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 stds. 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 mixt. of 50 mass percent compn. at various temps. have been detd. from p.d. measurements with the reversible Harned cell. Since the essential prerequisite of the above procedure is the knowledge of the (hitherto unknown) std. p.d. of Harned's cell, a parallel supplementary series of p.d. measurements has been carried out with the reversible cell, Pt|H2|HCl(m)|AgCl|Ag|Pt according to the classical thermodn. 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.