Term: Cox–Yates equation
https://doi.org/10.1351/goldbook.C01386

Definition:
A modification of the Bunnett–Olsen equation of the form: \[\log _{10}(\frac{[\text{SH}^{+}]}{[\text{S}]})- \log _{10}[\text{H}^{+}] = m^{*}\ X + \text{pK}_{\text{SH}^{+}}\] is the activity function \[\log _{10}(\frac{\gamma _{\text{S}}\ \gamma _{\text{H}^{+}}}{\gamma _{\text{SH}^{+}}})\] for an arbitrary reference base. The function X is called the excess acidity because it gives a measure of the difference between the acidity of a solution and that of an ideal solution of the same concentration. In practice \[X=- (\mathrm{H}_{0}+\log _{10}[\mathrm{H}^{+}])\] and \[m^{*}=1- \mathit{\Phi }\]

Related Terms:
1) bunnett–olsen equation (http://doi.org/10.1351/goldbook.B00758).
2) excess acidity (http://doi.org/10.1351/goldbook.E02234).
3) acidity (<em>of a compound, of a medium</em>) (http://doi.org/10.1351/goldbook.A00079).

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1101 (https://doi.org/10.1351/pac199466051077)

Citation: 'Cox–Yates equation' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.C01386

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