Iridio: Una opción para medir el potencial redox
Fuente:
Ciencias Marinas
Some relevant results are presented of research leading to an alternative redox electrode to platinum. Several different electrodes were subjected to experiments under controlled conditions, mainly in artificial seawater. Among those tested were platinum, graphite, glassy carbon, gold and iridium. O...
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| Published in: | Ciencias Marinas |
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| Main Authors: | , , |
| Format: | Artículo científico |
| Language: | English |
| Published: |
Universidad Autónoma de Baja California, Instituto de Investigaciones Oceanológicas
2003
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| Summary: | Some relevant results are presented of research leading to an alternative redox electrode to platinum. Several different electrodes were subjected to experiments under controlled conditions, mainly in artificial seawater. Among those tested were platinum, graphite, glassy carbon, gold and iridium. Our results, when combined with those estimated by using a model based on the MINEQL+ program, suggest that the O2/H2O2 redox couple is the one that controls the redox potential under these experimental conditions. In well-oxygenated waters (PO2 = 0.21 atm) and pH = 8, the value calculated for EH = 0.748 V and the pE at the surface should read 12.67 (pE = (F/2.3RT) EH = 12.67). However, in practice, the redox potential experimentally measured was only between +0.45 and +0.50 V. Additionally, the presence of H2O2 was determined from our own measurements. Its concentration was estimated at about 10–8 M. This value is in good agreement with values measured and reported by other authors for surface waters under natural conditions. The four sets of measurements that were carried out were: measurements where the O2 concentration of the solution was changed and the pH was kept constant (and vice versa); measurements of several redox couples (including Fe2+/Fe3+, NO3–/NO2– and I3–/I–); measurements in mud flats at San Quintín, Baja California; and measurement of the redox potential in natural seawater and in filtered and UV seawater. Most measurements indicate that the electrode with a response closest to that predicted by thermodynamics is the Ir electrode. We also found that the reaction of Pt, when compared to Ir, appeared to be slow.
Se presentan los resultados relevantes en la búsqueda de un electrodo alternativo al platino para mediciones redox. Para estos ensayos se usó un grupo de cinco electrodos inorgánicos inertes (platino, grafito, carbón vitrificado, oro e iridio). Nuestros resultados, respaldados con cálculos de modelos termodinámicos, utilizando el programa MINEQL+ sugieren que, a diferencia de otros estudios, la pareja O2/H2O2 es la que controla el potencial redox bajo las condiciones experimentales llevadas a cabo en este trabajo. En aguas bien aireadas (PO2 = 0.21 atm) y con pH = 8, el valor del EH = 0.748 V y del pE en la superficie es de 12.67 (pE = (F/2.3RT) EH = 12.67). Sin embargo, en la práctica, el potencial medido experimentalmente, tanto por el electrodo de Pt como por el de Ir, es de entre +0.45 a +0.50 V. Adicionalmente, la presencia de H2O2 fue deducida a partir de nuestras mediciones y su concentración fué estimada en valores cercanos a 10–8 M, coincidiendo con valores reportados por otros autores para aguas naturales. Las mediciones a que se sometieron los electrodos de Pt y de Ir fueron: variaciones de O2 manteniendo el pH constante y viceversa; mediciones de algunos pares redox comunes en agua natural pero medidos en agua de mar sintética (se incluyeron Fe2+/Fe3+, NO3–/NO2– y, I3–/I–); mediciones en medio natural en planicies lodosas de San Quintín, Baja California; y finalmente se hicieron mediciones de potencial redox en agua de mar natural sin filtrar y en agua de mar natural filtrada y oxidada mediante luz UV. Los resultados muestran que las respuesta más cercanas a las predichas por un modelo termodinámico se obtienen con el electrodo de Ir. El electrodo de Pt en general pareció responder de manera mas lenta que el Ir. |
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