plumiOxidation numbers and Roman numerals: OCR A‑Level Chemistry A questions
OCR A-Level Chemistry A past-paper questions on 2.1.5.1 Oxidation numbers and Roman numerals, 2016–2025, with mark schemes and examiner’s reports where available.
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Q19(b)(ii)
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All 32 questions on Oxidation numbers and Roman numerals, as a list
- June 2025, Paper 1, Q19(b)(ii) (3 marks): When heated, aqueous HNO2 disproportionates. The equation is shown below. 3HNO2(aq) HNO3(aq) + 2NO(g) + H2O(l) • What is meant by disproportionation? • Use oxid
- June 2025, Paper 3, Q4(a)(i) (1 mark): What is the systematic name of a SO3 [1]
- June 2025, AS Paper 1, Q6 (1 mark): What is the oxidation number of S in Na2S2O3? A –4 B –2 C +2 D +4 Your answer [1]
- June 2024, Paper 1, Q16(b)(iii) (1 mark): Mn3O4 is a compound in which Mn has two different oxidation states. The two oxidation states are different from the Mn in MnO2. Suggest the two oxidation states
- June 2024, Paper 3, Q4(a)(iii) (1 mark): The systematic name of H3PO4 is phosphoric(V) acid. What is the systematic name of H3PO3? [1]
- June 2024, Paper 3, Q4(b)(ii) (3 marks): Aqueous silver nitrate, AgNO3, is reduced by PH3. The unbalanced equation is shown below. Balance the equation and use oxidation numbers to explain why this is
- June 2024, AS Paper 1, Q21(b)(i) (1 mark): What is the systematic name for Fe2O3? [1]
- June 2023, Paper 3, Q2(a)(i) (1 mark): The oxidation number of chlorine is different in the two rubidium salts, RbCl O3 and RbCl O4. What is the name of RbCl O4? [1]
- June 2023, AS Paper 1, Q5 (1 mark): Which substance has the lowest oxidation number for sulfur? A Na2SO4 B S8 C SF2 D SO2 Your answer [1]
- June 2023, AS Paper 2, Q1(b)(i) (1 mark): The common name for TiO2 is titanium dioxide. What is the systematic name of TiO2? [1]
- June 2022, Paper 3, Q1(a)(ii) (1 mark): Two students discuss the oxidation numbers in ammonium nitrate, NH4NO3. One student claims that the two nitrogen atoms have the same oxidation number. The other
- June 2022, Paper 3, Q2(a)(ii) (3 marks): Calcium hypochlorite, Ca(Cl O)2, is heated. The Ca(Cl O)2 decomposes to form CaCl 2 and Ca(Cl O3)2. This is a disproportionation reaction. Write an equation for
- June 2022, AS Paper 1, Q23(b) (2 marks): ‘Oxyanions’ are ions containing oxygen combined with atoms of other elements. Roman numerals are used to show the oxidation state of the element in the oxyanion
- November 2021, Paper 1, Q2 (1 mark): A chlorate(VII) ion has a 1– charge. What is the formula for sodium chlorate(VII)? A NaCl O3 B NaCl O4 C NaCl O7 D NaCl O8 Your answer [1]
- November 2021, Paper 1, Q19(b)(i) (2 marks): Explain, in terms of oxidation numbers, why disproportionation has taken place. [2]
- November 2021, AS Paper 1, Q23(b) (2 marks): Chlorine can be prepared by reacting concentrated hydrochloric acid with manganese(IV) oxide, MnO2. 4HCl (aq) + MnO2(s) → Cl 2(g) + MnCl 2(aq) + 2H2O(l) Using o
- November 2020, Paper 1, Q18(a) (3 marks): A student adds magnesium metal to an aqueous solution of ethanoic acid, CH3COOH. A redox reaction takes place. Write the overall equation for this reaction and
- November 2020, Paper 1, Q22(b)(ii) (1 mark): Determine the oxidation number of nickel in compound J. oxidation number: [1]
- November 2020, AS Paper 1, Q7 (1 mark): Potassium ferrate(VI) contains two potassium ions for every ferrate(VI) ion. What is the formula of the ferrate(VI) ion? 2− A FeO3 2− B FeO4 2− C FeO5 2− D FeO6
- November 2020, AS Paper 2, Q3(d)(i) (1 mark): Write the systematic name for NaBrO3. [1]
- June 2019, Paper 1, Q5 (1 mark): What is the oxidation number of N in Mg(NO2)2•3H2O? A +2 B +3 C +4 D +5 Your answer [1]
- June 2019, AS Paper 2, Q2(c) (2 marks): Magnesium nitrate decomposes when heated, as shown in the equation. 2Mg(NO3)2(s) 2MgO(s) + 4NO2(g) + O2(g) Using oxidation numbers, show which element has been
- June 2018, Paper 1, Q2 (1 mark): In the compound [ICl2]+ [SbCl6]–, the oxidation number of chlorine is –1. 2 What are the oxidation numbers of I and Sb in the compound? I Sb A +1 +5 B +1 +7 C +
- June 2018, Paper 3, Q1(a)(vii) (1 mark): An element which forms a compound with hydrogen in which the element has an oxidation number of –4. [1]
- June 2018, Paper 3, Q4(a)(i) (1 mark): What is the oxidation number of platinum in cis-platin? [1]
- June 2018, AS Paper 1, Q6 (1 mark): What is the oxidation number of Fe in K2FeO4? A +4 B +5 C +6 D +7 Your answer [1]
- June 2017, Paper 1, Q3 (1 mark): What is the oxidation number of Mn in K2MnO4? A +4 B +5 C +6 D +7 Your answer [1]
- June 2017, Paper 1, Q17(c)(i) (3 marks): State what is meant by disproportionation and use oxidation numbers to show that disproportionation has taken place. [3]
- June 2017, Paper 1, Q17(c)(ii) (1 mark): What is the systematic name for KCl O4? [1]
- June 2017, Paper 3, Q2(d)(i) (1 mark): What is the systematic name for NaNO2? [1]
- June 2017, Paper 3, Q2(d)(ii) (2 marks): Using oxidation numbers, with signs, show the element that is oxidised and the element that is reduced in this reaction. Element oxidised Oxidation number chang
- June 2016, AS Paper 1, Q5 (1 mark): What is the oxidation number of nitrogen in Mg(NO3)2? A –3 B +2 C +5 D +6 Your answer [1]
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