The paper deals with non-linear least square algorithm applied to determine simultaneously equilibrium constant pKb or log , activity coefficients of ions HA+ and of neutral molecules fA for aqueous solution of monoprotic bases from pH data at different ionic forces established by inert salts. It has been shown that the calculation results of log HA+, logfA and log as well could be in a very good agreement the not so large number of experimental data when the experimental data are fully treated in order to receive INPUT data with high precision.
