]
June 2017, Paper 1, Q31(f) (3 marks): The reaction in (e) is repeated with potassium iodide. The hydrogen iodide formed is oxidised to iodine and the sulfuric acid is reduced to hydrogen sulfide. Gi
June 2017, Paper 2, Q4(a)(i) (4 marks): Complete the table below showing the oxidation states of chromium species in the equations above. For each equation state whether chromium has been reduced, oxi
June 2017, Paper 2, Q4(b)(ii) (3 marks): Draw a labelled diagram of a simple apparatus to carry out chromium plating of a steel object in a student laboratory. [3]
June 2017, Paper 2, Q4(b)(iii) (1 mark): Write a half-equation for the cathode reaction in the cell in (b)(ii). [1]
June 2017, Paper 2, Q4(b)(iv) (3 marks): A ‘mole of electrons’ is 96 500 coulombs and a coulomb is a current of 1 amp flowing for 1 second. Calculate the time (in hours) needed to deposit 26 g of chrom
June 2017, Paper 3, Q4 (15 marks): (a) (i) Name the piece of apparatus which is most suitable for removing the 25.0 cm3 of the 4 Cu2+ ion solution. [1] (ii) Use the student’s results in the Pract
June 2017, AS Paper 2, Q3(b) (1 mark): Molten sodium chloride is electrolysed instead of an aqueous solution. What would be the similarity and the difference in the products at the two electrodes? Si
June 2017, AS Paper 2, Q3(c)(i): at the anode (positive electrode)
June 2017, AS Paper 2, Q3(c)(ii) (1 mark): at the cathode (negative electrode) [1]
June 2017, AS Paper 2, Q3(d)(i) (1 mark): at the anode (+) [1]
June 2017, AS Paper 2, Q3(d)(ii) (1 mark): at the cathode (–) [1]
June 2017, AS Paper 2, Q3(f)(i) (1 mark): Write the ionic half-equation for the oxidation reaction. [1]
June 2017, AS Paper 2, Q3(f)(ii) (1 mark): Identify the oxidising agent in the reaction in equation 3.1. [1]
June 2016, AS Paper 1, Q10 (1 mark): Tin reacts with concentrated nitric acid, as shown in the equation below. Sn + 4HNO3 4NO2 + SnO2 + 2H2O Which row represents the oxidation state changes for nit
June 2016, AS Paper 1, Q23(b)(i) (2 marks): Some ions in the solution can move through the membrane but others cannot. List these ions below. Can move through the membrane Cannot move through the membrane
June 2016, AS Paper 1, Q23(b)(ii) (1 mark): All three products from the membrane cell are used in the chemical industry. Write the overall equation for the formation of these three products in the cell. [
June 2016, AS Paper 1, Q23(c)(i) (1 mark): Write the oxidation states of bromine on the dotted lines beneath the equation. 5Br− + 6H+ + BrO3 − 3Br2 + 3H2O [1]
June 2016, AS Paper 1, Q23(c)(ii) (1 mark): State, with a reason, what has been reduced in the equation above. [1]
June 2016, AS Paper 2, Q2(c)(i) (1 mark): Explain the significance of the (VI) in the systematic name, sulfuric(VI) acid. [1]
June 2016, AS Paper 2, Q2(e)(i) (1 mark): Write a half-equation to represent the oxidation that is occurring in this reaction. [1]
June 2016, AS Paper 2, Q2(e)(ii) (1 mark): Explain why the half-equation in (e)(i) represents oxidation. [1]
June 2016, AS Paper 2, Q2(e)(iii) (1 mark): Identify the oxidising agent in the reaction in equation 2.1. [1]

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