Solubility and thermodynamic studies of sparingly soluble tellurite salts

In the past few years, tellurium has attracted much attention as it is widely used in a large number of important industrial applications. Despite its importance, there is a lack of data on its salts in the literature. In this study, different sparingly soluble tellurite salts (e.g., Ag2TeO3, PbTeO3, CaTeO3, SrTeO3 and BaTeO3) were prepared and characterized using various techniques including powder X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectrometry, Fourier transform infrared spectroscopy and thermogravimetric analysis as well as differential scanning calorimetry. Moreover, the solubility and solubility product of these salts are studied by potentiometric method using carbon paste sensors. By applying standard and double standard addition methods, the tellurite ion content in the supernatant liquid (TeO32− ) was determined at 25 °C. The solubility products were confirmed by atomic absorption spectroscopy and complexometric titrations, which indicate the high sensitivity and accuracy of the proposed potentiometric method. In addition, thermodynamic parameters such as Gibbs free energy ∆G°, enthalpy ∆H° and entropy ∆S° of the dissociation process or solution were calculated using the Debye–Huckel equation via the determination of solubility of metal tellurite salts at different temperatures.