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CIE iGCSE Co-Ordinated Science C6.3 Redox Exam Style Questions Paper 1

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Question

Which equation shows the oxidation of a metal?

A. \(\mathrm{CuO} + \mathrm{H}_2 \rightarrow \mathrm{Cu} + \mathrm{H}_2\mathrm{O}\)
B. \(\mathrm{CuO} + \mathrm{Zn} \rightarrow \mathrm{Cu} + \mathrm{ZnO}\)
C. \(\mathrm{Fe}_2\mathrm{O}_3 + 3\mathrm{CO} \rightarrow 2\mathrm{Fe} + 3\mathrm{CO}_2\)
D. \(2\mathrm{ZnO} + \mathrm{C} \rightarrow 2\mathrm{Zn} + \mathrm{CO}_2\)

▶️ Answer/Explanation
Oxidation is defined as the gain of oxygen. In option B, zinc gains oxygen to form zinc oxide (\(\mathrm{ZnO}\)), so zinc is oxidised.
In options A, C, and D, metal oxides are being reduced (losing oxygen) to form metals.
✅ Answer: (B)

Question

The equation for the reaction between copper(II) oxide and carbon is shown.

\[2\mathrm{CuO} + \mathrm{C} \rightarrow 2\mathrm{Cu} + \mathrm{CO}_2\]

Which substance is oxidised in this reaction?

A. C
B. CO₂
C. Cu
D. CuO

▶️ Answer/Explanation
In this reaction, carbon (C) gains oxygen to form carbon dioxide (CO₂), so carbon is oxidised. Copper(II) oxide (CuO) loses oxygen to become copper (Cu), so it is reduced. Oxidation is defined as the gain of oxygen, and reduction is the loss of oxygen. Therefore, carbon is the substance that is oxidised.
✅ Answer: (A)

Question

Which statement explains why the rusting of iron is an oxidation reaction?

A. Iron gains oxygen.
B. Iron is a transition element.
C. Iron is very reactive.
D. Iron loses oxygen.

▶️ Answer/Explanation
Oxidation is defined as the gain of oxygen; during rusting, iron reacts with oxygen (and water) to form hydrated iron(III) oxide (\(\text{Fe}_2\text{O}_3 \cdot \text{H}_2\text{O}\)).
Since iron gains oxygen in this process, rusting is correctly classified as an oxidation reaction; the fact that iron is a transition element or reactive metal does not explain why the reaction is oxidation.
✅ Answer: (A)

Question

The equation for the reaction between iron(III) oxide, \(Fe_2O_3\), and carbon is shown.

\(2Fe_2O_3 + 3C \to 4Fe + 3CO_2\)

Which statement about this reaction is correct?

A. C is oxidised.
B. \(CO_2\) is reduced.
C. Fe is oxidised.
D. \(Fe_2O_3\) is oxidised.

▶️ Answer/Explanation
Carbon starts with no oxygen and ends up combined with oxygen in \(CO_2\).
Gaining oxygen means carbon has been oxidised.
Meanwhile \(Fe_2O_3\) loses oxygen to form Fe, so it is reduced, not oxidised, ruling out C and D.
✅ Answer: (A)

Question

Which reactions involve oxidation?

  1. \(\text{C} + \text{O}_2 \rightarrow \text{CO}_2\)
  2. \(2\text{NaOH} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O}\)
  3. \(2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}\)
  4. \(\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2\)

A. 1 and 3
B. 1 and 4
C. 2 and 3
D. 2 and 4

▶️ Answer/Explanation
In reaction 1, carbon gains oxygen to form \(\text{CO}_2\) — carbon is oxidised; in reaction 3, magnesium gains oxygen to form MgO — magnesium is oxidised; both are oxidation reactions.
Reaction 2 is a neutralisation (acid-base) reaction with no oxygen transfer; reaction 4 is thermal decomposition with no net gain of oxygen by any element.
✅ Answer: (A)
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