2014 年 60 巻 2 号 p. 99-109
The criticism to the concept and use of single ion activity raised by de Levie (2010) has been examined. The lack of falsifiability in the concept of single ion activity, which he claims, led him to categorize the single ion activity as one of non-falsifiables, typified by the emperor’s new clothes (2012). However, his criticism is overeager, because the single ion activity can be estimated with a reasonable certainty, whose degree varies with a nonthermodynamic assumption employed, though. Electrochemistry is intrinsically nonthermodynamic, although in many of electrochemistry textbooks its cell voltage is correlated with the Gibbs energy of a redox reaction that would proceed in a homogeneous solution between the two redox couples, which are employed in the electrochemical cell. Ironically, such oversimplified understanding or picture of the nature of electrochemical cells partly justifies the criticism raised by de Levie. The obscurity associated with nonthermodynamic nature of electrochemical cells translates to the obscure interpretation of the Nernst equation in the form, E = E0 + (RT/F)ln(aOx/aRd), which has long been applied to a working electrode in electroanalytical chemistry. By focusing on this obscurity, it is possible not only to make our understanding of electroanalytical chemistry clearer but to design an electrochemical cell for less obscure, more reliable estimation of single ion activities.