Science 9 · Unit 5: Reactivity · Cambridge Lower Secondary Science Stage 9

Questions

1. 1. When chemicals react, what happens to the atoms?

   • They rearrange to make new substances. None are lost.
   • Some atoms are destroyed.
   • New atoms are made.
   • The atoms change into different elements.
   Check

2. 2. Magnesium reacts with hydrochloric acid. Which salt is made?

   • magnesium oxide
   • magnesium hydride
   • magnesium chloride
   • magnesium sulfate
   Check

3. 3. Mg + 2HCl → MgCl₂ + H₂. How many hydrogen atoms are on each side?

   • 4 on each side
   • 1 on the left and 2 on the right
   • 2 on each side
   • 2 on the left and 1 on the right
   Check

4. 4. Mg + 2HCl → MgCl₂ + H₂. How many chlorine atoms are on each side?

   • 1 on each side
   • 4 on each side
   • 2 on each side
   • 1 on the left and 2 on the right
   Check

5. 5. In oxygen + hydrogen → water, how does the number of hydrogen atoms in the reactants compare with the products?

   • the same as
   • larger than
   • smaller than
   Check

6. 6. Marcus heats 10 g of iron with 6 g of sulfur. What is the mass of the iron sulfide made?

   • 60 g
   • 4 g
   • 16 g
   • 10 g
   Check

7. 7. Zara heats 15 g of iron with 9 g of sulfur. What mass of product does she get?

   • 135 g
   • 24 g
   • 15 g
   • 6 g
   Check

8. 8. Zara adds 30 g of calcium carbonate to 50 g of acid in a sealed flask. What will the balance read at the end?

   • 80 g
   • less than 80 g
   • 20 g
   • 50 g
   Check

9. 9. The products of a reaction contain calcium, chlorine, hydrogen, oxygen and carbon. Which elements were in the reactants?

   • hydrogen and oxygen only
   • carbon only
   • calcium, chlorine, hydrogen, oxygen and carbon
   • calcium and chlorine only
   Check

10. 10. Sulfur + oxygen → sulfur dioxide. What is the symbol equation?

    • S + O → SO
    • S + O₂ → SO
    • S + O₂ → SO₂
    • S₂ + O → SO₂
    Check

11. 11. Which elements are present in magnesium carbonate?

    • magnesium and carbon only
    • magnesium, carbon and hydrogen
    • magnesium, chlorine and oxygen
    • magnesium, carbon and oxygen
    Check

12. 12. Which elements are present in carbon dioxide?

    • carbon, oxygen and hydrogen
    • oxygen only
    • carbon only
    • carbon and oxygen
    Check

13. 13. In the same reaction, where did the hydrogen in the water come from?

    • the hydrochloric acid
    • the magnesium carbonate
    • the air
    • the carbon dioxide
    Check

14. 14. In magnesium carbonate + hydrochloric acid → magnesium chloride + carbon dioxide + water, where did the chlorine in the magnesium chloride come from?

    • the water
    • the hydrochloric acid
    • the air
    • the magnesium carbonate
    Check

15. 15. The products of the magnesium carbonate reaction have a mass of 45 g. What was the mass of the reactants?

    • 22.5 g
    • 45 g
    • less than 45 g
    • 90 g
    Check

16. 16. 25 g of magnesium reacts completely with sulfuric acid. How much magnesium is in the magnesium sulfate?

    • 50 g
    • 25 g
    • 0 g
    • 12.5 g
    Check

17. 17. What does conservation of mass mean?

    • Only solids have mass.
    • Products are always heavier.
    • Mass is lost in every reaction.
    • The total mass of the products equals the total mass of the reactants.
    Check

18. 18. Arun mixes 100 g of zinc and 150 g of sulfuric acid in an open beaker. What should the mass of the products be?

    • 250 g
    • 247 g
    • 150 g
    • 50 g
    Check

19. 19. Arun's open beaker contains 247 g at the end, not 250 g, every time. Why?

    • Hydrogen gas escaped into the air.
    • He made a mistake with the balance.
    • Mass was destroyed.
    • The zinc evaporated.
    Check

20. 20. What should a scientist do when they get an unexpected result?

    • Change the result.
    • Ignore it.
    • Repeat the experiment and look for an explanation.
    • Stop doing science.
    Check