Lesson 3.1.2.1

3.1.2.1 Relative atomic mass and relative molecular mass Quiz: AQA Chemistry, Unit 1

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.1.2.1, Relative atomic mass and relative molecular mass: 20 multiple choice questions for the AQA Chemistry (7405), Unit 1: Physical chemistry, written with Revision Ninja.

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The 20 questions

  1. Relative atomic mass is defined relative to what standard?

    • One twelfth of the mass of one atom of carbon-12
    • The mass of one atom of hydrogen
    • One sixteenth of the mass of one atom of oxygen
    • The mass of one mole of carbon-12 in grams

  2. Which is the correct definition of relative molecular mass?

    • The mean mass of a molecule compared with one twelfth of the mass of a carbon-12 atom
    • The sum of the proton numbers of the atoms present in one molecule of the compound formed
    • The mass of one molecule in kilograms, found from the mass spectrum of a sample of that compound
    • The mass of one mole of molecules in grams, measured directly on a balance for the substance

  3. Which term is used instead of relative molecular mass for ionic compounds?

    • Relative formula mass
    • Molar enthalpy
    • Empirical mass
    • Relative atomic mass

  4. What is the relative molecular mass of CO2? (Ar: C = 12, O = 16)

    • 60
    • 28
    • 44
    • 32

  5. What is the relative formula mass of CaCO3? (Ar: Ca = 40, C = 12, O = 16)

    • 72
    • 100
    • 120
    • 84

  6. Which statement about relative atomic masses is correct?

    • They are measured in atomic mass units for each individual atom, shown on the mass spectrum peak
    • They are always whole numbers for every element, because isotopes do not change the average mass
    • They are dimensionless ratios comparing the average atom mass with one twelfth of carbon-12
    • They are masses in grams of one mole of atoms, which is the same as the molar mass of the element

  7. What is the relative molecular mass of H2SO4? (Ar: H = 1, S = 32, O = 16)

    • 98
    • 114
    • 66
    • 82

  8. What is the relative formula mass of Na2CO3? (Ar: Na = 23, C = 12, O = 16)

    • 94
    • 118
    • 82
    • 106

  9. What is the relative formula mass of Ca(OH)2? (Ar: Ca = 40, O = 16, H = 1)

    • 90
    • 58
    • 64
    • 74

  10. What is the relative formula mass of hydrated copper(II) sulfate, CuSO4.5H2O? (Ar: Cu = 63.5, S = 32, O = 16, H = 1)

    • 264.5
    • 159.5
    • 180.5
    • 249.5

  11. A compound has an empirical formula CH2O (Mr = 30) and a relative molecular mass of 180. What is its molecular formula?

    • C6H12O6
    • C2H4O2
    • C3H6O3
    • C12H24O12

  12. A gas has Mr = 44. What is the mass of 0.5 mol of this gas?

    • 44 g
    • 88 g
    • 11 g
    • 22 g

  13. What is the relative molecular mass of ethanoic acid, CH3COOH? (Ar: C = 12, H = 1, O = 16)

    • 74
    • 30
    • 45
    • 60

  14. What is the relative formula mass of Al2(SO4)3? (Ar: Al = 27, S = 32, O = 16)

    • 315
    • 369
    • 342
    • 406

  15. A mass spectrum of a substance shows a molecular ion peak at m/z = 46. Which substance is consistent with this?

    • Ethanal, CH3CHO
    • Ethanol, C2H5OH
    • Methane, CH4
    • Propane, C3H8

  16. Why is the relative atomic mass of chlorine given as 35.5 rather than 35 or 37?

    • It is the mass of the atoms plus the mass of free electrons in the sample, measured together
    • It is the mass of the most abundant isotope only, which is the isotope found in most samples
    • It is the average of the two mass numbers, found by adding 35 and 37 and dividing by two
    • It is a weighted mean of the isotopes 35Cl and 37Cl present in natural abundance

  17. A mass spectrum of a gas shows a molecular ion peak at m/z = 92. Which formula is consistent with a relative molecular mass of 92?

    • N2O
    • CO2
    • N2O4
    • NO2

  18. A compound has an empirical formula mass of 15 and a relative molecular mass of 90. How many empirical units are in one molecule?

    • 3
    • 5
    • 9
    • 6

  19. Why is relative formula mass used for sodium chloride rather than relative molecular mass?

    • Sodium and chlorine have no relative atomic mass, so the molecular mass cannot be calculated for NaCl
    • NaCl molecules are too heavy to measure accurately, so chemists use a rough estimate of the mass
    • NaCl has a mass of zero in the solid state, because the ions are held in place by the lattice
    • NaCl is an ionic lattice with no discrete molecules, so the formula unit is the basis of the mass

  20. Which row correctly lists the relative molecular masses of CH4, C2H6 and C3H8?

    • 20, 30, 44
    • 16, 30, 44
    • 16, 32, 48
    • 12, 24, 36

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