Electrode processes of bismuth in weakly acidic, neutral and alkaline solutions

The electrode process Bi(III)+ 3e = Bi(Hg) has been investigated in weakly acidic, neutral and alkaline solutions by means of amalgam polarography and cyclic voltammetry and chronopotentiometry with the use of hanging amalgam drop electrode. It has been found that in weakly acidic and neutral solutions, oxidation of bismuth amalgam goes through aquocomplexes of bismuth. In the cathodic step on cyclic voltammetry curves four peaks of reduction are observed, with magnitude and shape strongly dependent on pH of the solution. These peaks have been ascribed to the reduction of Bi3+, Bi(OH)+2, Bi(OH)+2 and Bi(OH)3. In alkaline solutions, oxidation of bismuth amalgam leads to Bi(OH)3. In cathodic scan on cyclic voltammetry curves only one peak is observed, which corresponds to Bi(OH)3 reduction. Formal potentials of electrode process and solubility product of Bi(OH)3 have been calculated and discussed. The step-wise nature of the overall electrode reaction has been ascertained and discussed. At higher concentrations of OH− ions, Bi(OH)3 dissolves.