A simplified form of Stokes–Robinson equation

In non-associated dilute aqueous electrolyte solutions, the deviation from ideality is principally attributed to the interionic interactions and hydration of ions. Stokes and Robinson combined Bjerrum's thermodynamic treatment of ion–solvent interactions with Debye–Hückel treatment of interionic interactions to obtain a two-parameter equation. In very dilute regions, the Stokes and Robinson's equation reduces to a much simpler form, i.e.[Formula: see text]Activity coefficients of an electrolyte at lower concentrations, say up to 0.1 m, can be calculated from the equation provided suitable values of &([a-z]+); and h are available. Solutions of hydrogen chloride and sodium chloride were chosen as examples. The results agree with the existing data very satisfactorily.