A Determination of Standard Potentials and Related Primary pH Standards in the 50 Mass Percent (N-Methyl-2-Pyrrolidinone + Water) Mixture at Various Temperatures

Following the IUPAC-endorsed procedure, the primary pH standards offered by the equimolal phosphate buffer (Na₂HPO₄ (0.01 mol⋅kg⁻¹) + KH₂PO₄ (0.01 mol⋅kg⁻¹)) in the (N-methyl-2-pyrrolidinone + water) solvent mixture of 50 mass percent composition at various temperatures have been determined from potential difference measurements with the reversible Harned cell. Since the essential prerequisite of the above procedure is the knowledge of the (hitherto unknown) standard potential difference of Harned’s cell, a parallel supplementary series of potential difference measurements has been carried out with the reversible cell, Pt|H₂|HCl(m)|AgCl|Ag|Pt according to the classical thermodynamic procedure. The problem of comparability of the pH scale in the (N-methyl-2-pyrrolidinone + water) solvent with that in the pure water solvent is duly discussed in terms of primary medium effects.