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Lookup NU author(s): Emeritus Professor Arthur Covington
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Equations were determined for calculation of stoichiometric (molality scale) dissociation constants Km of acetic acid in buffer solutions containing acetic acid, sodium acetate, and sodium chloride from determined thermodynamic dissociation constants Ka of this acid at temperatures from (0 to 60) °C, and molalities of components in solution. These equations were based on single-ion activity coefficients obtained by Hũckel-type equations. The thermodynamic dissociation constants and acetate parameters required were determined from the Harned cell data of Harned and Ehlers. The interaction parameter between neutral acetic acid molecules and acetate ions was determined from Harned cell data for unbuffered aqueous mixtures of acetic acid and NaCl at 25 °C, and the resulting value applied to all temperatures. The interaction parameters between hydrogen ions and chloride ions were taken from the recent data reassessment by Partanen and Covington. The parameters resulted from interactions between hydrogen ions and sodium ions and between sodium and chloride ions were determined from the Harned cell data measured by Harned for aqueous mixtures of HCl and NaCl. The resulting equations were tested with literature data for cells both with and without a liquid junction at various temperatures. The new equations predict well the literature data used in the tests. The new parametric equations were used to check the pH values of 0.01 molal acetate and 0.1 molal acetate buffers recommended by IUPAC for temperatures from (0 to 60) °C, and agreement was usually found to be within ±0.005. Calculated p(mH) values are also tabulated for buffer solutions containing NaCl as the major component and acetate species as minor components for calibration glass electrode cells for direct measurement, particularly in potentiometric titrimetry, of hydrogen ion molality.
Author(s): Partanen JI, Covington AK
Publication type: Article
Publication status: Published
Journal: Journal of Chemical and Engineering Data
Year: 2003
Volume: 48
Issue: 4
Pages: 797-807
ISSN (print): 0021-9568
ISSN (electronic): 1520-5134
Publisher: American Chemical Society
URL: http://dx.doi.org/10.1021/je030100v
DOI: 10.1021/je030100v
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