Identification of Fe (IV) in oxides by chemical test methods

Abstract

A comparative analysis of the behavior of oxides containing Fe (III) and Fe (IV) in redox reactions with organic and inorganic reagents has been carried out. SrFeO3-x oxide obtained by solid-phase synthesis from SrCO3 and Fe2O3 has been an object to develop test methods. It has been shown that Fe (IV) exhibits the properties of a stronger oxidizer than Fe (III), thus providing a set of reagents which enable identification of Fe (IV): hydrobromic acid, Fe2+ complex with V (IV), and Mn (II) salts, and organic reagents, namely, amines (diphenylamine, o-tolidine, benzidine) and dyes (methyl red). Potentiometric method proved stronger oxidative properties of Fe (IV) compared to Fe (III) revealed in different character of changes in EMF during dissolution of the corresponding oxides in HCl. SrFeO3–x oxide does not oxidize Mn (II) to Mn (VII), Cr (III) to Cr (VI), Ce (III) to Ce (IV) in acidic media, and Cu (II) to Cu (III) in alkaline media. Since the oxide under study oxidize Cl– = 1.3583 V) and Br– = 1.087 V) ions to the corresponding halogens, but does not oxidize Mn2+ to = 1.51 V), an estimated value of the standard redox potential is ~1.4 V. We have developed for the first time a system of analytical tests for differentiation of Fe (IV) and Fe (III) which can provide monitoring of the synthesis of complex oxides and phase formation in the systems containing iron, alkali and alkaline earth metals.