Year 9 · Science

Conservation of mass calculations: Year 9 GCSE bridge

6 checked activities 3 video matches

Start here

Focus on conservation of mass in chemical reactions. Start with “Apply Relative Formula Mass to Prove Conservation of Mass in Reactions”, then explain the idea in your own words.

Understand the key idea

Because atoms are only rearranged, the total mass of reactants equals the total mass of products. This lets you calculate a missing mass: if you know the mass of every substance but one, subtract the known product masses from the total reactant mass. Reactions that appear to gain or lose mass in an open container involve a gas entering or escaping.

Common mix-up

A metal gaining mass when it burns does not break conservation of mass. Oxygen from the air has joined the metal, so the sealed-system total is still unchanged.

Try this first

Calculate the missing product mass from a reaction table.
Explain why magnesium gains mass when it burns.
Decide whether an open or closed system is needed to show conservation.

Ask: Magnesium gets heavier when it burns — how can that not break the rule?

Year 9 learners practise conservation of mass in chemical reactions.

The activities include Apply Relative Formula Mass to Prove Conservation of Mass in Reactions, Apply the Law of Conservation of Mass in Open and Closed Systems, Apply the Law of Conservation of Mass to Solve Calculations, and related practice. The checked support below includes video, worksheet, teaching. Open a resource in its provider's website and choose the format that best helps the learner explain the idea independently.

Activities covered

Apply Relative Formula Mass to Prove Conservation of Mass in Reactions
Apply the Law of Conservation of Mass in Open and Closed Systems
Apply the Law of Conservation of Mass to Solve Calculations
Calculate Relative Formula Mass
Understand the Law of Conservation of Mass
Understand the Law of Conservation of Mass in Terms of Atoms

Learning path

These same-subject links were reviewed as the foundations for this topic and the learning it directly unlocks.

Learn this first

Year 8Conservation Of Mass
Secures conservation in reactions before Year 9 uses the rule to calculate unknown masses.
Year 8Rearrangement Of Atoms In Reactions
Provides the atom-rearrangement explanation for why total mass remains constant.

Where this leads next

Year 10 / GCSEChemistry: Chemical Measurements
GCSE quantitative chemistry applies conservation to measured masses and reacting quantities.
Year 10 / GCSEChemistry: Chemical Changes
Uses conserved atoms and mass when representing and analysing chemical changes.

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