Australian Journal of Chemistry Australian Journal of Chemistry Society
An international journal for chemical science

Spectrophotometric studies of the metavanadate system. I. Solution equilibria

PH Rieger

Australian Journal of Chemistry 26(6) 1173 - 1181
Published: 1973


Spectrophotometric 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

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