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The Reactivity Series and Displacement Reactions — Answers

Answer sheet with model answers and success criteria for the Year 11 mixtures & chemical reactions worksheet.

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Success TutoringWorksheetsAnswer sheetYear 11 · Science · Mixtures & Chemical Reactions

The Reactivity Series and Displacement Reactions — Answers

Part A: The reactivity series

The reactivity series lists metals from most to least reactive: potassium, sodium, calcium, magnesium, aluminium, (carbon), zinc, iron, (hydrogen), copper, silver, gold. Carbon and hydrogen are non-metals included for comparison.

Metals above hydrogen react with dilute acids: metal + acid → salt + hydrogen. The most reactive metals also react with cold water: metal + water → metal hydroxide + hydrogen.

1.Which metal would react most vigorously with cold water?
  1. AMagnesium
  2. BPotassium
  3. CZinc
  4. DCopper

Answer: Potassium

Potassium is near the top of the series and reacts violently with cold water.

2.Balance the reaction of calcium with water: Ca + H₂O → Ca(OH)₂ + H₂

Answer: Ca + 2H₂O → Ca(OH)₂ + H₂

  1. Left: Ca 1, H 4, O 2
  2. Right: Ca 1, O 2, H 2 + 2 = 4 (balanced)
3.Write a word equation and a balanced equation for magnesium reacting with hydrochloric acid.

Answer: magnesium + hydrochloric acid → magnesium chloride + hydrogen; Mg + 2HCl → MgCl₂ + H₂

  1. Left: Mg 1, H 2, Cl 2
  2. Right: Mg 1, Cl 2, H 2 (balanced)
4.A student adds copper to dilute hydrochloric acid and sees no bubbles. Explain why.

Answer: Copper is below hydrogen in the reactivity series, so it is not reactive enough to displace hydrogen from the acid.

5.Gold is found in the ground as the pure metal because it is so unreactive.

Answer: True

Unreactive metals such as gold do not readily form compounds, so they can be found native (uncombined).

Part B: Displacement reactions

A more reactive metal will displace (push out) a less reactive metal from a solution of its compound. For example: magnesium + copper(II) sulfate → magnesium sulfate + copper. If the free metal is less reactive, there is no reaction.

6.Zinc is placed in copper(II) sulfate solution. Will a reaction occur? If so, write the word and balanced equations.

Answer: Yes, because zinc is more reactive than copper. zinc + copper(II) sulfate → zinc sulfate + copper; Zn + CuSO₄ → ZnSO₄ + Cu

7.Copper is placed in zinc sulfate solution. Will a reaction occur? Explain.

Answer: No. Copper is less reactive than zinc, so it cannot displace zinc from its compound.

8.An iron nail is left in blue copper(II) sulfate solution. Describe two observations and write the balanced equation.

Answer: A pink-brown coating of copper forms on the nail, and the blue colour of the solution fades (becoming pale green as iron(II) sulfate forms). Fe + CuSO₄ → FeSO₄ + Cu

9.Which pair would react?
  1. ASilver + copper(II) nitrate solution
  2. BCopper + magnesium sulfate solution
  3. CMagnesium + iron(II) sulfate solution
  4. DIron + zinc chloride solution

Answer: Magnesium + iron(II) sulfate solution

Magnesium is above iron in the series, so it displaces iron. In each of the other pairs the free metal is less reactive than the metal in the compound.

Part C: Interpreting results

Four metals, W, X, Y and Z, were each placed in solutions of the others' salts (✓ = reaction, ✗ = no reaction).

Metal W: with salt of X ✗, salt of Y ✓, salt of Z ✗ · Metal X: with salt of W ✓, salt of Y ✓, salt of Z ✗ · Metal Y: with salt of W ✗, salt of X ✗, salt of Z ✗ · Metal Z: with salt of W ✓, salt of X ✓, salt of Y ✓

10.Use the results to write metals W, X, Y and Z in order from most to least reactive.

Answer: Z, X, W, Y

  1. Z displaces all three others, so it is most reactive
  2. X displaces W and Y
  3. W displaces only Y
  4. Y displaces none, so it is least reactive
11.Metal Y does not react with dilute acid. What does this suggest about its position compared with hydrogen?

Answer: Metal Y is below hydrogen in the reactivity series.

Part D: Extracting metals

12.Iron is extracted by heating iron(III) oxide with carbon. Balance: Fe₂O₃ + C → Fe + CO₂

Answer: 2Fe₂O₃ + 3C → 4Fe + 3CO₂

  1. Left: Fe 4, O 6, C 3
  2. Right: Fe 4, C 3, O 6 (balanced)
13.In the thermite reaction, aluminium powder reacts with iron(III) oxide, producing molten iron. Balance: Al + Fe₂O₃ → Al₂O₃ + Fe, and explain why the reaction happens.

Answer: 2Al + Fe₂O₃ → Al₂O₃ + 2Fe. Aluminium is more reactive than iron, so it displaces iron from iron(III) oxide.

  1. Left: Al 2, Fe 2, O 3
  2. Right: Al 2, O 3, Fe 2 (balanced)
14.A copper ore contains 0.5% copper by mass. What mass of copper could be obtained from 2000 kg of ore?

Answer: 10 kg

  1. 0.5% of 2000 = 0.005 × 2000
  2. = 10 kg
15.Aluminium is more abundant in Earth's crust than iron, yet it was not produced in large amounts until the late 1800s, long after iron. Use the reactivity series to explain why, and explain why carbon can be used to extract iron but not aluminium.[4 marks]

Model answer: Aluminium is above carbon in the reactivity series, so carbon is not reactive enough to remove oxygen from aluminium oxide (it cannot displace aluminium). Aluminium must instead be extracted by electrolysis of molten aluminium oxide, which needs a very large amount of electrical energy, and this was not possible on a large scale until electricity generation developed in the late 1800s. Iron is below carbon, so heating iron oxide with carbon (charcoal or coke) displaces the iron. This simple method has been used for thousands of years.

Success criteria:

  • Aluminium is above carbon, iron is below carbon
  • Carbon can displace iron from its oxide but not aluminium
  • Aluminium needs electrolysis
  • Links the late discovery to the need for electricity
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