Abstract: pHstandard reference values, pH(RVS), for 0. 05 mol/kg potassium hydrogen phthalate buffer solutions in 10%, 14. 93% and 20% isopropanol+ water mixed solvents at temperatures from 278. 15 to 318. 15 Kare determined from reversible electromotive potential measurements of the cell without a liquid junction. On the basis of Pitzer's theory, a new method for determining the activity coefficients of each ion in the solutions is proposed. The second thermodynamic dissociation constants of v-phthalic acid are calculated, and the thermodynamic quantities of the second dissociation are calculated and the results are discussed.

Key words: Standard pH reference values. Potassium hydrogenphthalate, Isopropanol. Dissociation constant, Thermodynamics of dissociation