The M_Cactivity coefficient function for acid–base equilibria. Part I. New methods for estimating pk_avalues for weak bases

Abstract

An experimental linear relation in strong aqueous acids between overlapping indicators, available for the whole aciditv range, allows the determination of the pK, values of weak bases by a new method of approximation. A new activity coefficient function (Mc) in aqueous sulphuric and perchloric acid is also proposed. The thermodynamic equilibrium constants of various groups of compounds including primary nitroanilines, tertiary amines, amides, indoles, alkoxy-and hydroxy-benzenes, triphenylmethyl alcohols, and sulphoxides, have been reinvestigated and the results compared with those reported in the literature. The solvation effects of the medium on the Ma function are also discussed.

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

“…The AF values and those extrapolated using X (eq. [4]) are quite similar, the average deviation between them being k0.16pK units (Table 2). This, however, is three times as large as the average of the standard deviations of the X-function values in the table.…”

“…The excess acidity X is expressed as a polynomial in the concentration unit involved, percent by = 0 is the hypothetical ideal 1 M solution of the acid weight w here; substitution into eq. [4] gives an eq. [5] for each used, the same as for pH measurements.…”

“…[I], and eq. [41 has seen extensive use for extrapolative pKBH+ is defined in terms of molar concentra-PKBH+ determinations in these media (4)(5)(6)(7)(8). Retion C and molar activity coefficients f as in eq.…”

“…This is a limitation on the generality of X, since this definition leads to an excess of compounds with large m*'s producing a steep X-function, and an excess with low m*'s producing a shallow one (see eq. [4]). Thus X will only be a unique function of the medium if a reasonably large and representative set of bases is available (i.e.…”

“…Straight-line plots according to eqs. [4] and [lo] were calculated using a standard weighted line-fitting routine from Bevington . I 8 (lo), as before (6).…”