Master's Theses

Department

Chemistry

Degree Name

Master of Science (MS)

Abstract

The specific problem of this thesis was to determine the stability constants of methylglyoxal bis-(guanylhydrazone) chelates with Co(II), Cd(II), Ni(II), Zn(II), Cu(II), and Cr(III) ions. This investigation was made at 25°C., 50°C., and 75°C., by polarographic and spectrophotometric methods. Values of the thermodynamic functions--AG, AH, AS--were calculated from the stability constants. Previous research has shown that the stoichiometry of the chelate formation is 1:1. This was considered a valid fact and the stability constants were calculated on the basis of 1:1 stoichiometry. (i) Polarographic Determinations: Reduction waves were obtained at 25°C., 50°C., and 75°C. for Co(ll), Cu(II), Cd(II), Ni(II), Zn(ll), and Cr(lll ) perchlorates and their chelates. A study was made to determine the Influence of pH variation on half-wave potentials of these simple metal ions and their chelates. Sodium hydroxide and perchloric acid were used to obtain the desired pH. Optimum pH was found to be between three and four for all systems studied. Saturated sodium tartrate-tartaric acid buffer (pH 3.5) was used to maintain the pH within this range. In obtaining the reduction waves Triton X- 100 was used as a maximum suppressor and sodium perchlorate was used as the electrolyte. The change in half-wave potentials between a simple metal ion and its chelate is directly related to the stability constant. (ii) Spectrophotometric Determinations: Absorbancies of a series of standard solutions of Co(II), Cu(II), Cd(II), Ni(II), Zn (ll), and Cd(ll) perchlorates and methylglyoxal bis-(guanylhydrazone) were obtained and plots were made of concentration versus absorbance for these systems at the wave lengths of maximum absorptivity. Molar absorptivities for metal ions and for methylglyoxal bis-(guanylhydrazone) were calculated. After mixing known amounts of metal ion and methylglyoxal bis-(guanylhydrazone), the equilibrium concentrations of each were determined from comparisons of absorbancies to the standard plots. From these concentrations the stability constants were calculated. Temperatures of the samples were controlled by introducing a special cell holder through which a constant temperature liquid was circulated.

Keywords

Perchlorates, Chelates, Polarography, Spectrophotometric, Absorbance scale (Spectroscopy), Hydrogen-ion concentration

Advisor

Dr. Max Rumpel

Date of Award

Summer 1967

Document Type

Thesis - campus only access

Rights

© The Author(s)

Comments

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