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Edexcel International 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 Unit
Unit 1
WCH11/01 – IAS
Specification Points
1.1 – 1.6
2 points covered
Sub-topics
2 lessons
Revision notes available
Exam Board
Edexcel IAL
Pearson International

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

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

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 International A Level Chemistry · Unit 1 · Topic 1D 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 worked-compounds 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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1.1

  1. a

    know the term 'atom'

    Revise
  2. b

    know the term 'element'

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  3. c

    know the term 'ion'

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  4. d

    know the term 'molecule'

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  5. e

    know the term 'compound'

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  6. f

    know the term 'empirical formula'

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  7. g

    know the term 'molecular formula'

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1.2

  1. a

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

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  2. b

    be able to perform calculations using the Avogadro constant L (6.02 x 10^23 mol-1)

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1.3

  1. a

    write balanced full equations, including state symbols, for chemical reactions

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  2. b

    write balanced ionic equations, including state symbols, for chemical reactions

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1.4

  1. i

    understand the term 'relative atomic mass'

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  2. ii a

    understand the term 'relative molecular mass', including calculating this value from relative atomic masses

    Revise
  3. ii b

    understand the term 'relative formula mass', including calculating this value from relative atomic masses

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  4. ii c

    know that the term 'relative formula mass' should be used for compounds with giant structures

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  5. iii

    understand the term 'molar mass'

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  6. iv

    understand the terms: parts per million (ppm), including gases in the atmosphere

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1.5

  1. a

    calculate the concentration of a solution in mol dm−3

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  2. b

    calculate the concentration of a solution in g dm−3

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  3. c

    know that titration calculations are not required at this stage

1.6

  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

1.7

  1. a

    be able to use chemical equations to calculate reacting masses using the concepts of amount of substance and molar mass

    Revise
  2. b

    be able to use reacting masses to calculate chemical quantities from equations using the concepts of amount of substance and molar mass

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1.8

  1. i

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

    Revise
  2. ii

    be able to use chemical equations to calculate volumes of gases and vice versa, using: the molar volume of gases

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  3. iii

    be able to use chemical equations to calculate volumes of gases and vice versa, using: the expression pV = nRT for gases and volatile liquids

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1.9

  1. a

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

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  2. b

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

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  3. c

    be able to calculate percentage atom economies by mass in laboratory processes using chemical equations and experimental results

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  4. d

    be able to calculate percentage atom economies by mass in industrial processes using chemical equations and experimental results

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  5. e

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

    Revise

1.10

  1. a

    be able to determine a formula by experiment, including evaluation of the data

    Revise
  2. b

    be able to confirm an equation by experiment, including evaluation of the data

1.11

  1. 1.11

    CORE PRACTICAL 1 Measurement of the molar volume of a gas.

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1.12

  1. i

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

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  2. ii

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

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  3. iii

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

    Revise