What factor is most directly altered by salt concentration in an aqueous solution to affect electrode potentials, and how is it accounted for?

• A. Temperature changes the electrode potentials directly; corrected by adjusting the temperature in the Nernst equation.
• B. Ionic strength affects activity coefficients; corrected by using activities or Debye-Hückel framework.
• C. Pressure affects electrode potentials; corrected by applying Boyle's law.
• D. Solvent dielectric constant is the sole factor; corrected by using standard state.

Answer: (B)

Electrode potentials come from the activities of the reacting species, not just their raw concentrations. When you add salt to water, you raise the ionic strength of the solution. This changes how strongly ions interact with each other, which alters their activity coefficients (the gamma factors). In the Nernst equation, the relevant quantity is the activity a_i = gamma_i times the concentration. As ionic strength increases, gamma_i departs from 1, so the effective activity—and thus the potential—shifts even if the concentrations are the same.

To account for this, you replace concentrations with activities in the Nernst equation and estimate the activity coefficients using models like Debye-Hückel (or extended forms such as Davies or SIT) that relate gamma to ionic strength. That’s why the factor most directly affected by salt concentration is the ionic strength, via changes in activity coefficients, and the correction is through using activities calculated with Debye-Hückel-type theories.