Distribution Potential for an Acid

At equilibrium, we have equality of the electrochemical potentials of the two ions A- and H+ in the two phases (ignoring the presence of OH- ions), we have the equality of the chemical potentials of the acid AH in the two phases, and we also consider the acid-base equilibria in both phases. As a result, the Galvani potential difference is given by the distribution potential of the A and H+ ions, and the acidity constant in the organic phase is linked to that in the aqueous phase by 

This equation shows that, to calculate the pA ° of an acid in the organic phase knowing its pA valne in water, we need to know the standard distribution coefficients of the varions species involved. 

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