A reference electrode equipped with ionic liquid salt bridge consisting of tributyl(2-methoxyethyl)phosphonium bis(pentafluoroethanesulfonyl)amide has been employed for potentiometric precipitation titration of chloride with silver ions in water at 25 • C. A model for the titration curve was regressed to experimental curves, taking into account the change in the activity coefficients of relevant ionic species in the course of the titration, to obtain the least square estimates of two adjustable parameters in the model, the solubility product (K sp ) and the ana-lyte concentration. The least-square estimate of K sp , (1.840 ± 0.060)×10 − 10 , i.e., pK sp = 9.736± 0.014, is in good agreement with literature data, but with higher precision.