Lesson T2.2.2

T2.2.2 Conservation of mass Quiz: KS3 Chemistry, Unit 2

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson T2.2.2, Conservation of mass: 20 multiple choice questions for the KS3 Chemistry (National Curriculum), Unit 2: Atoms, elements and compounds, written with Revision Ninja.

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The 20 questions

  1. What is conserved during any chemical reaction in a closed system?

    • Total mass
    • Total moles
    • Total temperature
    • Total volume

  2. Why does magnesium gain mass when burned in air to form a powder?

    • Heat added mass
    • Oxygen combined with it
    • Water was absorbed
    • Atoms multiplied

  3. Why does a log lose mass when burned in an open fire?

    • Ash is lighter
    • Gases escaped
    • Atoms were destroyed
    • Energy has mass

  4. A closed flask holds 5 g of reactant that forms a product with no gas escaping. What is the mass of the product?

    • 5 g
    • More than 5 g
    • Less than 5 g
    • 0 g

  5. A student reacts 10 g of A with 8 g of B in a sealed flask. What is the total mass of the products?

    • 20 g
    • 18 g
    • 8 g
    • 10 g

  6. Why must a reaction involving gases be done in a closed container?

    • To increase speed
    • To create pressure
    • To stop gas escaping
    • To heat the gas

  7. Which reaction appears to lose mass in an open beaker?

    • Burning a candle
    • Heating magnesium
    • Rusting an iron nail
    • Dissolving salt

  8. What happens to atoms during a chemical reaction?

    • Turned into energy
    • Created from nothing
    • Rearranged into new substances
    • Destroyed completely

  9. Why does mass decrease in an open beaker when gas is released?

    • Gas escaped to air
    • Volume decreased
    • Mass turned to heat
    • Atoms were destroyed

  10. A student weighs a sealed bag holding reactants totalling 25 g. The reaction happens inside and the bag is weighed again. What should the reading be?

    • 26 g
    • 25 g
    • 24 g
    • 0 g

  11. How should you show conservation of mass for a reaction producing a gas?

    • Heat the mixture strongly
    • Use an open beaker
    • Use a sealed container
    • Add more reactants

  12. Why does an iron nail gain mass as it rusts?

    • Water evaporated
    • Air pressure increased
    • Oxygen added to iron
    • Iron atoms expanded

  13. What is the correct correction if someone says mass is created when a gas forms?

    • Gases have no mass
    • Atoms were created
    • Gas atoms were reactants
    • Mass is never conserved

  14. In a sealed flask 12 g of reactants give 9 g of solid product and a gas. What is the mass of gas formed?

    • 21 g
    • 12 g
    • 3 g
    • 9 g

  15. Which law supports the idea that atoms are rearranged, not destroyed?

    • Conservation of energy
    • Periodic law
    • Ohm's law
    • Conservation of mass

  16. Which physical change shows no overall change of mass in a closed system?

    • Dissolving sugar
    • Evaporating water
    • Burning fuel
    • Melting ice

  17. Iron and sulfur react in a closed container starting at 20 g. What is the final mass?

    • 30 g
    • 20 g
    • 0 g
    • 10 g

  18. Why does flask mass fall when hydrogen peroxide decomposes in an open flask?

    • Water evaporated
    • Energy was lost
    • Atoms were destroyed
    • Oxygen gas escaped

  19. A sealed reaction starts with 50 g. What is the mass after reacting?

    • More than 50 g
    • Zero grams
    • Less than 50 g
    • 50 g

  20. Why does heating copper carbonate in an open tube cause a decrease in mass?

    • Copper evaporated
    • Gas escaped
    • Atoms vanished
    • Solid was destroyed

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