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2018 O Level Chem P1 Q20 — Redox / Oxidation and Reduction Solution

Redox / Oxidation and Reduction 2018 O Level Pure Chemistry · Paper 1 · Q20

Question

In which reactions is reduction taking place? 1 the conversion of nitrogen to ammonia in the Haber process 2 the formation of iron from haematite in the blast furnace 3 a reaction of acidified potassium manganate(VII) in which the colour changes from purple to colourless

A1, 2 and 3
B1 and 2 only
C1 and 3 only
D2 and 3 only

Correct answer: A

Video Solution

Explanation

Answer: A (1, 2 and 3). Reduction is gain of electrons, gain of hydrogen or loss of oxygen (a decrease in oxidation state).

1) \(\text{N}_2 \rightarrow \text{NH}_3\) (Haber process): nitrogen goes from 0 to \(-3\) and gains hydrogen, so it is reduced. 2) \(\text{Fe}_2\text{O}_3 \rightarrow \text{Fe}\) (blast furnace): iron goes from \(+3\) to 0 and loses oxygen, so it is reduced. 3) Acidified \(\text{KMnO}_4\) turning from purple to colourless: manganese goes from \(+7\) to \(+2\), so it is reduced.

All three involve reduction. Answer A.

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