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2017 O Level Chem P1 Q17 — Redox / Oxidation State Changes Solution

Redox / Oxidation State Changes 2017 O Level Pure Chemistry · Paper 1 · Q17

Question

In which equations is manganese being reduced? 1 2Mn(OH)₂ + H₂O₂ → Mn₂O₃ + 3H₂O 2 MnO₂ + 4HCl → MnCl₂ + Cl₂ + 2H₂O 3 MnO₄⁻ + 8H⁺ + 5Fe²⁺ → 5Fe³⁺ + Mn²⁺ + 4H₂O

A1, 2 and 3
B1 and 2 only
C2 and 3 only
D3 only

Correct answer: C

Video Solution

Explanation

Answer: C. Reduction is a decrease in oxidation state. In equation 1 manganese goes from +2 in \(\text{Mn(OH)}_2\) to +3 in \(\text{Mn}_2\text{O}_3\), so it is oxidised.

In equation 2 it goes from +4 in \(\text{MnO}_2\) to +2 in \(\text{MnCl}_2\) (reduced), and in equation 3 it goes from +7 in \(\text{MnO}_4^{-}\) to +2 in \(\text{Mn}^{2+}\) (reduced). So manganese is reduced in 2 and 3 only.

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