Electrode processes at mercury in the far cathodic potential region I. The reduction of K+ and Na+ in neutral aqueous media

Abstract

The reduction of K+ and Na+ ions at the dropping mercury electrode in 1 M aqueous solutions of halide salts has been studied using d.c. polarography and electrode impedance measurements as a function of frequency and electrode potential. The results confirm that the reductions are reversible but that the primary reduction process is accompanied by an irreversible secondary process which seems likely to be reduction of water. The influence of this process on the analysis of the K+ wave is discussed. The implications of the observation of a coupled process are more generally discussed. In particular, it is concluded that potentiometric measurements of the standard potentials of alkali-amalgam/alkali ion redox couples are always in error because a mixed potential is observed instead of the Nernst potential. Two principally different correction procedures are suggested.