The chemical model presented is founded on the prediction of all chemical reactions taking place in a solvent extraction system. Starting from equilibrium constant expressions of these chemical reactions the corresponding mathematical formulae for calculation of the concentrations of distributing species are derived. If the required chemical reactions in the organic phase are involved, the model fits the experimental data and enables the calculation of the concentrations of distributing species in the organic phase within the concentration range in which the distribution of reacting species was measured.