Revised standard values for pH measurements from 0 to 95 °C

Abstract

Seven standard solutions serve to fix the NBS conventional activity scale of pH (termed pH_s) from 0 to 95° C. The original emf data have been re-examined and the values of the acidity function p(α_Hγ_Cl), from which pH_s is derived, have been recalculated with the use of a single consistent set of standard potentials and electrochemical constants. The convention proposed recently by Bates and Guggenheim for the numerical evaluation of the individual activity coefficient of chloride ion in the buffer solutions has been adopted, and by this means pH_s values to the third decimal have been assigned. These “experimentar” pH_s values in the temperature range 0 to 95 °C have been smoothed as a function of temperature by least-squares treatment. The properties and uses of the standards are discussed and directions for the preparation of the solutions are given.