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 Ef of the CeIV–CeIII couple, the e.m.f. of the cell (i) has been studied at –5 °C as a function of the concentrations of both CeIII and CeIV. The [graphic omitted] comprehensive set of redox potential data, at concentrations of CeIII and CeIV 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: 2CeIV⇌[CeIV]2. From these data, both the equilibrium constant, KD= 15 ± 2 kg mol–1, and the limiting value, as the cerium(IV) concentration approaches zero, of the formal redox potential, Ef(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.