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Thermochemical redox equilibria of ZoBell's solution

Authors
Journal
Geochimica et Cosmochimica Acta
0016-7037
Publisher
Elsevier
Publication Date
Volume
41
Issue
12
Identifiers
DOI: 10.1016/0016-7037(77)90215-0

Abstract

Abstract The redox potential of ZoBell's solution, consisting of 3.33 × 10 −3 molar K 4Fe(CN) 6, 3.33 × 10 −3 molar K 3Fe(CN) 6 and 0.10 molar KCl, has been measured by a polished platinum electrode vs a saturated KCl, Ag/AgCl reference electrode. Measurements in the temperature range 8–85°C fit the equation E( volts) = 0.23145 − 1.5220 × 10 −3 (t − 25) − 2.2449 × 10 −6(t − 25) 2 where t is in degrees Celsius. Evaluation of literature data was necessary to obtain a reliable value for the Ag/AgCl half-cell reference potential as a function of temperature. Combining the measurements from this study with the literature evaluation of the Ag/AgCl reference potential yields the temperature dependent potential for ZoBell's solution: E( volts) = 0.43028 − 2.5157 × 10 −3 (t − 25) − 3.7979 × 10 −6 (t − 25) 2 relative to the standard hydrogen potential. From these data the enthalpy, entropy, free energy and heat capacity for the ferro-ferricyanide redox couple have been calculated. The temperature equation for the potential of ZoBell's solution may be used for checking potentiometric equipment in the determination of the redox potential of natural waters.

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