Consider the following half-reaction, for which
E° = +0.222 V: AgCl(s) + e- ? Ag(s) + Cl-(aq)
With a saturated KCl fill solution, the potential of this half-reaction is +0.197 V. Use the Nernst equation to calculate the activity of the chloride ion in the fill solution. At 25 °C, saturated KCl is ~4.0 M. Why does the calculated activity differ from this concentration?