Abstract
The molal acid association quotients of tris(hydroxymethyl)aminomethane (Tris, also abbreviated as THAM) were determined potentiometrically in a concentration cell fitted with hydrogen electrodes. The emf was recorded for equimolal Tris/Tris-HCl buffer solutions from 5 to 200°C at approximately 25° intervals, and at ionic strengths of 0.0759, 0.2012, 0.7232, 1.9996, 3.5077, and 4.9599. The molal association quotients, as well as those selected from the literature and calorimetrically-determined enthalpies of reaction, were simply described by a six parameter equation which yielded the following thermodynamic quantities at infinite dilution and 25°C: logK=8.071±0.009, ΔH° = -47.53 ± 0.13 kJ-mol-1, ΔS° = -4.9 ± 0.5 J-K-1-mol-1, and ΔC °p = 67 ± 13 J-K-1-mol-1. The fitting equation for this isocoulombic reaction incorporates a four term expression for log K and a linear isothermal dependence on ionic strength.
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Palmer, D.A., Wesolowski, D. Acid association quotients of tris(hydroxymethyl)aminomethane in aqueous NaCl media to 200°C. J Solution Chem 16, 571–581 (1987). https://doi.org/10.1007/BF00646335
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DOI: https://doi.org/10.1007/BF00646335