To determine the standard electrode potential for the reaction Fe2+ → Fe3+ + e-, it is essential to understand that standard conditions imply activities of the substances equal to 1, not necessarily concentrations of 1 M. While using 1 M solutions of Fe2+ and Fe3+ may seem like a reasonable approximation, it does not yield accurate results due to the behavior of solutions at that concentration. The concept of a standard solution is hypothetical, as no true 1 M solution behaves as if it were infinitely dilute. Instead, standard electrode potentials are derived from extrapolating data from real solutions. To achieve accurate measurements, one should prepare a series of diluted ion solutions, measure their potentials, calculate ionic strengths, and determine activity coefficients, ultimately extrapolating to conditions where activities equal 1. However, calculating activity coefficients becomes challenging at ionic strengths above 0.1, complicating the process.
