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The Mole

HigherHigher tier onlyCombined & TripleAQAEdexcelOCR

Build confidence in The Mole for GCSE Chemistry with this free worksheet and full mark scheme — Higher-tier exam-style questions with worked answers for AQA, Edexcel and OCR. One mole is 6.02 × 10²³ particles (the Avogadro constant), and the mass of one mole in grams equals the relative formula mass.

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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.

This is a Higher tier only topic, so there's no Foundation paper — only the Higher worksheet and mark scheme below.

Higher

WorksheetHigher · PDFMark SchemeHigher · PDF

Topic overview

The mole is the unit chemists use to count particles. One mole of any substance contains the same number of particles: 6.02 × 10²³, which is the Avogadro constant. This is a Higher-only topic.

The mass of one mole of a substance in grams is numerically equal to its relative formula mass. So one mole of water, Mr = 18, has a mass of 18 g.

The formula linking the three quantities is moles = mass ÷ Mr. It rearranges to give mass = moles × Mr and Mr = mass ÷ moles. Working out which quantity is being asked for, and writing the formula down before substituting, prevents most errors.

Revision notes

The Avogadro constant

One mole of any substance contains 6.02 × 10²³ particles.

Those particles may be atoms, molecules or ions depending on the substance. The number is the same regardless of what the substance is.

Mass and moles

The mass of one mole in grams equals the relative formula mass.

So one mole of carbon dioxide, Mr = 44, has a mass of 44 g. The formula is moles = mass ÷ Mr.

Using the formula

Rearranged: mass = moles × Mr, and Mr = mass ÷ moles.

Always calculate the Mr first, then substitute. Give answers to a sensible number of significant figures, usually matching the data given.

Key points

  • One mole contains 6.02 × 10²³ particles.
  • This is the Avogadro constant.
  • One mole in grams equals the relative formula mass.
  • Moles = mass ÷ Mr.
  • Mass = moles × Mr.
  • Calculate the Mr before substituting.

Worked examples

Example 1

Calculate the number of moles in 36 g of water. Mr of H₂O = 18. [2 marks]

Model answer

Moles = mass ÷ Mr = 36 ÷ 18 (1 mark) = 2 moles (1 mark).

Example 2

Calculate the mass of 0.5 moles of carbon dioxide. Mr of CO₂ = 44. [2 marks]

Model answer

Mass = moles × Mr = 0.5 × 44 (1 mark) = 22 g (1 mark).

Example 3

Calculate the number of moles in 5.6 g of iron. Ar of Fe = 56. [2 marks]

Model answer

Moles = mass ÷ Mr = 5.6 ÷ 56 (1 mark) = 0.1 moles (1 mark).

Common mistakes

  • Multiplying instead of dividing to find moles.

    Moles = mass ÷ Mr. Multiplying gives the mass instead.

  • Forgetting to calculate the Mr first.

    The formula needs the relative formula mass, not the atomic mass of one element.

  • Giving moles a mass unit.

    Moles have the unit mol, not grams.

  • Using the wrong value from the periodic table.

    Use the relative atomic mass, the larger number.

Exam tips

  • Write the formula down before substituting.
  • Calculate the Mr as a separate first step.
  • Check the unit — mol for moles, g for mass.
  • Remember this is a Higher-only topic.

Key terms

Mole
The unit for an amount of substance, containing 6.02 × 10²³ particles.
Avogadro constant
The number of particles in one mole, 6.02 × 10²³.
Relative formula mass
The mass of one mole of a substance in grams.
Amount of substance
A quantity measured in moles.

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Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.