Ionization constants of o-phthalic acid and standard pH values of potassium hydrogen phthalate buffer solutions in glycerol plus water solvent mixtures at normal and subzero temperatures

Determination of primary standards for pH measurements in glycerol + water solvent mixtures has been carried out based on reversible emf measurements of the cell Pt \H-2\ KHPh (m(PS)) + KCl (m(Cl))\ AgCl \ Ag/Pt where KHPh denotes the potassium hydrogen phthalate buffer solution of mola lity m(PS) = 0.05 mol-kg(-1), at glycerol mass fractions, w(G) = 0.2 and 0. 4, within the temperature range -10 to 40 degreesC. A multilinear regressio n procedure as a function of electrolyte molality, glycerol mass fraction w (G). and temperature T has been applied for the data processing leading to the values of primary standards pH(PS). These can be represented by the fol lowing regression equation pH(PS) = (4.007037 +/- 0.001113) + (3.55844 +/- 0.01776)x(G). +(0.39622 +/- 0.01410)z + (4.3084 +/- 0.3377)z(2) -(50.66 +/- 10.53)x(G) z(2) + (457.10 +/- 78.48)x(G)(2) z(2) where z = (T - 298.15)/298. 15. Parallel values of the first ionization con stant oro-phthalic acid (H2Ph, benzene-1,2-dicarboxylic acid, the parent ac id of KHPh). which are essential for the above calculations, have been dete rmined from reversible emf measurements of the cell Pt/H-2/H2Ph (m(1)) + KHPh (m(2)) + KCl (m(3))\ AgCl \ Ag \ Pt over the range of solvent composition and temperatures mentioned above.