plumiEmpirical and molecular formulae: OCR A‑Level Chemistry A questions
OCR A-Level Chemistry A past-paper questions on 2.1.3.2 Empirical and molecular formulae, 2016–2025, with mark schemes and examiner’s reports where available.
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Q21(b)(ii)
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All 38 questions on Empirical and molecular formulae, as a list
- June 2025, Paper 1, Q21(b)(ii) (4 marks): An iron(II) complex contains two different ligands: C5H5N, and Cl –. The complex has a molar mass of 442.8 g mol–1 and the following percentage composition by m
- June 2025, Paper 3, Q4(b)(i) (1 mark): What is the empirical formula of complex A? [1]
- June 2024, AS Paper 1, Q3 (1 mark): A nitrogen oxide contains 36.84% of nitrogen by mass. What is the empirical formula of the nitrogen oxide? A NO B NO2 C N2O D N2O3 Your answer [1]
- June 2023, Paper 1, Q2 (1 mark): 0.688 g of an oxide of manganese is reduced by hydrogen gas to form manganese metal and 0.235 g of water. What is the formula of the oxide of manganese? A MnO B
- June 2023, Paper 1, Q19(b) (5 marks): N2O4 reacts fully with oxygen to form a different oxide of nitrogen, oxide A, as the only product. Oxide A is collected and cooled to 75.0 °C at a pressure of 1
- June 2023, Paper 2, Q16(b)(iii) (3 marks): Organic compound B is formed by the substitution of some of the 14 H atoms in 2-methylpentane by Br atoms. 0.8649 g of compound B is heated until it is vaporise
- June 2023, AS Paper 1, Q2 (1 mark): A hydrocarbon contains 85.71% carbon by mass. What is the empirical formula of the hydrocarbon? A CH B CH2 C CH4 D C2H4 Your answer [1]
- June 2022, Paper 2, Q7 (1 mark): Complete combustion of 0.050 mol of an alkane produces 5.40 g of H2O. What is the molecular formula of the alkane? A C2H6 B C3H8 C C4H10 D C5H12 Your answer [1]
- June 2022, Paper 2, Q17 (6 marks): This question is about an analysis of an unknown organic Compound X. Some properties of Compound X are shown in the table. Molecular formula Functional groups C
- June 2022, Paper 2, Q18(b) (4 marks): A student is provided with two unknown carbonyl compounds, F and G. The compounds are analysed and found to have identical percentage compositions by mass: C: 6
- June 2022, AS Paper 1, Q26(b) (5 marks): A bromoalkane D is a liquid at room temperature and pressure but can easily be vaporised. When vaporised, 0.330 g of D produces 74.0 cm3 of gas at 1.01 × 105 Pa
- November 2021, Paper 3, Q1(d) (4 marks): Compound A has the following percentage composition by mass: Ca, 81.10%; N, 18.90%. A student reacts compound A with water to form alkaline gas B and alkali C.
- November 2021, AS Paper 1, Q4 (1 mark): Which alkane is 82.8% carbon by mass? A CH4 B C2H6 C C4H10 D C8H18 Your answer [1]
- November 2021, AS Paper 1, Q25(a)(i) (2 marks): Determine the empirical formula of the scandium oxide. empirical formula = [2]
- November 2021, AS Paper 1, Q25(a)(ii) (1 mark): 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 s
- November 2020, Paper 1, Q21(c) (3 marks): Compound A contains bromine and fluorine only, and has a boiling point of 41 °C. 1.26 g of compound A is heated to 80 °C. The volume of gas produced is 0.209 dm
- November 2020, Paper 1, Q22(b)(i) (3 marks): Calculate the values of x and y in the formula of compound J. x = y = [3]
- November 2020, Paper 2, Q11 (1 mark): Complete combustion of 1.00 g of a hydrocarbon gives 3.38 g carbon dioxide. What is the empirical formula of the hydrocarbon? A CH B CH2 C C2H5 D C3H8 Your answ
- November 2020, AS Paper 1, Q22(c) (5 marks): Bromine reacts with fluorine to form compound A. Compound A is a liquid at room temperature and pressure but can easily be vaporised. When vaporised, 0.428 g of
- June 2019, Paper 2, Q21 (6 marks): 21* Analysis of an unknown organic compound produced the following results. Elemental analysis by mass C: 73.17%; H: 7.32%; O: 19.51% Mass spectrum Molecular io
- June 2019, Paper 3, Q3(a)(ii) (1 mark): The student uses safety glasses and a lab coat. State, with a reason, one other important safety precaution the student should take when carrying out this exper
- June 2019, Paper 3, Q3(a)(iii) (2 marks): 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 c
- June 2019, Paper 3, Q3(a)(iv) (2 marks): The student makes suitable modifications to the method and repeats the experiment to obtain the accurate results shown below. Mass of dish / g 8.364 Mass of dis
- June 2019, AS Paper 1, Q3 (1 mark): What is the percentage composition by mass of nitrogen in (NH4)2CO3? A 14.58% B 17.95% C 29.17% D 37.50% Your answer [1]
- June 2019, AS Paper 1, Q25(b)(iii) (3 marks): Organic compound E is formed by the substitution of some of the H atoms in butane by Cl atoms. A chemist found that 0.636 g of compound E has a volume of 78.0 c
- June 2018, Paper 1, Q20(c) (4 marks): Compound A is an oxide of chlorine that is a liquid at room temperature and pressure and has a boiling point of 83 °C. When 0.4485 g of A is heated to 100 °C at
- June 2018, Paper 2, Q22(c)(i) (5 marks): Compound N is a fuel additive containing carbon, hydrogen and oxygen only. Complete combustion of 1.71 g of compound N produces 2.97 g of CO2 and 1.62 g of H2O.
- June 2018, Paper 2, Q22(d) (6 marks): The relative molecular masses and boiling points of some fuels are shown in Table 22.1. Fuel Relative molecular mass Boiling point / °C hexane 86 69 pentan-1-ol
- June 2018, AS Paper 1, Q3 (1 mark): A compound has the composition by mass: H, 5.00%; N, 35.00%; O, 60.00%. Which compound has this composition? A HNO3 B NH4NO3 C HNO2 D NH2OH Your answer [1]
- June 2018, AS Paper 2, Q7 (6 marks): 7* Compound F is a trans stereoisomer which is a useful intermediate in organic synthesis. The results of elemental and spectral analysis of compound F are show
- June 2017, Paper 1, Q4 (1 mark): Which calcium compound contains the greatest percentage by mass of calcium? A calcium carbonate B calcium nitrate C calcium hydroxide D calcium sulfate Your ans
- June 2017, Paper 1, Q23(b) (6 marks): This question is about reactions of ions and compounds of transition elements. (b)* A hydrated nickel(II) complex, A, is heated in a crucible to remove the wate
- June 2017, Paper 2, Q3 (1 mark): Complete combustion of an organic compound forms 40 cm3 of carbon dioxide and 40 cm3 of 3 water vapour, under the same conditions of temperature and pressure. W
- June 2017, Paper 2, Q20(a) (3 marks): The percentage composition and mass spectrum of the compound are shown below. Percentage composition by mass: C, 70.58%; H, 5.92%; O, 23.50%. Mass spectrum 100
- June 2017, AS Paper 1, Q2 (1 mark): An organic compound has the composition by mass: C, 53.33 %; H, 11.11%; O, 35.56%. What is the empirical formula of the organic compound? A C4H8O2 B C4H10O2 C C
- June 2017, AS Paper 1, Q25(b) (5 marks): An alkene D is a liquid at room temperature and pressure but can easily be vaporised. When vaporised, 0.1881 g of D produces 82.5 cm3 of gas at 101 kPa and 373
- June 2016, AS Paper 1, Q26(c)(i) (1 mark): What is the empirical formula of compound F? [1]
- June 2016, AS Paper 2, Q7 (6 marks): 7* Organic compound C has the following percentage composition by mass: C, 54.5%; H, 9.1%; O, 36.4%. The infrared spectrum and mass spectrum of compound C are s
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