Thermodynamic Properties and Equilibrium Solubility of KH5P2O8(aq) at Different Temperatures, Experimental Study, and Thermodynamic Modeling

The thermodynamic properties and equilibrium behavior of the solubility relevant to aqueous solutions of potassium pentahydrogendiphosphate were studied at different temperatures. The experimental water activities of the KH5P2O8(aq) were measured in the molality range up to saturation solutions ranging from 298.15 to 353.15 K by the hygrometric technique. The Pitzer and Clegg-Pitzer-Brimblecombe models were developed from the new experimental results to access the interaction parameters of the binary system. The binary parameters were estimated for KH5P2O8-H2O, considered a charge-type 1-1 electrolyte, and used to evaluate the activity and osmotic coefficients for both models. This approach, with the interaction parameters in the studied temperature interval, exhibits excellent agreement with the osmotic coefficient data over the full molality range. Experimental solubilities of KH5P2O8 in aqueous solutions were also measured up to m(max) = (6.723, 10.496, 16.566, and 25.152) mol<middle dot>kg(-1) from (298.15, 313.15, 333.15, and 353.15) K, respectively. The calculated solubilities using the data from the two models were evaluated and showed good agreement with the experimental results. The resulting precipitated solids at various temperatures are analyzed, revealing only the crystalline form of KH5P2O8(s). The Gibbs molar energies of dissolution and solubility products are also calculated at different temperatures.