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Edexcel A Level Chemistry

Empirical and Molecular Formulae

Empirical and molecular formulae connect experimental composition data with the actual formula of a compound. These pages build from finding the simplest whole-number ratio of atoms through to using relative molecular mass to scale up to the true molecular formula.

Exam Paper
Paper 1
9CH0/01
Specification Points
5.4 – 5.5
2 points covered
Sub-topics
2 lessons
Revision notes available
Exam Board
Edexcel
Pearson 9CH0

Revision Notes

2 revision notes, in the order the specification teaches them.

A single repeating unit lifted from a pattern
1

Empirical Formulae

Revise how to convert masses, percentages or combustion data into mole ratios and then into the simplest whole-number formula.

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A whole molecule beside its simplest repeating unit
2

Molecular Formulae

Learn how the empirical formula mass and relative molecular mass are used to find the molecular formula of a compound.

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Summary Map

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Summary map

Download, print and revise the key facts of this topic at a glance.

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Summary map · PDF

Empirical and Molecular Formulae Map

Edexcel A Level Chemistry · Topic 5 Formulae, Equations and Amounts of Substance · Empirical and Molecular Formulae

The whole section on one A4 page: empirical formulae from masses and percentages, awkward ratios, molecular formulae and combustion analysis.

Download the map6 key ideas + a data table · A4 portrait · print ready

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Specification

Every specification point in this topic, in the exam board's own words. Rate how confident you are with each one.

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5.1

  1. 5.1

    know that the mole (mol) is the unit for amount of a substance

    Revise

5.2

  1. 5.2

    be able to use the Avogadro constant, L, (6.02 × 1023 mol-1) in calculations

    Revise

5.3

  1. 5.3

    know that the molar mass of a substance is the mass per mole of the substance in g mol-1

    Revise

5.4

  1. a

    know what is meant by empirical formula

    Revise
  2. b

    know what is meant by molecular formula

    Revise

5.5

  1. a

    be able to use experimental data to calculate empirical formulae

    Revise
  2. b

    be able to use experimental data to calculate molecular formulae

    Revise
  3. c

    be able to use pV = nRT for gases and volatile liquids in empirical/molecular formula calculations

    Revise
  4. d

    know that empirical formula calculations may involve composition by mass data

    Revise
  5. e

    know that empirical formula calculations may involve percentage composition by mass data

    Revise

5.6

  1. a

    be able to write balanced full equations, including state symbols, for chemical reactions

    Revise
  2. b

    be able to write balanced ionic equations, including state symbols, for chemical reactions

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5.7

  1. a

    be able to calculate amounts of substance in reactions involving mass

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  2. b

    be able to calculate amounts of substance in reactions involving volume of gas

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  3. c

    be able to calculate amounts of substance in reactions involving volume of solution

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  4. d

    be able to calculate amounts of substance in reactions involving concentration

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  5. e

    know these calculations may involve reactants

    Revise
  6. f

    know these calculations may involve products

    Revise

5.8

  1. 5.8

    be able to calculate reacting masses from chemical equations, and vice versa, using the concepts of amount of substance and molar mass

    Revise

5.9

  1. 5.9

    be able to calculate reacting volumes of gases from chemical equations, and vice versa, using the concepts of amount of substance

    Revise

5.10

  1. 5.10

    be able to calculate reacting volumes of gases from chemical equations, and vice versa, using the concepts of molar volume of gases

    Revise

5.11

  1. a

    be able to calculate solution concentrations in mol dm-3

    Revise
  2. b

    be able to calculate solution concentrations in g dm-3

    Revise
  3. c

    be able to carry out simple acid-base titration calculations using a range of acids, alkalis and indicators

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  4. d

    know the use of phenolphthalein as an indicator

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  5. e

    know the use of methyl orange as an indicator

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5.12

  1. i

    be able to: calculate measurement uncertainties and measurement errors in experimental results

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  2. ii

    be able to: comment on sources of error in experimental procedures

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5.13

  1. 5.13

    understand how to minimise the percentage error and percentage uncertainty in experiments involving measurements

    Revise

5.14

  1. a

    be able to calculate percentage yields using chemical equations and experimental results

    Revise
  2. b

    be able to calculate percentage atom economies using chemical equations and experimental results

    Revise
  3. c

    know that atom economy = molar mass of desired product × 100% / sum of molar masses of all products

    Revise

5.15

  1. i

    be able to relate ionic and full equations, with state symbols, to observations from simple test tube reactions, to include: displacement reactions

    Revise
  2. ii

    be able to relate ionic and full equations, with state symbols, to observations from simple test tube reactions, to include: reactions of acids

    Revise
  3. iii

    be able to relate ionic and full equations, with state symbols, to observations from simple test tube reactions, to include: precipitation reactions

    Revise

5.16

  1. a

    understand risks in practical procedures

    Revise
  2. b

    understand hazards in practical procedures

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  3. c

    suggest appropriate precautions where necessary

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