AQA A-Level Chemistry Paper 3, 2023: Question 24

1 mark · Easy difficulty · Multiple Choice

Decolourisation of Potassium Manganate(VII) This question tests the ability to identify a compound that can reduce acidified potassium manganate(VII), causing it to decolourise. It focuses on recognising reducing agents among the given compounds.

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Question

AQA A-Level Chemistry Paper 3, 2023: Question 24
Question text

24 Which compound can decolourise acidified potassium manganate(VII) solution?

[1 mark]

A AgNO3

B CuSO4

C FeSO4

D Fe2(SO4)3

Mark scheme

Show the mark scheme Mark scheme for AQA A-Level Chemistry Paper 3, 2023: Question 24

24 C 1 (AO1) FeSO4

How to answer it

Understanding Decolourisation of Acidified Potassium Manganate(VII)

Question

Which compound can decolourise acidified potassium manganate(VII) solution?

  • A: AgNO3
  • B: CuSO4
  • C: FeSO4
  • D: Fe2(SO4)3

Correct Answer: C

The correct answer is FeSO4 . Ferrous sulfate (FeSO4) contains Fe2+, which can act as a reducing agent, oxidising to Fe3+ and reducing MnO4- to Mn2+, thereby decolourising the solution.

Explanation

  • Acidified potassium manganate(VII) (MnO4-) is a strong oxidising agent. It is reduced to Mn2+, which is colourless.
  • Fe2+ in FeSO4 acts as the reducing agent, being oxidised to Fe3+.

Balanced ionic equation:

5Fe2+ + MnO4- + 8H+ → 5Fe3+ + Mn2+ + 4H2O

Why Other Options Are Incorrect

  • A: AgNO3 – Silver nitrate is not a reducing agent and cannot reduce MnO4-.
  • B: CuSO4 – Copper(II) sulfate contains Cu2+, which is not a reducing agent.
  • D: Fe2(SO4)3 – This contains Fe3+, which is already in an oxidised state and cannot act as a reducing agent.

Teacher Tip

Tip: Focus on the oxidation states of transition metals. MnO4- is a classic test for reducing agents, as it changes from purple to colourless when reduced to Mn2+.

Final Answer

The correct choice is:

C: FeSO4

Topics

Inorganic Chemistry · 3.2.5 Transition Metals

Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.