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CAIE A-Level Chemistry 24.2.3 Measuring Standard Electrode Potentials

Practise drawing cells used to measure metal, non-metal and same-element redox-couple potentials against the SHE.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • use the reacting metal as electrode for M^n+/M, or inert Pt for ion/ion and non-metal couples
  • include both solutions, gas delivery where needed, salt bridge, wires and a high-resistance voltmeter
  • apply standard concentration, gas pressure and temperature before reporting E° relative to the SHE

24.2.3—Measuring standard electrode potentials question 1

[Maximum number: 3]

Hypophosphorous acid is an inorganic acid.
The conjugate base of hypophosphorous acid is H2PO2−\mathrm{H}_{2} \mathrm{PO}_{2}^{-}.

H2PO2−\mathrm{H}_{2} \mathrm{PO}_{2}^{-}is a strong reducing agent. It can be used to reduce metal cations without the need for electrolysis.
equation 1HPO32−+2H2O+2e−⇌H2PO2−+3OH−1 \quad \mathrm{HPO}_{3}^{2-}+2 \mathrm{H}_{2} \mathrm{O}+2 \mathrm{e}^{-} \rightleftharpoons \mathrm{H}_{2} \mathrm{PO}_{2}^{-}+3 \mathrm{OH}^{-}E⊖=−1.57 VE^{\ominus}=-1.57 \mathrm{~V}

Complete the diagram in Fig. 2.1 to show how the standard electrode potential of the Cr3+/Cr\mathrm{Cr}^{3+} / \mathrm{Cr} half-cell can be measured relative to that of the standard hydrogen electrode.

Identify the chemicals, conditions and relevant pieces of apparatus.

Fig. 2.1

Fig. 2.1

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