On the formal potential of the cerium(IV)–cerium(III) couple at –5 °C in 6.5 mol kg–1 HClO4

Abstract

In order to establish the formal potential E^f of the Ce^IV–Ce^III couple, the e.m.f. of the cell (i) has been studied at –5 °C as a function of the concentrations of both Ce^III and Ce^IV. The [graphic omitted] comprehensive set of redox potential data, at concentrations of Ce^III and Ce^IV ranging from 0.01 to 0.1 and from 0.001 to 0.125 mol kg^–1 respectively, have been explained according to the equilibrium: 2Ce^IV⇌[Ce^IV]₂. From these data, both the equilibrium constant, K_D= 15 ± 2 kg mol^–1, and the limiting value, as the cerium(IV) concentration approaches zero, of the formal redox potential, E^f(l= 6.5 mol kg^–1, –5 °C)= 1 755 ± 2 mV, against the molal hydrogen electrode at –5 °C, have been calculated. Additional experimental data, gathered in order to find the correct chemical formulae of both the monomeric and the dimeric species, are also discussed.