Isopiestic Determination of the Osmotic and Activity Coefficients of K2HPO4(aq), Including Saturated and Supersaturated Solutions, at T=298.15 K

Abstract

The osmotic coefficients of K2HPO4(aq) have been measured at T=298.15 K by the isopiestic vapor pressure method over the range of molalities from 1.3846 mola lt ...kg(-1) to 13.939 mola lt ...kg(-1) (oversaturation) with CaCl2(aq) as the reference solution. The molalities and osmotic coefficients of saturated solutions in equilibrium with K(2)HPO(4)a lt ...xH(2)O(cr) were measured simultaneously by the same method. Available literature osmotic coefficients of K2HPO4(aq) at T=298.15 K, and our new experimental data, were combined and modeled using an extended form of Pitzer's equation and the Clegg-Pitzer-Brimblecombe equation based on the mole-fraction-composition scale. These equations were used to calculate the activity coefficients of K2HPO4(aq) at T=298.15 K.