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Year 10 Chemistry: Moles and relative formula mass lesson pack

A complete, ready-to-teach GCSE lesson on moles and relative formula mass. Below is a real sample of what ChalkHour makes: the full pack adds three levels of worksheet, model answers, a teaching explainer and print-ready PDF and Word files.

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Real sample

Moles and Relative Formula Mass

This lesson introduces the fundamental chemical concept of the mole and its relationship with relative formula mass. Students will learn to calculate Mr and use the mole equation to convert between mass and amount of substance.

Learning objectives

  • Calculate the relative formula mass (Mr) of a compound using relative atomic masses (Ar).
  • Define a mole as the unit for amount of substance and state the value of the Avogadro constant.
  • Use the formula 'moles = mass / Mr' to calculate the number of moles in a given mass.
  • Rearrange the mole equation to calculate mass from a given number of moles.

Lesson plan (60 minutes)

  1. Introduction · 5 min

    Do Now: Recall relative atomic mass (Ar) for O, Mg, C, and Cl using a periodic table.

  2. Direct Instruction · 15 min

    Teacher-led explanation: How to calculate Mr and the definition of a mole. Shared worked example.

  3. Guided Practice · 10 min

    Guided Practice: Students calculate Mr for water, carbon dioxide, and sodium chloride. Independent check.

  4. Independent Practice · 20 min

    Differentiated Worksheet Task: Students complete Support, Core, or Stretch worksheets based on prior attainment.

  5. Plenary/Assessment · 10 min

    Multiple Choice Quiz: Check for understanding across the whole class.

Key vocabulary

Relative Atomic Mass (Ar)
The average mass of an atom of an element compared to 1/12th the mass of an atom of carbon-12.
Relative Formula Mass (Mr)
The sum of the relative atomic masses of the atoms in the numbers shown in the formula.
Mole
The unit for the amount of substance; one mole contains 6.02 x 10^23 particles.
Avogadro Constant
6.02 x 10^23; the number of atoms, molecules, or ions in one mole of a substance.
Mass
The weight of a sample measured in grams (g).

Core worksheet (first questions)

  1. Calculate the Mr of calcium carbonate (CaCO3). [Ar: Ca=40, C=12, O=16]
  2. Calculate the Mr of sodium carbonate (Na2CO3). [Ar: Na=23, C=12, O=16]
  3. Calculate the Mr of iron(III) oxide (Fe2O3). [Ar: Fe=56, O=16]
  4. Calculate the number of moles in 60g of Magnesium Oxide (MgO). [Ar: Mg=24, O=16]

Quiz (sample)

  1. 1. What is the definition of relative formula mass (Mr)?

    • A. The mass of one atom of the element.
    • B. The sum of the relative atomic masses of the atoms in the formula.
    • C. The number of protons in the nucleus.
    • D. The mass of 1cm3 of the substance.

  2. 2. What is the Mr of MgO? (Ar: Mg=24, O=16)

    • A. 20
    • B. 40
    • C. 56
    • D. 80

  3. 3. What is the value of the Avogadro constant?

    • A. 6.02 x 10^22
    • B. 6.02 x 10^23
    • C. 6.02 x 10^-23
    • D. 1.66 x 10^-24

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