Consistency of pH standard values with the corresponding thermodynamic acid dissociation constants (Technical Report)

With the simplest possible assumptions on the ion activity coefficients, namely a Debye-Huckel approach, pH values of eleven standard buffer solutions have been calculated from the corresponding thermodynamic acidity constants, K(I-->0), and compared to the electrometrically assigned pH(S) values (by Hamed cell method). Agreement is within +/-0.01 in the temperature range 10-40 degrees C for all standards, except carbonate. The results for the phthalate, acetate, phosphate and carbonate systems at 25 degrees C indicate that this consistency is improved if specific ion interactions are taken into account, according to the Pitzer theory.