The chemical potential or activity of ions cannot be determined on a purely thermodynamic basis. This is due to the fact that the effects of an ion cannot be separated from the effects of the accompanying counter-ion, or in other terms, the electrochemical potential of the ion cannot be separated into the chemical and the electrical component. Such a separation must necessarily be based on a non-thermodynamic convention. The present convention is based on the assumption that the molal activity coefficient of the chloride ion in dilute aqueous solutions (I < 0.10 mol kg-1) can be estimated by means of the Debye–Hückel equation: \[-\log _{10}\gamma _{\text{B}}=\frac{z_{\text{B}}^{2}\ A\ \sqrt{I}}{1 + \mathring{a}\ B\ \sqrt{I}}\] where I is ionic strength, z is the charge number of the ion, å is ion size parameter and A and B are temperature-dependent constants. According to the Bates–Guggenheim convention åB is taken to be 1.5 x sqrt(mol kg-1) at all temperatures and for all compositions of the solutions.