Standard pH Values for Potassium Hydrogenphthalate Reference Buffer Solutions in 10, 30 and 50 wt per cent 1,4-Dioxane + Water Mixed Solvents at Temperatures from 288.15 to 318.15 K

Standard pH(S) values for 0.05 mol kg-1 potassium hydrogenphthalate (KHpH) reference buffer solutions in 10, 30 and 50% (w/w) 1,4-dioxane/water solvent mixtures within the temperature range 288.15-318.15 K are determined from e.m.f. measurements of the cell without transference Pt|H2|KHPh + KCl|AgCl|Ag|Pt. The consistency of the results is analysed by a recently described method of multilinear regression of the quantity p(aHγCl) as a function of both solution composition and temperature. The standard pH(S) determined can be reproduced to within ±0.01 by the equation pH(S) - 4.004 + 3.309w + 0.408z + 1.037w3 - 14.95zw2 + 27.1zw3, where w is the weight fraction of dioxane in the solvent mixture, z = (T - θ)/θ, and θ - 298.15 K. Values of the first ionization constant of phthalic acid (H2Ph; benzene-1,2-dicarboxylic acid) in the above solvent mixtures are also determined from e.m.f. measurements of the cell without transference Pt|H2|H2Ph + KHPh + KCl|AgCl|Ag|Pt.