On the isohydricity concept--some comments.

The isohydricity property, referred to systems composed of acids or bases, is presented. The related isohydricity conditions are formulated for different pairs of solutions. The pH titrations in the system of isohydric solutions are put in context with conductometric titrations.

Determination of dissociation parameters of weak acids in different media according to the isohydric method.

The isohydricity (pH constancy) principle is referred to the pair of solutions: weak acid (HL, C(0)mol/L) and strong acid (HB, C mol/L) when mixed e.g., according to titrimetric mode.

A new sensitive method of dissociation constants determination based on the isohydric solutions principle.

The paper provides a new formulation and analytical proposals based on the isohydric solutions concept. It is particularly stated that a mixture formed, according to titrimetric mode, from a weak acid (HX, C(0)mol/L) and a strong acid (HB, Cmol/L) solutions, assumes constant pH, independently on the volumes of the solutions mixed, provided that the relation C(0)=C+C(2)·10(pK(1)) is valid, where pK(1)=-log K(1), K(1) the dissociation constant for HX. The generalized formulation, referred to the isohydric solutions thus obtained, was extended also to more complex acid-base systems.

Modelling of acid-base equilibria in binary-solvent systems: A comparative study.

A new approach to modelling of some binary (hydro-organic, HL/H(2)O+B) acid-base systems with organic co-solvent B fully miscible with water, is suggested and applied for the determination of acidity parameters pK for some weak acids HL. The models are designed to get the pK=pK(x) relationships (x-mole fraction of B in H(2)O+B) from results of pH titrations made in such systems and for the determination of pK(B)=pK(1) for HL in pure B. The Redlich-Kister equation, together with its asymmetric extensions, and the Legendre functions with orthogonal polynomials, appeared to be suitable for such purposes.