The Formal Oxidation-Reduction Potentials of Ferric-ferrous in Phosphoric Acid
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Authors
McFall, Inez Elizabeth
Issue Date
1954
Volume
Issue
Type
Thesis
Language
en_US
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Abstract
The formal redox potentials of the ferric-ferrous system have been determined in the media of perchloric (15), nitric (12), hydrochloric (13), sulfuric (15), and phosphoric (l) acids. The acids are named in the order of increasing extent to which the oxidation potential of the ferric-ferrous system is lowered in the presence of the acid. These formal potentials are more practical than the standard potentials because in the laboratory procedures involving ferric and ferrous iron, one or more of the above acids is generally present. For example, in the Zimmerman-Reinhardt method for the determination of iron in an ore, hydrochloric, sulfuric, and phosphoric acids are present. |The formal potentials determined by Carter and Clews (1) of Ferric-ferrous in phosphoric acid were carried out in acid concentrations of 4. 3-15. 811. These concentrations were necessarily high in order to dissolve the ferric and ferrous phosphates used. The values obtained are not applicable to ordinary quantitative procedures in which the concentrations of phosphoric acid are considerably less. The experiments of Carter and Clews were carried out at 17°C and calculations were made using 0. 560v for the standard, potential of the normal calomel electrode. The potential for this electrode is generally accepted as 0. 280v (14). |The purpose of the present work is to determine the formal redox potentials of ferric-ferrous in dilute concentrations of phosphoric acid and under conditions which are normally present in the laboratory. An attempt will be made to explain why the formal potentials of ferric-ferrous in phosphoric acid are much lower than the formal potentials of this system in the other acids mentioned.
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Creighton University
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