Reduction in the presence of sulfuric acid, phosphoric acid, boric acid or silicic acid

Abstract

The oxidation of a compound of low-valence state is an increase of its valence, and it means a transition of a substance from basic to acidic. It is then obvious from the law of chemical equilibrium that the reaction proceeds in the presence of a base which removes acid from the system. It is nowadays understood as one of well-known chemical rules.
The reversed rule, the reduction in the presence of acid, which may be naturally expected is, however, scarcely recognized, and only few examples have been known.
The author has shown in his experiments the reduction of Mn(VII), Mn(IV), Cr(VI), V(V), Mo(VI), W(VI) and U(VI) in the presence of H₂SO₄, H₃PO₄, H₃BO₃ or SiO₂, and asserts the presence of the above rule. In addition, he reduced V(V) by H₃PO₄ and oxidimetrically titrated it and discussed the propriety of representing monazite by CePO₄ and rhodonite by MnSiO₃.