Enthalpy of solution of potassium tetrafluoroborate in water and in aqueous sodium fluoride. Thermodynamic properties of the aqueous tetrafluoroborate anion and potassium tetrafluoroborate

An adiabatic calorimeter was used to measure the enthalpy of solution of potassium tetrafluoroborate (0.01 mol center dot kg(-1) to 0.02 mol center dot kg(-1)) in water and in aqueous sodium fluoride of different ionic strengths (0.2 mol center dot kg(-1) and 0.5 mol center dot kg(-1)) at 298 K and 313 K. The present results yield the standard-state enthalpy and heat capacity for the solution process and, when combined with literature values for solubilities, yield the standard-state entropy of the solution process. From these properties, and previous measurements involving potassium tetrafluoroborate, we provide a new analysis of thermodynamic properties of the aqueous tetrafluoroborate ion and compare these new properties to previous tabulations and explain the sources of discrepancies in the literature.