Which approach is used to account for changes in activity coefficients due to ionic strength?

• A. Use concentrations or ignore ionic strength.
• B. Use activities or Debye-Hückel corrections.
• C. Ignore ionic strength completely.
• D. Use standard state.

Answer: (B)

Activity coefficients quantify how ions interact in solution, so changes in ionic strength shift these coefficients away from 1. To account for that, you either work with the actual activities a_i = γ_i c_i or apply Debye-Hückel corrections to the γ_i themselves. Debye-Hückel theory links γ_i to the ionic strength I, describing how electrostatic interactions among ions alter the effective concentration that drives equilibrium. In dilute solutions, the classic form shows log γ_i decreases (or increases) with z_i^2 and sqrt(I); extended Debye-Hückel and related models extend this to higher ionic strengths by including ion size and specific interactions. So the correct approach is using activities or applying Debye-Hückel corrections to capture how ionic strength changes affect non-ideal behavior.