5.3.1.1 Conservation of mass and balanced chemical equations Quiz: AQA Combined Science, Unit 10

The 20 questions

1. What does the law of conservation of mass state about any chemical reaction?

   • Mass is conserved
   • Mass always decreases
   • Mass changes unpredictably
   • Mass always increases

2. Why must a balanced symbol equation have equal numbers of each atom type?

   • Atoms are destroyed
   • Molecules are conserved
   • Atoms are conserved
   • Atoms are created

3. Which equation is balanced for magnesium burning in oxygen?

   • Mg + O2 -> MgO
   • 2Mg + 2O2 -> 2MgO
   • 2Mg + O2 -> 2MgO
   • Mg2 + O2 -> MgO

4. Which equation is balanced for nitrogen reacting with hydrogen?

   • N2 + H2 -> NH3
   • 2N2 + H2 -> NH3
   • N2 + 2H2 -> NH3
   • N2 + 3H2 -> 2NH3

5. Which equation correctly balances Ca + HCl -> CaCl2 + H2?

   • Ca + HCl -> CaCl2 + H2
   • Ca + 2HCl -> CaCl2 + H2
   • Ca + 2HCl -> CaCl + H2
   • 2Ca + HCl -> CaCl2 + H2

6. In the chemical formula CO2, what does the subscript 2 indicate?

   • Total atoms
   • Two molecules
   • Two carbon atoms
   • Two oxygen atoms

7. A 5.0 g sample of magnesium burns completely in 3.3 g of oxygen. What mass of magnesium oxide forms?

   • 8.0 g
   • 8.3 g
   • 1.7 g
   • 5.0 g

8. In a sealed flask, 2.0 g of reactant X and 6.0 g of reactant Y react completely to form only product Z. What is the mass of Z?

   • 6.0 g
   • 12.0 g
   • 8.0 g
   • 4.0 g

9. Why might the mass of an open flask appear to decrease during a reaction?

   • Volume decreased
   • A gas escaped
   • Energy was lost
   • Atoms were destroyed

10. In a balanced chemical equation, what must be equal on both sides?

    • State symbols
    • Total volume
    • Number of molecules
    • Number of atoms

11. Which set of coefficients balances Fe2O3 + C -> Fe + CO2?

    • Fe2O3 + 3C -> 2Fe + 3CO2
    • 2Fe2O3 + 3C -> 4Fe + 3CO2
    • 2Fe2O3 + 3C -> 2Fe + 3CO2
    • 2Fe2O3 + C -> 4Fe + CO2

12. In the equation CH4 + 2O2 -> CO2 + 2H2O, how many oxygen atoms are on the reactant side?

    • 2
    • 8
    • 6
    • 4

13. What is the main purpose of a balanced chemical symbol equation?

    • Calculate density
    • Show reacting quantities
    • Measure temperature
    • Find reaction rate

14. In the term 3H2O, what does the large multiplier 3 represent?

    • Three oxygen atoms
    • Three water molecules
    • Three hydrogen atoms
    • Three ions

15. In the reaction 2Na + Cl2 -> 2NaCl, what is the ratio of sodium atoms to chlorine molecules?

    • 2 : 1
    • 1 : 2
    • 2 : 2
    • 1 : 1

16. Which equation shows the decomposition of calcium carbonate with atoms conserved?

    • CaCO3 -> Ca + CO2
    • CaCO3 -> CaO + O2
    • CaCO3 -> CaO2 + C
    • CaCO3 -> CaO + CO2

17. Which equation is balanced for the complete combustion of methane?

    • CH4 + O2 -> CO2 + H2O
    • 2CH4 + O2 -> 2CO2 + H2O
    • CH4 + 2O2 -> CO2 + 2H2O
    • CH4 + O2 -> CO2 + 2H2O

18. Zinc and sulfur react in a sealed tube, with 6.5 g of zinc reacting with 3.2 g of sulfur. What mass of zinc sulfide forms?

    • 3.2 g
    • 6.5 g
    • 9.7 g
    • 16.2 g

19. Where is a multiplier written in a chemical equation compared to a subscript?

    • Above the symbol
    • After the formula
    • Before the formula
    • Below the symbol

20. When 24.5 g of potassium chlorate decomposes in a closed flask, what mass of potassium chloride forms? (Mr: KClO3 122.5, KCl 74.5, O2 32)

    • 7.45 g
    • 9.6 g
    • 24.5 g
    • 14.9 g

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