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Type of Document	Dissertation
Author	Foster, James Norman
URN	etd-04092003-115642
Persistent URL	http://resolver.caltech.edu/CaltechETD:etd-04092003-115642
Title	The electrochemistry of certain metal cations in pyrophosphate media. A theoretical study of chronopotentiometry and chronoamperometry at unshielded electrodes. Determination of cobalt by constant current coulometry
Degree	PhD
Option	Chemistry
Advisory Committee	Advisor Name Title Unknown Committee Member
Keywords	None
Date of Defense	1964-12-17
Availability	unrestricted
Abstract NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. In Part I results are reported for the electrolytical reduction of iron(III), copper(II), lead(II), zinc(II), and cadmium(II) in sodium pyrophosphate media. In the cases of iron(III) and copper(II), reduction in neutral and basic pyrophosphate media is irreversible. However, if a pyrophosphate ligand is dissociated from the metal complex, a species is obtained that is reversibly reduced. In the case of iron(III) in the region 4 < pH < 6, loss of a hydrogen pyrophosphate ligand results in a species that is reversibly reduced. The dissociation constant is 2.8 x 10[superscript -3], the rate constant for dissociation of the ligand is 24 sec.[superscript -1], and the rate constant for association is 8.5 x 10[superscript 3] M[superscript -1]sec.[superscript -1]. In the case of copper(II) the loss of a sodium pyrophosphate ligand yields a species that is reversibly reduced. The dissociation constant is 3.2 x 10[superscript -3], the rate constant for dissociation of the ligand is 19 sec.[superscript -1], and the rate constant for association is 5.9 x 10 [superscript 3] M[superscript -1]sec.[superscript -1]. These constants were determined by chronopotentiometry. The reduction of zinc(II) is irreversible in neutral pyrophosphate media; however, this irreversibility is not due to a slow chemical reaction. The reduction of lead(II) is not reversible in neutral pyrophosphate media, but this reduction is not sufficiently irreversible to allow the mechanism of the reduction to be studied by polarography or chronopotentiometry. Reduction of cadmium(II) was studied by polarography, but no quantitative results were obtained. In Part II equations for the product [...] and the product [...] are derived for the cases of chronopotentiometry and chronoamperometry, respectively, at an unshielded electrode. The equations for an annular electrode or radius r are [...] For a rectangular electrode with dimensions b and c the above equations are valid if the quantity bc/(b+c) is substituted for the variable r. In Part III a method is described by which cobalt may be determined with a relative error of less than 0.1%. In this method triscarbonatocobaltate(III) oxidizes iodide to iodine. Arsenic(III) is added to reduce the iodine and coulometrically generated iodine is employed to titrate excess arsenic(III).
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