PITZER SINGLE-ION ACTIVITY-COEFFICIENTS AND PH FOR AQUEOUS-SOLUTIONS OF POTASSIUM HYDROGEN PHTHALATE IN MIXTURES WITH KCL AND WITH NACL AT 298.15 K

Electromotive force (emf) measurements of the cell Pt-Pd\H-2\C8H5O4K(m) + MCl (m1)\AgCl\Ag, where M represents K or Na, at 298.15 K have been carried out, with the molality of potasssium hydrogen o-phthalate (C8H5O4K), m, ranging from 0.01 to 0.1 mol kg(-1), m(1)(KCl) from 0.01 to 2 mol kg(-1), and m(1)(NaCl) = 1 mol kg(-1). From emf data, pH values have been calculated for these solutions, using an approximation method based on Fitter's system for single-ion activity coefficients at high ionic strengths. Differences between these values and operational pH values obtained from conventional measurements using combination pH glass electrodes were attributed to liquid junction potential contributions. pH was constant at 3.704 +/- 0.004 when the molality of C8H5O4K was in the range 0.03-0.1 mol kg(-1) for the solutions containing 1 mol kg(-1) KCl. For 1 mol kg(-1) NaCl solutions, pH was constant at 3.680 +/- 0.004 when the molality of C8H5O4K was between 0.02 and 0.1 mol kg(-1).