The dissociation constant (pK) of benzoic acid in a binary benzoic acid-water solution at 25 ± 0.5°C was determined using concentration-based UV/VIS spectrophotometry without the addition of titrants, buffer solutions, or background salts. The measured value was 4.294 ± 0.002, which differs from previously reported literature data. A new model accounting for the influence of symmetric and asymmetric electrolytes on acid-base equilibria is proposed. The observed dissociation constants of benzoic acid in aqueous salt solutions exhibit a nonlinear dependence on salt concentration in the range of 10 – 10 mol·dm. It was shown that as the concentration of a strong electrolyte decreases, the observed dissociation constants approach the value obtained in the pure solvent, i.e., the thermodynamic constant.
S.S. Lysova (Wed,) studied this question.