28.2.8—Predict, using E

Write the relevant reduction half-equations, select the more positive reduction as the cathode, and calculate E°cell = E°cathode − E°anode. A positive value supports the written standard direction.

Transition-metal ions can act as oxidising or reducing agents depending on their pair and oxidation state. Balance electrons after choosing the direction.

If MnO₄⁻/Mn²⁺ is more positive than Fe³⁺/Fe²⁺ in acid, permanganate can oxidise Fe²⁺ to Fe³⁺ while being reduced.

Do not rank ions without specifying the half-equations or assume a reaction is feasible under non-standard concentrations from E° alone.