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CAIE IGCSE Chemistry Identifying Electron-Transfer Redox

Practise identifying redox reactions through simultaneous electron loss and gain, pairing half-equations and tracing electron flow between species.

Syllabus
2026–2028
Course
Chemistry 0620

Exam points

  • identify redox when electrons lost by one species are gained by another species
  • pair oxidation and reduction half-equations so transferred electron numbers match
  • distinguish electron-transfer redox from precipitation, acid-base or other reactions

6.4.8—Redox reactions as reactions involving question 1

[Maximum number: 1]

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.

What is the general term given to the type of reaction in which electrons are transferred from one species to another?

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