On Mn(Hg)/Mn(II) equilibria and reactions in aqueous solution

The title subject has been studied through galvanostatic single-pulse and chronopotentiometric measurements on the Mn(Hg)/Mn(II) electrode and equilibrium measurements on the same and the Ag/AgCl electrode, all in x MMnCl₂+(0.5?x)M MgCl₂ solutions of pH 4.3–4.9 at 25°C. The Mn(Hg)/Mn(II) reactions are found to occur in two consecutive steps, an unsymmetric (α_c near 0.8) ion-transfer step Mn(Hg)/Mn(I) and an essentially symmetric (α_c near 0.5) electron-transfer step Mn(I)/Mn(II). Besides charge transfer, no sluggishness other than diffusion is observed, but the dispersed precipitate Mn₂Hg₅ of saturated amalgam serves as an ageing-dependent source of anodic reactant Mn(Hg). Quantitative kinetic and thermodynamic data are presented and discussed. Comparisons are made to corresponding reactions for the succeeding elements iron, cobalt, nickel, copper, and zinc.