The equations for the relation between log10([SH+]/[S]) + H0 and log10[H+] + H0 for base S in aqueous mineral acid solution, where H0 is Hammett's acidity function and log10[H+] + H0 represents the activity function log10(γS.γH+)/γ.SH+ for the nitroaniline reference bases to build H0. \[\log _{10}(\frac{[\text{SH}^{+}]}{[\text{S}]})- \log _{10}[\text{H}^{+}]=(\varPhi - 1)\ (\log _{10}\text{[H}^{+}\text{]}+\text{H}_{0})+pK_{\text{SH}^{+}}\] \[\log _{10}(\frac{[\text{SH}^{+}]}{[\text{S}]})+H_{0}=\varPhi \ (\log _{10}[\text{H}^{+}]+\text{H}_{0})+pK_{\text{SH}^{+}}\]