Single-ion activities and Zn/Zn(II) reactions in alkali chloride solutions

The title subject has been studied through equilibrium potential measurements on the Zn/Zn(II) and the Ag/AgCl electrode vs. SCE and galvanostatic single-step and chronopotentiometric polarization measurements on the former electrode, all in acidified (to pH about 3) solutions of 0.005 M ZnCl₂+0.99 M MeCl (for Me=Li, Na, K, and Cs) at 25°C. It is found that the Zn(II) activity decreases together with the alkali-ion activity along the sequence LiCl>NaCl>KCl>CsCl, that the chloride-ion activity essentially is insensitive to mutual substitutions of alkali ions, and that the Zn/Zn(II) reactions exhibit no other than pure activity effects of such substitutions. The results support that the Zn/Zn(II) electrode reacts in two consecutive steps with Zn(I) as intermediate, and that some sluggishness appears in chemical reactions to and from electroactive Zn(II) species.