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

Abstract

Seven standard solutions serve to fix the NBS conventional activity scalc of pH (termed pH.) from 0 to 95° C. The original emf data have been re-examined and t he valucs of the acidity function p (aaYC I), from which pH. is derived, have been recalculated with the usc 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. values to the third decimal have been assigned. Thcse "experimental" pH. valucs in the temperature range 0 to 95 °C have been smoothed as a function of temperature by lcast- squares treatment. The properties and uscs of t he standards are discussed and directions for the preparation of the solutions are given.