The solubility of molybdenum trioxide in various mineral acids

Equilibrium solubility values for MoO3·H2O at 20°C in HCl, HNO3 and H3PO4 solutions of various molarities are reported. The solubility of molybdic oxide in nitric acid first rises and then falls, and is zero in concentrated nitric acid. This anomaly is explained on the basis of Pryor and Evans' theory of defect-controlled dissolution of oxides in acids. A much larger anomalous maximum in the solubility of MoO3 in phosphoric acid is explicable on the basis of complex formation.