Partial molar volumes of some salts in aqueous solutions
1957; Elsevier BV; Volume: 12; Issue: 1-2 Linguagem: Inglês
10.1016/0016-7037(57)90022-4
ISSN1872-9533
Autores Tópico(s)Phase Equilibria and Thermodynamics
ResumoA considerable body of information exists on the densities of aqueous solutions of simple electrolytes at different temperatures. From these data the partial molar volumes of these salts in solution have been computed as functions of concentration and temperature. Knowledge of these volumes has further enabled a calculation of the partial molar volumes of water in the corresponding solutions through the use of the Gibbs-Duhem equation. Many difficulties arise as one attempts to extrapolate the volume data to infinite dilution. One common problem is the lack of sufficiently accurate density data at low concentrations. Another major difficulty is the lack of a reliable theory of electrolytic solutions at high concentrations; for the Debye-Hückel theory is valid only for very dilute solutions and cannot be used in many cases of geologic interest. It is found that at low concentrations the partial molar volumes of the ions are approximately additive. These “ionic partial molar volumes” are tabulated; from these the partial molar volumes of salts for which no direct data exist may be estimated. The additive relation is best obeyed by univalent salts and becomes progressively less satisfactory as the ionic charges increase. The partial molar volumes of most of the studied salts are less than their molar volumes in the solid state; and so their pressure coefficients of solubility are positive. Such information is useful in many geochemical problems. Some possible applications are suggested and summarized and examples given.
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