Transference Numbers of NaCl in Aqueous Mixtures with Organic Solvents of Moderate to Low Permittivities

Abstract

Electromotive forces (emf) were measured in the transference cells: Ag∣AgCl∣- Nacl (m2) in Z∥ NaCl (m1) in Z∣AgCl∣Ag and NaxHg1-x∣NaCl (m1) in Z∥ NaCl (m2) in Z∣NaxHg1-x (where NaxHg1-x denotes a flowing Na–amalgam electrode and Z an aqueous-organic solvent mixture) at various molalities m2 > m1 of NaCl in Z = (ethylene glycol + water), (acetonitrile + water) and (1,4-dioxane + water), with mass fractions of the organic components ≤0.8. The transference number of Na+ in (ethylene glycol + water) and (1,4-dioxane + water) varies little with respect to that in pure water medium, whereas in (acetonitrile + water) it increases remarkably with increasing proportion of acetonitrile so as to approach equitransference, behavior similar to that previously found in (methanol + water) and in (ethanol + water). At acetonitrile mass fraction 0.6 NaCl is sufficiently close to equitransference to emerge as a useful salt bridge, nearly at the same level as the popular aqueous KCl.