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CAIE A-Level Chemistry A2 28.2.8 Predict Using E Questions

Practise using standard electrode potentials to predict transition-metal redox feasibility and products.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • calculate E°cell from supplied reduction potentials and use its sign to judge standard-condition feasibility
  • identify which transition-metal species is oxidised or reduced and connect its oxidation state to the observation
  • balance the selected half-equations to obtain an overall ionic equation without multiplying E° values

CAIE A-Level Chemistry A2 28.2.8 Predict Using E Questions question 1

[Maximum number: 3]

[Fe(H2O)6]2+\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+} can be converted into [Fe(H2O)4(OH)2]\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}(\mathrm{OH})_{2}\right].

[Fe(H2O)4(OH)2]\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}(\mathrm{OH})_{2}\right] is a green precipitate that turns brown on standing in air.

Table 2.1 shows electrode potentials for some electrode reactions.

Table 2.1

Table 2.1

Use the information in Table 2.1 to explain why [Fe(H2O)4(OH)2]\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}(\mathrm{OH})_{2}\right] turns brown on standing in air.
Include an equation for this reaction.

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