Advances in Engineering Advances in Engineering features breaking research judged by Advances in Engineering advisory team to be of key importance in the Engineering field. Papers are selected from over 10,000 published each week from most peer reviewed journals.
Grazyna Wilczek-Vera, Juan H. Vera
Chemical Engineering Science, Volume 66, Issue 17, September 2011
Abstract
This work demonstrates the perfect analogy between the standard method for determining activities in non-electrolyte mixtures and the method used for the determination of ionic activities in electrolyte solutions. For the case of electrolyte solutions, the general procedure of solving three equations with three unknowns is discussed and the reasons why this procedure failed to work for the case of KCl solutions are recapitulated. A modified iteration procedure implemented in this work gives convergence of the solution after three iterations. The crucial difference between eliminating the junction potential, by combination of independent equations, and the use of a proper estimate of its value is emphasized. A new model-free calibration procedure is proposed and sample calculations of K+ and Cl− activities in KCl aqueous solutions are presented. Values of K+ and Cl− activities in KCl aqueous solutions obtained by this new procedure and by a variety of other methods and researchers are compared.
Additional Information
A Reflection Regarding the Measurability of Ionic Activities
Juan H. Vera and Grazyna Wilczek-Vera
Retired Academics, McGill University, Montreal, QC, Canada
At the onset of ion-selective electrodes (ISE’s), Bates and Robinson1 noted that if it were possible to make ISE measurements with a constant value for the junction potential one would directly obtain the individual activity of the ionic species to which an ISE responds. While this is true, this manuscript provides experimental and theoretical evidence showing that, when the ISE is properly calibrated, a variable junction potential does not affect significantly the values of the ionic activities. On the other hand, as illustrated by a recent debate prefaced by R. D. Weir2, the arguments contesting the possibility of measuring individual ionic activities are only supported by calculations based on thought experiments irrelevant to these measurements. This brings to mind an example with which Bertrand Russell illustrates the disrespect often held for experimental observation which contradicts a traditional belief. In a writing on ‘Science and Tradition’3, Russell describes the case of an orthodox group that maintained that there were no moons orbiting around Jupiter. So, when Galileo’s telescope showed their existence, they refused to observe them, arguing that what it was shown by the telescope was surely deceptive. In the case of individual ionic activities, all that is required is to measure the voltage response of an ion-selective-electrode (ISE) against a single junction reference electrode and apply Nernst equation4. In recent work5, we have further elaborated on arguments against a tradition which denies the possibility of measuring individual ionic activities. Furthermore, recently D. Fraenkel6 presented a new theory of electrolyte solutions that supports our results. As we have done previously, we invite interested researchers to repeat our experiments and verify the results of our calculations.
References
- R. G. Bates and R. A. Robinson, ”Trends in the Standarization of Ion Selective Electrodes”, Conference on Ion Selective Electrodes, Budapest, 1977, E. Pungor and I. Buzas, Editors, Elsevier Scientific Publishing Company, Amsterdam, Oxford, New York, 1978.
- R. D.Weir, “Preface to the Following Four Notes”, J. Chemical Thermodynamics, 47, 411 (2012). The four notes of the debate follow in pages 442-452 of the same issue.
- B. Russell, The Impact of Science in Society, page 19, Routledge, London and New York, 1976.
- Wilczek-Vera, G., Rodil, E., Vera, J.H., “A complete discussion of the rationale supporting the experimental determination of individual ionic activities”. Fluid Phase Equilibria 244, 33-45, (2006)
- G. Wilczek-Vera and J.H. Vera, “The activity of individual ions. A conceptual discussion of the relation between the theory and the experimentally measured values.” Fluid Phase Equilibria, 312, 79-84, (2011). Corrigendum Fluid Phase Equilibria, 314, 203 (2012).
- D. Fraenkel, “The single-ion activity: Experiment versus Theory”, J. Phys. Chem. B, 116, 3603-3612 (2012)
Go to Journal
