434. Reactivity of anions towards electron transfer in the bismuth ? tervalent bismuth exchange reaction

Abstract

The pseudo-capacity and over-all polarisation resistance during the electroreduction of tervalent bismuth at a dropping-mercury cathode in various media were traced as a series combination; and the general features of the former are described. The combination corresponding to the peak values was then balanced against the equivalent of a simple model of the faradaic admittance, and in this way information was obtained from which the specific rate constant for the above exchange in each medium could be evaluated. In N-perchloric and N-hydrochloric acid, the results agreed excellently with those previously published. In N-nitric and N-sulphuric acid the constants were respectively 3.7 x 10-3 and 1.8 x 10-3 cm. sec.-l a t 26" f 0.5". In mixtures of nitric and perchloric acid of constant ionic strength, the rate increased sensibly with the increase of concentration of the former. The order of reactivity towards electron transfer for the various anions is briefly discussed in the light of possible ionic interactions within the electrical double layer and in the bulk of solution.HEYROVSKY,~ using oscillographic polarography, showed the reduction of tervalent bismuth to involve three-electron transfer, and to be irreversible in media containing undeformable anions such as NO,and ClO,-, but highly reversible in complex-forming media of C1-or Br-ions. These conclusions were confirmed by Randles and Somerton,2 who, investigating the electrodic behaviour in an alternating field, computed, as a measure of the degree of reversibility, the specific rate constant for the exchange Bi =+= Bi3+ + 3e.In N-perchloric and N-hydrochloric acid the constant was-reported as 3 x lo-* and 2 1 cm. sec.-l, respectively. The reversible behaviour on open circuit of both protected and unprotected bismuth electrodes as metal-metal oxychloride electrodes in hydrochloric acid media is undoubtedly consistent with the above facts. However, the extent to which anions such as NO3and SO:-may catalyse the above exchange does not seem to have been studied before. As is well known, these anions, like ClO,-, do not become specifically adsorbed. In this investigation, using a different experimental technique, we confirmed Randles and Somerton's results, and moreover examined the reactivity of the above anions, alone or in mixtures, towards electron transfer in the above reaction. EXPERIMENTALThe technique used was essentially polarography with superimposed alternating voltage.* The capacitative and resistive components of the impedance of a mercury surface were measured

Intermolecular Interactions in Systems Containing Bi(III) – ClO−4 – H2O – Selected Amino Acids in the Aspect of Catalysis of Bi(III) Electroreduction

“…The influence of supporting electrolytes on the rate and mechanism of electroreduction of Bi(III) ions on mercury electrodes was the subject of many studies 4–9. Special focus was on complexing media, such as halide, nitrate and sulfates 4–9, because of the increased rate of reversibility of Bi(III) electroreduction in those media.…”

The Catalysis of the Reduction of BiIII Ions by Methionine

“…The addition of either SO 2¹ 4 ions [13] or NO ¹ 3 ions [14] to the perchlorate supporting electrolyte also accelerates the reduction process of Bi III , although to a lesser extent than Cl ¹ ions. The order of the activity of those ions is [13]:…”

Measurements and Modeling To Determine the Reduction Potential of Uncomplexed Bi(III) in Nitrate Solutions for Application in Bi(III)-Ligand Equilibria Studies by Voltammetry

“…In this case it is that the reduction of metal ions of oxidation state three is not reversible in "non-complexing" media such as perchlorate at moderate ionic strengths (around 1 M) and this also pertains to Bi(III). [30][31][32][33] It was shown that the rate of electron transfer for Bi(III) reduction in highly acidic solutions increased with the addition of the following anions in solution: ClO 4  < NO 3  < Cl  . 31 Interestingly, at very high HClO 4 concentrations (8 M) the reduction of Bi(III) becomes fully reversible, 34 as well as in solutions of 1 M HClO 4 + 7 M NaClO 4 when using DC polarography.…”

“…[30][31][32][33] It was shown that the rate of electron transfer for Bi(III) reduction in highly acidic solutions increased with the addition of the following anions in solution: ClO 4  < NO 3  < Cl  . 31 Interestingly, at very high HClO 4 concentrations (8 M) the reduction of Bi(III) becomes fully reversible, 34 as well as in solutions of 1 M HClO 4 + 7 M NaClO 4 when using DC polarography. 35 When solutions of 1 M HClO 4 with varying concentrations of NaClO 4 (1 to 8 M) were studied it was clear that the half-wave potential was dependant on ionic strength.…”

“…35,36 At moderate ionic strengths, it was reported that the Bi(III) reduction was found to be fully reversible when chloride was added, but that it never reached full reversibility in a nitrate medium. [30][31][32][33] When determining formation constants by polarography, the relationship employed (Eq. 1) is only valid for reversible reduction potentials.…”