Home / iGCSE Chemistry 0620 Extended – 6.4 Redox- Exam Style Questions Paper 2

iGCSE Chemistry 0620 Extended - 6.4 Redox- Exam Style Questions Paper 2- New Syllabus

iGCSE Chemistry MCQ (Extended) Paper 2 - All Chapters

Question

The equation shows the reaction between copper and concentrated nitric acid.

\(\mathrm{Cu(s) + 4HNO_3(aq) \rightarrow Cu(NO_3)_2(aq) + 2NO_2(g) + 2H_2O(l)}\)

Which element is reduced in this reaction?

A. oxygen
B. nitrogen
C. copper
D. hydrogen

▶️ Answer/Explanation
Oxidation numbers: In \(\mathrm{HNO_3}\), N has oxidation number +5. In \(\mathrm{NO_2}\), N has oxidation number +4. A decrease in oxidation number indicates reduction. Therefore, nitrogen is reduced. Copper is oxidised (0 → +2). Oxygen and hydrogen do not change oxidation state.
✅ Answer: (B)

Question

The equation for the reaction between aluminium and iron(III) oxide is shown.

\[2\mathrm{Al} + \mathrm{Fe_2O_3} \rightarrow \mathrm{Al_2O_3} + 2\mathrm{Fe}\]

Which statement about this reaction is correct?

A. The aluminium acts as an oxidising agent.
B. It shows that iron is more reactive than aluminium.
C. The oxidation number of the aluminium decreases during the reaction.
D. It shows that aluminium has a greater tendency to form ions than iron.

▶️ Answer/Explanation

Correct Answer: D

Explanation: In this thermite reaction, aluminium displaces iron from iron(III) oxide because aluminium is more reactive than iron. Aluminium loses electrons (oxidation: Al → Al³⁺ + 3e⁻) and acts as a reducing agent. The displacement shows that aluminium has a greater tendency to form positive ions than iron.

✅ It shows that aluminium has a greater tendency to form ions than iron.

Question

What is the oxidation number of chromium in the \(\mathrm{Cr_2O_7^{2-}}\) ion?

A. -2
B. -1
C. +6
D. +12

▶️ Answer/Explanation
Oxygen has an oxidation number of -2. The sum of the oxidation numbers in the ion equals its charge (-2). Let the oxidation state of Cr be \(x\): \(2x + 7(-2) = -2 \Rightarrow 2x – 14 = -2 \Rightarrow 2x = 12 \Rightarrow x = +6\).
✅ Answer: (C)
More iGCSE Chemistry Paper 2 Questions.............
Scroll to Top