Volumetric Properties of Electrolytes in Natural Waters

The research of this dissertation has focused on the volumetric properties of electrolyte solutions, including seawater, across wide ranges of temperature and concentration. The volume and compressibility are inherently useful as physical chemical properties of electrolyte solutions. They are directly related to the density and sound speed of a solution; thus, they are important for studying physical processes and properties in the ocean, including mixing, sound transmission, and water mass stability. Possibly of greater significance, however, is the volume’s role as a thermodynamic variable that guides chemical systems into equilibrium. By analyzing the volume properties of electrolyte solutions over wide ranges of temperature and concentration, the results of this dissertation can be used to study the physical chemistry of the ocean, from the surface to depth, geothermal waters, estuaries, rivers, and industrially treated waters. In the first part of my thesis work, I have examined the volume properties of electrolytes, including seawater and rare earth elements from measurements of the density and sound speed. Using the volume parameters, I evaluated two different chemical computational models to estimate the density and compressibility of mixed solute solutions on a composition basis over a wide range of temperature and concentration. The results have applicability for examining brines to fresh waters, and can be used in industrial applications of seawater, such as desalination and other chemical engineering treatments. In the second part of my dissertation, I make use of the volume as a thermodynamic variable to estimate the effect of pressure on a chemical equilibrium reaction. The partial molal volume (V) is the pressure partial derivative of the Gibb’s Free Energy (G) and it can be used to examine various equilibrium reactions, including ion association, acid dissociation, and mineral solubility. I have examined the volume change for the dissociation of a Tris buffer, to predict the effect of pressure on its dissociation. The Tris buffer is used in ocean studies to calibrate electrodes and indicators for measuring the pH of ocean waters, and knowledge of the effect of pressure on the buffer’s dissociation reaction will be useful for the in-situ calibration of pH sensors. The results of this dissertation can contribute to: 1) defining the thermodynamic state variables of various electrolyte solutions, including seawater, rare earth elements, and the Tris buffer with volume and compressibility measurements; 2) enabling the prediction of physical chemical properties of mixed-solute solutions of varying composition; and 3) enabling the prediction of the effect of pressure on chemical equilibria