The radial profiles of the mean force and corresponding potential of mean force for the Cl-. . .H3O+ pair are determined by constraint molecular dynamics of an infinitely dilute near-critical aqueous solution, as described by the SPC/E water model and either the Gertner-Hynes or the Kusaka hydronium model. These profiles are used to test the prediction of a continuum primitive model, and to predict the ion-pair association constant. The reliability of these intermolecular potential models is assessed by comparing the predicted association constants with those determined experimentally by conductance and solubility measurements. This comparison suggests that the most accurate experimental data available for the association constant of HCl fall between the predictions of the two models, and tends to support the superiority of the Gertner-Hynes over the Kusaka hydronium model. Moreover, the simulation results allow a quick test of the reliability of the simple continuum dielectric model to represent the solvation behavior of the ion-pair in solution.