pH‐Measurements in alcohol‐water mixtures, using aqueous standard buffer solutions for calibration

Abstract

Abstract E.m.f.‐measurements on cells of the type: Hg/Hg 2 Cl 2 /saturated KCl‐soln. (aq.)/standard buffer soln./saturated KCl‐soln.(aq.)/Hg 2 Cl 2 /Hg, using standard buffer solutions in methanol‐water and ethanol‐water mixtures and liquid‐junction forming devices of different design, showed that, for three different boundary‐types, the liquid‐junction potentials are identical within experimental error. E.m.f.‐measurements on cells of the type: glass electrode/standard buffer soln./saturated KCl‐soln.(aq.)/Hg 2 Cl 2 ‐Hg, using succinate standard buffer solutions in methanol‐water and ethanol‐water mixtures and different types of glass electrodes, proved that the variation of the standard potential of these glass electrodes with the composition of the alcohol‐water mixture does not depend on the type of glass electrode. These results, together with the previously shown fact, that liquid‐junction potentials at the boundaries standard buffer soln. (alcohol‐water)/saturated KCl‐soln.(aq.) are independent of the nature of the buffering solute, render possible the determination of pa*H‐values of solutions in alcohol‐water mixtures by calibration of a pH‐meter with the aid of an aqueous standard buffer solution and correction of the pH‐readings with a correction term δ. For a number of methanol‐water and ethanol‐water mixtures δ‐values are tabulated and graphs, showing the variation of δ with methanol‐ and ethanol‐percentage, are given.