Solubility of Barium Arsenate

Current thermodynamic data suggest barium arsenate [Ba 3 (AsO 4 ) 2 (c)] to be a highly stable phase. However, sufficient evidence is available to question the validity of the current data. In order to determine the solubility (p K sp ) and calculate the standard free energy of formation (Δ G° f ) of Ba 3 (AsO 4 ) 2 (c), an equilbrium solubility study was conducted. The equilibrium experiments were carried out under three different ionic strength conditions for reaction times up to 45 d. Equilibrium was approached from both undersaturated and supersaturated initial conditions. The p K sp for the dissolution of Ba 3 (AsO 4 ) 2 (c) was calculated to be 21.62. Correspondingly, a Δ G° f of − 3101.2 ± 2.0 kJ mol −1 was calculated. This value is 166.9 kJ mol −1 more positive than the current literature value. Reevaluation of the solubility data from a previous work suggests that the p K sp for the dissolution of BaHAsO 4 · H 2 O(c) is 24.64 and the corresponding Δ G° f is − 1587.0 ± 2.5 kJ mol −1 .