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CAIE IGCSE Chemistry Oxidising and Reducing Agents

Practise identifying oxidising and reducing agents from electron transfer, oxidation-state changes or diagnostic redox reagent observations.

Syllabus
2026–2028
Course
Chemistry 0620

Exam points

  • identify the oxidising agent as the electron acceptor that is itself reduced
  • identify the reducing agent as the electron donor that is itself oxidised
  • use ionic equations, oxidation numbers or reagent colour changes to justify each choice

6.4.13—Oxidising agents and reducing agents question 1

[Maximum number: 2]

Displacement reactions occur between metals and metal ions.
Displacement reactions can be used to determine the order of reactivity of metals such as lead (Pb), nickel (Ni), and silver (Ag).

The ionic equation for a displacement reaction is shown.

Ni( s)+Pb2+(aq)→Pb( s)+Ni2+(aq)\mathrm{Ni}(\mathrm{~s})+\mathrm{Pb}^{2+}(\mathrm{aq}) \rightarrow \mathrm{Pb}(\mathrm{~s})+\mathrm{Ni}^{2+}(\mathrm{aq})

The ionic half-equations for this reaction are shown.

Ni( s)→Ni2+(aq)+2e−Pb2+(aq)+2e−→Pb( s)\begin{gathered} \mathrm{Ni}(\mathrm{~s}) \rightarrow \mathrm{Ni}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \\ \mathrm{Pb}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \rightarrow \mathrm{Pb}(\mathrm{~s}) \end{gathered}

The ionic half-equations show that electrons are donated by nickel atoms and accepted by lead ions.

Identify the reducing agent in the displacement reaction. Give a reason for your answer.
reducing agent
reason

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