Freezing point depression in the binary NaVO3 –H2O and NH4VO3 –H2O Systems at 𝑝� = 0.1 MPa

Abstract

Abstract

The freezing point depressions in the NaVO3 – H2O and NH4VO3 – H2O systems have been determined at 𝑝 = 0.1 MPa from molalities of ca. 0.005 mol kg−1 up to near saturation. The present data significantly expand the almost non-existent database of excess thermodynamic properties of binary V(V) – H2O systems. The data could be explained within their experimental uncertainties by a thermodynamic model considering the association of the dihydrogenvanadate ion (H2VO4 – ) to V4O124 – (aq) and representing the excess Gibbs free energy (𝐺Ex) by the Pitzer equations with two adjustable parameters. The magnitudes of the determined parameters for the second virial coefficient of Na+-V4O124 – interaction were typical for 4-1 electrolytes. The same model could describe also the data for the NH4VO3 – H2O system as even the saturated solution is sufficiently dilute that the contribution of short range interactions to 𝐺Ex is small.