The reduction of Bi(III) to Bi(Hg) at the dropping mercury electrode in 0[middle dot]5 M perchloric acid solution containing 0-0[middle dot]3 M chloride ion becomes increasingly reversible, generally speaking, as the [Cl-]/ [Bi(III)] ratio increases, as evidenced by changes in various criteria used for determining the "reversibility" of a polarographic electrode process, e.g., the magnitude of the heterogeneous rate constant of the electrochemical reaction (ke), the slope of the d.c. polarogram log plot, and the magnitude of [varrho], the a.c. polarographic efficiency (ratio of the observed and theoretical magnitudes of the faradaic alternating current). The concentration ratio is not, however, the sole determining factor; the absolute concentrations also have an effect. The log plot is apparently a quite inadequate measure of reversibility; ke, which is a determining factor in the d.c. polarographic reversibility, is probably not functionally related to the thermodynamic reversibility of the electrode process; [varrho] could be a measure of the thermodynamic reversibility of the electrochemicaI process.
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http://deepblue.lib.umich.edu/bitstream/2027.42/32416/1/0000495.pdf