Joseph R. Delmastro

Influence of mercury drop growth and geometry on the A.C. polarographic wave

Theoretical reassessment of the contributions of electrode growth and geometry on the a.c. polarographic wave is given. Examination of the theory for the ‘quasi-reversible’ a.c.wave indicates that these factors contribute significantly when the d.c.process is influenced by charge transfer kinetics. Generalization of these results leads to the conclusion that growth and geometry can be important when any rate process in addition to diffusion kinetically influences the d.c. process. If the d.c. process is diffusion-controlled or non-existent (zero direct current), theory predicts that these effects will be negligible, in agreement with earlier works of Koutecky and Gerischer. An equation is given for the a.c. polarographic wave with a quasi-reversible process at the expanding spherical electrode. Derivation of similar exact expressions for more complex mechanisms is discussed. Implications of these results with regard to experimental approach and work with stationary electrodes are considered.

Fundamental harmonic a.c. polarography with disproportionation following the charge transfer step: Theory and experimental results with the U(VI)/U(V) couple

Summary A theoretical and experimental study is presented for the small amplitude a.c. polarographic response with systems involving second-order disproportionation following the charge transfer step. The theoretical derivation combines wellestablished analytical procedures for solving the a.c. boundary value problem with various nummerical methods to account for effects of d.c. polarization. The resulting rate law predicts significant influences of the disproportionation step on a.c. polarographic observables, including several novel effects not predicted or observed with first-order coupled chemical reactions. The basis for kinetic assessment of rate parameters associated with the heterogeneous charge transfer step and the homogenous disproportionation mechanism is clearly indicated by the theoretical rate law. The computer programs developed on the basis of the derivation provide the means for calculating predicted responses on the basis of most commonly-used mathematical models for the DME, including the expanding sphere model. The electrode reduction of UO 2 2+ at the mercury-aqueous 6 M HClO 4 interface is used as a model for the mechanism in question in an experimental assay of the theorys fidelity. Various predicted trends are verified experimentally. Analysis of the experimental data using the theoretical rate law generated rate parameters for the heterogeneous electrode reaction, the homogeneous disproportionation step and the diffusion process. Agreement between theory and experiment obtained with this set of rate parameters is quite satisfactory for a variety of observables. Finally, the disproportionation rate constant obtained is consistent with previous measurements by a variety of authors using both electrochemical and non-electrochemical methods.

Fundamental harmonic a.c. polarography with irreversible dimerization following the charge transfer step: Theory and experimental results with the benzaldehyd system

Summary A theoretical and experimental study is presented for the small amplitude fundamental harmonic a.c. polarographic response with systems involving dimerization following the charge transfer step. The theoretical derivation invokes the procedure recently presented for the disproportionation case, which combines numerical methods with conventional functional analysis procedures. Computer programs were developed which provide the option of calculating the a.c. polarographic response on the basis of various commonly-used models for the DME, including the expanding sphere model. The electrode reduction of benzaldehyde in alkaline aqueous ethanol is employed as a model system in an experimental evaluation of the theoretical equations. Excellent agreement is obtained between predictions of the theoretical a.c. polarographic rate law and experimental results.

Alternating current polarography of electrode processes with coupled homogeneous chemical reactions: III. Theory for systems with multi-step first-order chemical reactions

Abstract The theory of a.c. polarography for systems with coupled first-order chemical reactions is extended to consider systems with multi-step chemical processes coupled with a single electrochemical step. Reaction schemes involving two-step preceding or following reactions, combined preceding and following reactions and schemes with catalytic reactions combined with preceding or following reactions are examined. Attention is focused on phase angles whose predicted behaviour is examined and discussed with regard to mechanistic distinction. Results of calculations predict that a.c. polarographic phase angle studies may often provide definite qualitative evidence of these more complicated mechanisms enabling convenient mechanism diagnosis