Medium Effects and Determination of Primary and Secondary Standards for pH Measurements in (Glycerol + Water) Solvent Media at Normal and Subzero Temperatures, With Characterization of Appropriate Salt Bridges

The primary and the secondary standards for the pH measurements in solvent media Z = (glycerol [G] + water [W]) at glycerol mass fractions w G up to 0.4 and at temperatures from −10 °C to +40 °C have been determined in compliance with the IUPAC criteria. To this purpose, Harned’s reversible cell {Pt|H2|Primary Buffer + KCl in Z|AgCl|Ag|Pt} and Baucke’s nonreversible cell {Pt|H2|Buffer at pHPS in Z|Salt Bridge in Z|Buffer at pHSS in Z|H2|Pt} were used, respectively. As a result, three primary standards (based on the “carbonate”, the “equimolal phosphate”, and the “phthalate” buffers) and three secondary standards (based on the “tetroxalate”, the “tartrate”, and the “unequimolal phosphate” buffers) are now available. Their internal consistency was ascertained through the linear pH dependence of the voltage of the cell {Pt|H2 |Buffer at pHPS [or pHSS] in Z|NH4Cl Bridge in Z|Reference Electrode}. These acquisitions enable the user to perform routine pHX measurements by the regular operational cell {Reference Electrode|Salt Bridge in Z|Sample at pHX or Standard at pHPS [or pHSS] in Z|Glass Electrode}, with preliminary calibration by the two-standard scheme or the multistandard scheme. As indispensable components to be selected for insertion in the above operational pH cell to abate the intervening liquid junction potentials, four salt bridges (NH4Cl, RbCl, CsCl, and KCl in Z) have been characterized by the transference cell method: the most appropriate and recommended of them is the saturated NH4Cl bridge. The comparability of pH scales in (glycerol + water) with the pH scale in pure water is discussed in terms of the relevant autoprotolysis constants pK AP for the scale widths and of the primary medium effects of the H+ transfer for the relative positions of zero-points of pH scales.