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In general, concepts such as chemical equilibria and classical analytical chemistry, as well as instrumental methods such as potentiometry and flow injection analysis (FIA), are taught separately in the curricula of chemistry-related degree programs. However, FIA provides an opportunity to connect all of these important topics. This article shows how simple experiments can be used to link the fundamentals of FIA and potentiometry to the fundamentals of chemical equilibria and teach them in a sustainable way. The experiments were designed for undergraduate environmental science students with basic knowledge of chemical equilibria and classical analytical chemistry and minimal knowledge of electrochemistry. However, they can also be integrated into various courses on instrumental analysis in chemistry-related degree programs.
The potential of several ion-sensitive electrodes responds to the incorporated cations and anions. This has led some authors to misinterpret the potential of metal salt membrane electrodes and of electrodes of the second kind. Neglecting the kinetics of potential establishment and interpreting the potentials solely based on thermodynamics produce completely irrelevant data and suggest that ion concentrations down to 10−45 mol L−1 are accessible by simple potentiometric measurements. The switching from cation to anion response mechanism cannot be derived from thermodynamic equations. It bears complete similarity to the switching of response in the case of foreign interfering ions.
Electrochemically active ϵ‐MnO2 and ɣ‐MnO2 as tunnel‐type host‐guest structures have been extensively studied by crystallography and electrochemical techniques for application in battery cathode materials. However, the Gibbs energies of the underlying ion and electron transfer processes across the electrode interfaces have not yet been determined. Here we report for the first time these data for ϵ‐MnO2. This was possible by measuring the mid‐peak potentials in cyclic voltammetry and the open‐circuit potentials under electrochemically reversible conditions.