plumiEmpirical and molecular formulae: Edexcel International A Level Chemistry questions
Edexcel International A Level Chemistry past-paper questions on 1.2.1 Empirical and molecular formulae, 2019–2025, with mark schemes and examiner’s reports where available.
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All 58 questions on Empirical and molecular formulae, as a list
- June 2025, AS Unit 1, Q12 (1 mark): A 3.50 g sample of an organic compound will completely burn forming 5.15 g of carbon dioxide and 2.11 g of water. What is the empirical formula of the compound?
- June 2025, AS Unit 2, Q16(b) (2 marks): A sample of cyclohexanol contains 7.13 g of carbon, 1.19 g of hydrogen and 1.58 g of oxygen. Show that this data is consistent with the empirical formula C6H12O
- June 2025 (A), Unit 5, Q19(b)(ii) (3 marks): Determine the molecular formula of E, using the data shown and the information in (b). (3) % carbon % hydrogen % nitrogen % oxygen 51.1 8.51 15.1
- January 2025, AS Unit 1, Q7 (1 mark): A sample of hydrated magnesium sulfate contains 43% by mass of water. What is the formula of this magnesium sulfate? A MgSO4•9H2O B MgSO4•5H2O C MgSO4•2.5H2O D
- January 2025, AS Unit 1, Q24(a)(iii) (2 marks): Compound X contains 85.7 % carbon and 14.3 % hydrogen by mass. Calculate the empirical formula of X. (2)
- January 2025, AS Unit 1, Q24(a)(iv) (1 mark): Deduce the molecular formula of X. (1)
- January 2025, Unit 5, Q12 (1 mark): An 8.4 g sample of a hydrocarbon formed 26.4 g of carbon dioxide on complete combustion. What is the molecular formula of this compound? A CH2 B C6H6 C C2H6 D C
- January 2025, Unit 5, Q20(b)(ii) (4 marks): The double salt also exists as hydrated crystals. When a sample of the hydrated double salt is heated until all the water of crystallisation is removed, 56.74 %
- January 2025, Unit 6, Q3(b) (4 marks): Complete combustion of 4.70 g of X produces 13.80 g of carbon dioxide and 2.82 g of water. Determine the empirical formula of X. (4)
- October 2024, AS Unit 1, Q18(d)(iii) (3 marks): One of the chlorinated compounds contains 44.1% carbon and 6.9% hydrogen by mass. Calculate the molecular formula of this compound. (3)
- October 2024, AS Unit 2, Q16(a)(ii) (3 marks): Calculate the number of water molecules of crystallisation, x, in the formula of this sample of hydrated magnesium sulfate. (3)
- October 2024, AS Unit 2, Q20(d)(i) (3 marks): Calculate the molar ratio of Al : Li in this alloy. (3)
- October 2024, Unit 4, Q20(e)(ii) (3 marks): All of the barium carbonate reacted and produced 6.19 g of hydrated barium chloride. Calculate the relative formula mass of BaCl2 • nH2O and hence deduce the va
- June 2024, AS Unit 1, Q18(b)(i) (2 marks): The acidic derivative of tartaric acid contains 20.8% potassium, 25.5% carbon, 2.66% hydrogen by mass and the rest is oxygen. Calculate the empirical formula. (
- June 2024, AS Unit 2, Q18(b)(iv) (4 marks): Compound A has Mr = 84.5, and a composition by mass of H = 1.18 %, Cl = 42.01 % and the remainder is oxygen. Deduce the molecular formula of compound A, showing
- June 2024, Unit 5, Q19(d) (5 marks): Poly(ethenol) is made from a polymer intermediate, rather than by polymerisation, as ethenol is unstable. The polymer intermediate is prepared from a monomer, X
- June 2024 (R), AS Unit 2, Q20(a)(i) (3 marks): Calculate the empirical formula of acetoin. You must show all your working. (3)
- June 2024 (R), AS Unit 2, Q20(a)(ii) (1 mark): The molar mass of acetoin is 88.0 g mol–1. Use this information to calculate the molecular formula of acetoin. (1)
- January 2024, AS Unit 1, Q21(a) (4 marks): Boric acid contains 17.48% by mass of boron, 77.67% of oxygen and the remainder is hydrogen. The molar mass of boric acid is 61.8 g mol–1. [Ar values: H = 1 B =
- January 2024, Unit 5, Q17(c)(i) (3 marks): Calculate the values x, y and z in Reinecke’s salt. You must show your working. (3)
- October 2023, AS Unit 2, Q21(a)(i) (3 marks): Use these data to calculate the empirical formula of X. (3)
- October 2023, AS Unit 2, Q21(a)(ii) (2 marks): The mass spectrum of X is shown. 100 80 60 Percentage relative 40 abundance 20 0.0 30 40 50 60 70 80 90 m / z Deduce the molecular formula of X, using the mass
- October 2023, Unit 5, Q19(a) (2 marks): A compound of iron contains, by mass, 39.5% potassium, 28.2% iron and 32.3% oxygen. Calculate the empirical formula of this compound. (2)
- June 2023, AS Unit 2, Q22(e) (4 marks): Borax is another cleaning agent used to remove limescale. Borax is a compound of sodium, boron and oxygen. Borax crystals contain water of crystallisation. The
- January 2023, AS Unit 1, Q3 (1 mark): A sample of 15.0 g of vanadium reacted completely with 7.07 g of oxygen. What is the formula of the oxide? [Ar values: V = 50.9 O = 16.0] A VO B V2O3 C VO2 D V2
- January 2023, Unit 4, Q18(b)(ii) (1 mark): Lactic acid is converted into compound X which is then polymerised to form PLA. The empirical formula of X is C3H4O2 and its molar mass is 144 g mol–1. Determin
- January 2023, Unit 5, Q18(c) (3 marks): Hydrated potassium vanadium(III) sulfate contains 7.9 % potassium, 10.2 % vanadium, 12.9 % sulfur, 4.8 % hydrogen and 64.2 % oxygen. Calculate the empirical for
- October 2022, AS Unit 1, Q15(d)(i) (2 marks): Calculate the empirical formula of compound X. You must show all your working. (2)
- October 2022, AS Unit 1, Q15(d)(iii) (1 mark): Deduce the molecular formula of compound X, using your answers to (d)(i) and (d)(ii). (1)
- October 2022, Unit 5, Q22(a) (4 marks): Viridian is a blue‑green pigment with the formula M2O3·2H2O ; M is not the symbol of the element. When a sample of viridian is heated until all the water of cry
- October 2022, Unit 5, Q23(a) (4 marks): Calculate the percentage composition by mass of the elements in salicin. (4)
- June 2022, AS Unit 1, Q19(b) (4 marks): The concentration of the solution obtained in (a) is increased by heating it gently to remove some of the water. The solution is allowed to cool and pale green
- June 2022, Unit 5, Q7(a) (1 mark): A repeat unit of the polymer PET has the structure shown. O O O O What is the percentage by mass of carbon in the repeat unit? (1) A 57.1 % B 62.5 % C 65.2 % D
- June 2022, Unit 5, Q14(a) (4 marks): Complete combustion of 6.02 g of Q produces 18.07 g of carbon dioxide and 3.30 g of water. Determine the empirical formula of Q. (4)
- January 2022, AS Unit 1, Q19(a)(i) (1 mark): Complete the table of results. (1) Measurement Mass / g Mass of empty crucible 21.21 Mass of crucible and hydrated 26.71 magnesium sulfate before heating Mass o
- January 2022, AS Unit 1, Q19(a)(ii) (4 marks): Use these results to calculate the value of x in MgSO4 · x H2O. Give your answer to the nearest whole number. [Ar values: H = 1.0 O = 16.0 Mg = 24.3 S = 32.1] (
- January 2022, AS Unit 3, Q2(a)(i) (2 marks): State the measurements that should be made. (2)
- January 2022, AS Unit 3, Q2(a)(ii) (2 marks): Give two reasons why pure O2(g), and not air, should be used. (2)
- January 2022, AS Unit 3, Q2(a)(iii) (3 marks): The experiment showed that 1.33 g of X contains 0.14 g of hydrogen and 0.63 g of carbon. Calculate the empirical formula of X, using these data. You must show y
- January 2022, Unit 4, Q20(b)(i) (3 marks): Compound A is thought to be another isomer of hexanoic acid. 10 g of compound A is found to contain 6.21 g of carbon and 1.03 g of hydrogen, with the remainder
- January 2022, Unit 5, Q16(c) (6 marks): Hydrated calcium benzoate is used as a preservative in soft drinks. It has the formula Ca(C6H5COO)2·xH2O. 2.60 g of hydrated calcium benzoate was dissolved in d
- October 2021, AS Unit 1, Q13(c) (3 marks): Calcium silicate is formed in the removal of silicon dioxide impurities in the extraction of iron from its ores. A sample of calcium silicate composed of calciu
- October 2021, Unit 4, Q16(a)(ii) (5 marks): Show that the empirical formula of X is C4H6O3 . You must show your working. (5)
- October 2021, Unit 5, Q18(a) (2 marks): Deduce the formula of the hydrated salt A. You must show your working. (2)
- October 2021, Unit 5, Q18(d) (3 marks): The percentage composition by mass of salt E is K = 35.6 % Fe = 17.0 % C = 21.9 % N = 25.5 % Calculate the empirical formula of salt E. (3)
- June 2021, AS Unit 1, Q17 (1 mark): An oxide of lead contains 90.7 % by mass of lead. What is the formula of this oxide? [Ar values: O = 16.0 Pb = 207.2] A PbO B PbO2 C Pb2O3 D Pb3O4
- June 2021, AS Unit 1, Q24(d) (3 marks): 25.00 g of a compound contains 6.98 g of iron and 6.03 g of sulfur. The remaining mass is oxygen. Calculate the empirical formula of this compound. [Ar values:
- June 2021, Unit 4, Q17(a) (2 marks): Y contains 66.7% carbon, 11.1% hydrogen and 22.2% oxygen by mass. Show that these data are consistent with its molecular formula. (2)
- June 2021, Unit 5, Q19(b)(iii) (3 marks): Analysis of Y showed that its composition by mass was 62.6 % carbon; 11.3 % hydrogen; 12.2 % nitrogen; 13.9 % oxygen. Determine the empirical formula of Y. You
- June 2021, Unit 6, Q3(d)(ii) (4 marks): Calculate the empirical formula of the compound, using the data given. You must show your working. (4)
- June 2021, Unit 6, Q3(d)(iv) (1 mark): Deduce the molecular formula of the compound, using your answers to (ii) and (d)(iii). (1)
- October 2020, AS Unit 1, Q4 (1 mark): A compound has Mr = 84 and its composition by mass is 71.4 % carbon, 9.6 % hydrogen and 19.0 % oxygen. What is the molecular formula of this compound? [ Ar valu
- October 2020, Unit 4, Q13 (1 mark): In which of these esters is the percentage by mass of carbon 54.5 %? A methyl methanoate, HCOOCH3 B methyl ethanoate, CH3COOCH3 C ethyl ethanoate, CH3COOCH2CH3
- October 2020, Unit 5, Q7 (1 mark): A hydrocarbon contains 91.3 % by mass of carbon. Which of these could be the molecular formula of this compound? A C6H6 B C7H8 C C8H10 D C9H12
- October 2020, Unit 5, Q25(e)(i) (3 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
- January 2020, AS Unit 1, Q21(d)(i) (2 marks): When 10.0 g of ethene reacts completely with oxygen, the mass of compound Y formed is 15.7 g. Calculate the empirical formula of Y. You must show your working.
- June 2019, AS Unit 1, Q6 (1 mark): In 1.31 g of a chloride of titanium, there is 0.528 g of titanium. What is the empirical formula of this titanium chloride? [ Ar values: Ti = 47.9 Cl = 35.5 ] A
- January 2019, AS Unit 1, Q24(b) (3 marks): A sample of a compound is analysed and found to contain only 3.09 g carbon, 0.26 g hydrogen and 9.15 g chlorine. The molar mass of the compound is 97.0 g mol−1.
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