Spectrophotometric studies of the metavanadate system. I. Solution equilibria
Australian Journal of Chemistry
26(6) 1173 - 1181
AbstractSpectrophotometric absorbance measurements on sodium metavanadate solutions in the region 240-300 nm were made at 10°, 25°, and 40°C on: (1) a series of solutions 2.46 x 10-5M in vanadium and covering the pH range 7-9; and (2) a series of solutions at constant pH and covering the concentration range from 4x10-5 to 1.2x10-2M. All solutions contained 3.0M NaClO4 and 0.10M Tris buffer. From these data were computed the extinction coefficients of HVO42-, H2VO4-, and (VO3-), as well as the pKa of H2VO4- (7.62±0.07). Metavanadate is probably a mixture of V3O93- and V4O124- under the conditions of the experiment. Upper limits on the formation constants at 25° are K3 = 10.8±0.5x106 12 mol-2 and K4 = 73±7x 10913 mol-3. The temperature dependence of the data gives for the enthalpy of polymerization, ΔH° = -21±2 kJ mol-1 H2VO4-.
© CSIRO 1973