Standard pH values for the potassium hydrogen phthalate reference buffer solution from 0 to 60°C

Abstract

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 $\text{Pd};{\mathrm{H}}_2\left(\mathrm{g},1\text{atm}\right)|\text{KH phthalate}\left(m=0.05\right),\text{KCl}\left(m\right)|\text{AgCl};\text{Ag}$where m_KCl was 0.015, 0.01, or 0.005 mol kg⁻¹, from which values of the acidity function p(a_Hγ_Cl) were derived. The pH convention defines γ_Cl the range of ionic strengths 0 to 0.1 mol kg⁻¹ and permits conventional values of pa_H be obtained. According to NBS procedures, pa_H 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 $\text{PH}\left(\mathrm{S}\right)=\frac{2073.44}{T}-13.3270+0.045199T-3.4846\times {10}^{-5}{T}^2$differ, on the average, by 0.003 unit from the results based on the 1944 data of Hamer and Acree.