Standard pH Values for the Potassium Hydrogen Phthalate Reference Buffer Solution from 0 to 60 °C

The standard pH values of the solution of potassium hydrogen phthalate (molality 0.05 mol kg−1) have been redetermined over the temperature range 0 to 60 °C, using SRM 185d. Extensive measurements were made of the emf of cells of the type Pd;H2(g,1atm)|KH phthalate(m=0.05),KCl(m)|AgCl;Agwhere mKCl was 0.015, 0.01, or 0.005 mol kg−1, from which values of the acidity function p(aHγCl) were derived. The pH convention defines γCl the range of ionic strengths 0 to 0.1 mol kg−1 and permits conventional values of paH be obtained. According to NBS procedures, paH for selected reference solutions is identified with the standard pH(S) in the operational definition of pH. The new values, given in terms of the thermodynamic temperature (T) by PH(S)=2073.44T−13.3270+0.045199T−3.4846×10−5T2differ, on the average, by 0.003 unit from the results based on the 1944 data of Hamer and Acree.