Determinación de la constante de estabilidad (KE) del ión triyoduro como una practica de laboratorio a micro escala

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Abstract

En este trabajo se propone una práctica a microescala para el laboratorio de química analítica en la cual se determina la constante de formación (Ke) del ión I3- por medio del equilibrio de reparto de yodo molecular entre un solvente orgánico y una solución de yoduro de potasio. Las cuantificaciones de I2 e ión triyoduro se realizan por espectrofotometría visible lo cual implica una reducción en la cantidad de reactivos utilizados y en el tiempo de duración de la actividad de laboratorio. Los estudiantes plantean los modelos químico y matemático, realizan mediciones, construyen graficas y analizan los resultados para obtener un valor de Ke. Los resultados obtenidos por la práctica a micro escala son iguales a los que se producen en la práctica tradicional. Además se incorpora el tratamiento de los residuos por medio de la purificación de solventes y neutralización de la acidez de las soluciones acuosas, lo que reduce el impacto ambiental. En general se puede afirmar que la propuesta presenta una serie de ventajas en cuanto a ahorro de recursos y tiempo.

Translated abstract

This paper proposes a laboratory activity for the course of analytical chemistry, that involves the determination of the equilibrium constant of I3- formation (Ke) through the partition of iodine between an organic solvent and an aqueous solution of potassium iodide. The quantification of I2 and I3- are made by visible spectrophotometric measurements, which implies a reduction in the amounts of reactive needed and are less time consuming. The students outline the chemical and mathematical models, make measurements, build graphics and analyze the results to obtain a Ke value. Results are similar to those obtained by the traditional laboratory activity. Also a protocol for the treatment of residues is incorporated to purify the solvent and for the neutralization of aqueous solution to reduce the environmental impact. En general speaking it can be said that the proposed activity have several advantages in the saving of resources and time.

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Most cited references 6

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XAFS analysis of triiodide ion in solutions

H Sakane, T Mitsui, H. Tanida … (2001)

Iodine K-edge XAFS of triiodide ions in various solvents were measured at SPring-8 BL01B1 and analyzed. Though the anion takes a linear and symmetric form, the second peak expected from enhanced multiple scatterings can be hardly observed because of its large vibrations. The bond distances and the Debye-Waller factors for the I-I couple vary when protic solvents were used and they were similar when aprotic solvents were used. It was indicated that the larger the Mayers' acceptor number of the solvent is, the larger the Debye-Waller factor is. It was also found that among the aprotic solvents, the larger the Gutmann's donor number is, the smaller the Debye-Waller factor is.