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

摘要

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 molality 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 regression 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 following 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 constant oro-phthalic acid (H2Ph, benzene-1,2-dicarboxylic acid, the parent acid of KHPh). which are essential for the above calculations, have been determined 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. [References: 20]