AQA · Chemistry · 8462

GCSE Chemistry: Using moles to balance equations

Quantitative chemistry · AQA GCSE Chemistry (8462), specification point 4.3.2.3. Cards are generated from the exam board's own specification for "Using moles to balance equations", and every card links back to the page it came from. Higher tier only. Specification © AQA — used with attribution.

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  1. How are balancing numbers in a symbol equation calculated from masses?

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    Convert each mass in grams to moles, then convert the numbers of moles to the simplest whole-number ratio.

  2. What is the first step when balancing an equation from reactant and product masses?

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    Convert each mass in grams to an amount in moles (n = m ÷ Mr).

  3. After converting masses to moles, how are the balancing numbers obtained?

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    Divide every mole value by the smallest one to give a simple whole-number ratio; those numbers balance the equation.

  4. Balancing numbers in a symbol equation are the simplest ? ratio of the moles of each substance.

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    whole number

  5. Which equation converts a mass in grams to an amount in moles?

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    moles = mass ÷ relative formula mass (n = m ÷ Mr).

  6. Rearrange n = m ÷ Mr to make mass the subject.

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    m = n × Mr.

  7. 4.8 g Mg reacts with 3.2 g O₂ to form 8.0 g MgO. What is the balanced equation? (Ar: Mg 24, O 16)

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    2Mg + O₂ → 2MgO. Moles: Mg 4.8/24 = 0.2, O₂ 3.2/32 = 0.1, MgO 8.0/40 = 0.2 → ratio 2 : 1 : 2.

  8. In AQA GCSE Chemistry, is using moles to balance equations Foundation or Higher Tier?

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    Higher Tier only.

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