In what follows, pK a 's will be numbered pK a1 , pK a2 , pK a3 and pK a4 and we will always consider pK a1 < pK a2 < pK a3 < pK a4 . The associated concentrations may also be numbered C 1 , C 2 , C 3 and C 4 . We will note ∆pK a the difference between the highest pK a values and pK a1 (as it is the smallest one by definition here). We will neglect ionic strength effects, hence activities reduce to concentrations in the equilibrium constants, and we will use the shorthand notation [H 3 O + ] = h.