Abstract
The equilibrium quotients for the first ionization of aqueous carbon dioxide were previously determined at this laboratory. A similar potentiometric technique has now been employed to determine the second ionization quotients in NaCl media to 5m and from 50 to 250°C. The results have been combined with selected information in the literature and modeled to derive thermodynamic parameters including equilibrium constants, activity coefficient quotients, changes in enthalpies and changes in heat capacity along the saturation pressure curve. Approximate values for pressure coefficients were obtained to permit the short extrapolations from experimental conditions to the saturation pressure condition. The results demonstrate that log K2/Kw, when plotted vs. 1/T, gives nearly a straight line as has been observed for a number of other such processes. This provides the best means of extrapolation beyond the temperature of the measurements. The results have been applied to an examination of the solubility of calcite (calcium carbonate) as a function of hydrogen ion molality (in a given NaCl medium) for the condition where the calcium ion molality equals the total carbonate molality (in all forms).
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On leave from Furman University, Greenville, SC
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Patterson, C.S., Busey, R.H. & Mesmer, R.E. Second ionization of carbonic acid in NaCl media to 250°C. J Solution Chem 13, 647–661 (1984). https://doi.org/10.1007/BF00650372
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DOI: https://doi.org/10.1007/BF00650372