"The standard electrode potentials of a phosphinic-acid ion-exchange re" by Guillermo Francisco Torres Andrade
 

Masters Theses

Date of Award

8-1988

Degree Type

Thesis

Degree Name

Master of Science

Major

Chemistry

Major Professor

George K. Schweitzer

Committee Members

D.C. Kleinfelter

Abstract

The oxidation-reduction characteristics of a bifunctional phosphinic acid resin and its model compound, phenylphosphinic acid, were investigated using a series of cationic species. The cations selected were Hg(II), Bi(III), Fe(III), Pb(II), Ni(II), Co(II), andCu(II). Other species, such as AuCl4- and PtCl4-2 were also investigated. Solutions of these species with concentrations ranging between 10-1M and 10-4M were mixed with portions of resin (0.2 g.-0.5 g) and the course of the reaction was followed by visual observation. Similarly, solutions of the model compound at concentrations of 10-1M to 10-4M were allowed to react with the indicated metal ion solutions at equal volumes, the course of these reactions also being followed by visual observation. Both the phosphinic acid resin and the model compound were found to reduce metal ion species having positive standard electrode potentials but were relatively inert for species with negative standard electrode potentials. An exception to this general rule was observed for Bi(III) and Fe(III) ions, which did not oxidize the resin and tended to form insoluble compounds with the phenylphosphinic acid. The reductions of cationic species occurred at different rates, and no significant differences were observed by variations in the pH of the analyte solutions between 0.50 and 4.02 pH units. Of particular importance in the IV experiments were (1) the study of the kinetics of the reaction between the model compound and the Cu{II) solutions and (2) the determination of the thermodynamic equilibrium of the reaction which was quantitatively observed at 60°C, 75°C, and 90°C. Experimental measurements of pH values and the determination of metal concentrations by atomic absorption and potentiometry were used to provide data for calculation of the equilibrium constants for the reactions. By using fundamental thermodynamic relationships among the free energy change,the reaction enthalpy, the equilibrium constant, and the electrode potential, it was possible to estimate the standard electrode potential for the oxidation of the model compound, which is deemed to be approximately equal to that of the redox resin.

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