Application of ferrous-chromate and iodometric titration for the determination of copper oxidation states in the superconductor YBa2Cu3Oy

Summary Oxidation-reduction titration methods, Fe²⁺-Cr₂C ₇ ^2– and I^–-S₂O ₃ ^2– , were applied to the determination of the oxidation state of copper in the superconductor YBa₂Cu₃O _y , and related compounds. The former method presented problems in the sample dissolution and titration steps. The dissolution of the sample in low concentrations of Fe⁺-phosphoric acid and Fe²⁺-perchloric acid takes place in two steps, the oxidation of Fe²⁺ to Fe³⁺ and the liberation of oxygen gas, when the liberation results in low analytical values for Cu⁺. In addition the coexistence of cuprous ion and acids induces the oxidation of ferrous ion by dissolved oxygen and air. The problems were resolved by dissolution in 0.1 mol/l Fe²⁺-phosphoric acid and titration in an argon atmosphere. The latter method gave good results by controlling the amounts of potassium chloride, the concentration of acetic acid, and by elimination of the dissolved oxygen in acetic acid solution. The results of the two titration methods coincided with each other.

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Anwendung der Eisen(II)-Chromat- und der iodometrischen Titration zur Bestimmung der Oxidationsstufe des Kupfers im Supraleiter YBa₂Cu₃O _y