The excess acidity of aqueous HCl and HBr media. An improved method for the calculation of X-functions and H₀ scales

Excess acidity (X-function) scales for 0–40% w/w aqueous HCl and 0–60% w/w aqueous HBr solutions are derived, using ionization ratio data for 29 and 9 weak bases, respectively; in these media the resulting PKBH+ values are quite similar to those obtained by standard acidity function treatments. A generalized derivation of the excess acidity enables the determination of pKR+ values for protonation–dehydration processes, some of which are given, and the study of partially dissociated acids. An improved computer program was used, applicable to smaller data sets (up to 50 bases); this program permitted a determination of the inherent precision of the derived functions, and a more rigorous evaluation of previously derived X-functions and the whole excess acidity method.