Lesson 3.1.2.4

3.1.2.4 Empirical and molecular formula Quiz: AQA Chemistry, Unit 1

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.1.2.4, Empirical and molecular formula: 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. What is an empirical formula?

    • The simplest whole number ratio of atoms of each element in a compound
    • The mass of one mole of the compound
    • The ratio of the masses of the elements in the compound
    • The actual number of atoms of each element in one molecule

  2. What is a molecular formula?

    • The simplest whole number ratio of atoms in the compound
    • The actual number of atoms of each element in one molecule
    • The ratio of moles of gas in a balanced reaction
    • The relative formula mass of the compound in grams

  3. Which compound has the empirical formula CH2?

    • C2H6
    • C2H4
    • CH4
    • C3H8

  4. What is the empirical formula of glucose, C6H12O6?

    • C6H12O
    • CHO
    • CH2O
    • C2H4O2

  5. Which statement describes the relationship between molecular and empirical formulas?

    • The molecular formula is always half the empirical formula
    • The molecular formula is a whole number multiple of the empirical formula
    • The molecular formula has no relationship to the empirical formula
    • The molecular formula is always the same as the empirical formula

  6. Which statement about calculating an empirical formula is correct?

    • Use the mole ratio of the reactants only, then convert the answer back into mass in grams
    • Convert the mass or percentage composition to moles, then divide by the smallest number of moles
    • Multiply each mass by the relative atomic mass of the element, then divide by the total mass
    • Divide each mass by the Mr of the compound, then multiply by the number of elements present

  7. A compound has Mr = 60 and empirical formula CH2O. What is its molecular formula?

    • C2H4O2
    • C3H6O3
    • C4H8O4
    • CH2O

  8. A compound contains 40.0% C, 6.7% H and 53.3% O by mass. What is its empirical formula?

    • CHO2
    • C2H4O2
    • CH4O
    • CH2O

  9. A compound contains 2.40 g of magnesium and 1.60 g of oxygen. What is its empirical formula?

    • MgO2
    • Mg3O2
    • Mg2O
    • MgO

  10. A compound contains 52.2% C, 13.0% H and 34.8% O by mass. What is its empirical formula?

    • C4H12O2
    • CH3O
    • C2H3O
    • C2H6O

  11. A compound has empirical formula CH and Mr = 78. What is its molecular formula? (Ar: C = 12, H = 1)

    • C6H6
    • C4H4
    • C2H2
    • CH

  12. A compound contains 0.12 g of carbon and 0.02 g of hydrogen. What is its empirical formula?

    • CH2
    • CH
    • CH4
    • C2H

  13. A hydrocarbon has empirical formula CH2 and Mr = 56. What is its molecular formula?

    • C3H6
    • C5H10
    • C2H4
    • C4H8

  14. A 3.20 g sample of an element forms 4.00 g of its oxide. What is the mass of oxygen combined with it?

    • 1.20 g
    • 7.20 g
    • 3.20 g
    • 0.80 g

  15. What is the empirical formula of ethane, C2H6?

    • C2H6
    • CH3
    • C3H9
    • C2H3

  16. A compound contains 85.7% C and 14.3% H by mass and has Mr = 56. What is its molecular formula?

    • C4H8
    • C2H4
    • C6H12
    • C3H6

  17. A compound has empirical formula C2H5 and Mr = 58. What is its molecular formula?

    • C6H15
    • C2H5
    • C3H7
    • C4H10

  18. A compound contains 1.20 g of carbon, 0.20 g of hydrogen and 0.80 g of oxygen. What is its empirical formula?

    • C2H4O
    • CH2O
    • C2H4O2
    • C4H8O

  19. Why must the empirical formula be calculated before the molecular formula when Mr is not given?

    • Composition data always give the molecular formula directly, without needing Mr or other data
    • It shows the bond angles in the molecule, which can then be used to find the formula
    • It gives the exact molecular mass directly, so no further calculation is needed at all
    • It gives the simplest ratio, which is the only information composition data can supply

  20. A compound contains 49.3% C, 6.9% H and 43.8% O by mass. What is its empirical formula? (Ar: C = 12, H = 1, O = 16)

    • CH2O
    • C2H4O
    • C3H5O2
    • C3H6O2

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