Abstract
A successive titration with EDTA was applied to the determination of Fe(III) and Fe(IV) in barium orthoferrate.
The recommended procedure was as follows. The sample was dissolved in hydrochloric acid containing a known excess of Fe(II) ion, by passing oxygen-free carbon dioxide under gradual heating. After cooling, the solution was diluted with distilled water saturated with carbon dioxide. An aliquot of the solution, added with the buffer solution (pH 2) deaerated by carbon dioxide, was titrated for Fe(III) with EDTA using salicylic acid as an indicator. Hexamine was then added to adjust pH to 5, and methyl thymol blue as an indicator. The solution was heated to 60°C, and titrated with EDTA to determine Fe(II) remaining in the solution. The amounts of Fe(III) and Fe(IV) in the sample were readily calculated from the values of Fe(II) and Fe(III) found by the above procedure.
These values agreed well with those calculated from the weight changes measured by a thermobalance.
