Equations for the Calculation of the pH of Buffer Solutions Containing Potassium Hydrogen Phthalate, Dipotassium Phthalate, and Potassium Chloride at 298.15 K

Abstract

Published experimental thermodynamic data at 298.15 K for aqueous mixtures of H2Ph, KHPh, and KCl, of KHPh, K2Ph, and KCl, and of KHPh and KCl, where H2Ph means phthalic acid, KHPh potassium hydrogen phthalate, and K2Ph dipotassium phthalate, were used to test the methods for calculation of the pH values of phthalate buffer solutions. Equations for ionic activity coefficients are used in these methods. It is shown that all data used, up to an ionic strength of about 0.5 mol kg-1, can be predicted almost within experimental error by two methods. In one of these methods, equations of the modified Guggenheim type are used for ionic activity coefficients, and in the other equations of the Pitzer type are used. Several sets of phthalate buffer solutions are suggested in the pH range 3.8−5.3, e.g., for calibration solutions for glass electrode cells or for constant-pH reaction media where the pH is known. In the recommended sets, the pH values of the buffer solutions have been calculated by the Guggenheim method, and the pH predictions of the Pitzer method agree with those in most cases within 0.01 at least up to ionic strengths of about 0.15 mol kg-1. The recommended pH = 4.005 of the standard reference solution (0.05 mol kg-1 KHPh solution) agrees closely with the value suggested in the present study (4.003) for this solution.

Determination of the second stoichiometric dissociation constants of glycine in aqueous sodium or potassium chloride solutions at 298.15 K

“…b The second stoichiometric dissociation constant of glycine calculated by eq. [4] with the value of K a2 = 1.65 × 10 -10 and with the recommended activity parameters. Abbreviation "recd" means recommended.…”

“…The predicted cpd was calculated by eqs. [4], [8], [9], [12], and [14] using the thermodynamic value of 1.65 × 10 -10 for the second dissociation constant, the recommended activity parameters, and the glass electrode parameters k and E 0 shown in Tables 5 and 6. Symbols of the different sets are shown in the graphs.…”

“…The K m2 values were calculated by using eq. [4] with the recommended value of K a2 = 1.65 × 10 -10 and with the recommended parameter values shown in Table 3.…”

“…In this manuscript, we continue the studies (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) dealing with the thermodynamics of weak acid solutions. The purpose of these studies is to determine the stoichiometric dissociation constants (for example, the molality scale dissociation constants, K m ) for salt solutions of different weak acids, as reliably as possible from potentiometric titration data measured with glass electrodes.…”

Determination of Stoichiometric Dissociation Constants of Glycolic Acid in Dilute Aqueous Sodium or Potassium Chloride Solutions at 298.15 K

“…In this study, we continue the studies [1][2][3][4][5][6][7][8][9][10][11] dealing with the thermodynamics of weak acid solutions. The purpose of these studies is to determine the stoichiometric dissociation constants (for example the molality scale dissociation constants, K m ) for solutions of different weak acids as reliably as possible from potentiometric titration data and, additionally, from literature data obtained by galvanic cells without liquid junctions.…”