On the activity of ions and the junction potential: Revised values for all data

Abstract

This work presents an in-depth study of the interrelation between the junction potential

On the measurement of the real values of individual ionic activities: A chemical engineering perspective

“…The basic question is: 'Are the ionic activity coefficients measurable as claimed by us (Khoshkbarchi and Vera, 1996;Wilczek-Vera et al, 2004, 2010Wilczek-Vera and Vera, 2009a) and also by other researchers (Shatkay and Lerman, 1969;Lee et al, 2002;Schneider et al, 2003Schneider et al, , 2004Zhuo et al, 2008) or, as claimed by Malatesta (2009Malatesta ( , 2010 the real values are still unknown?' The term 'real' is used here in the sense of the actual value of the physical property, the value that can be used for chemical engineering design.…”

Activities of aqueous Na+ and Cl- ions from homoionic measurements with n

“…In fact, the term (E T J,∞ − E T J,k ) is the true potential that it would exist in a junction between the most dilute solution of the run and a solution of composition m k . If the latter is in the calibration region, this will be the junction potential between two very dilute solutions in contact, which is well approximated by the Henderson Equation (Wilczek-Vera et al, 2004). Thus, to a very close approximation in the calibration region, the calculated value of junction potential between these two solutions (E J,∞ − E J,k ) will cancel the value of the true junction potential (E T J,∞ − E T J,k ).…”

“…In its simpler form, it uses the potentiometric form of Henderson equation (Wilczek-Vera et al, 2004) as a first crude approximation to calculate the liquid-junction potential, E J,k . The response of the ISE is then calibrated assuming that the ionic activity coefficients at high dilution (< 0.01 m) take the values given by the Güntelberg equation (Pitzer and Brewer, 1961).…”

“…As mentioned above, this was previously done for NaCl, NaBr, KCl and NH 4 Cl using 4 M KCl and 2 M NH 4 Cl solutions in the reference electrode and no noticeable difference was observed in the ionic activities so obtained. On the other hand, the activities of the ions Na + and Cl − in NaCl aqueous solutions were found to be one of most sensitive to the change of sign of the junction potential (Wilczek-Vera et al, 2004). Thus, the NaCl system was chosen for this study and it was decided to use a NaCl solution, saturated with AgCl, in the reference electrode.…”

“…One of the ISEs is sensitive to the cation and the other to the anion of the electrolyte in the sample solution. In the potentiometric convention (Wilczek-Vera et al, 2004), the schematics of the cell formed by the reference electrode and one ISE sensitive to ion i is represented as…”