Characterization of potassium chloride as an equitransferent "intersolvental" salt bridge

The electromotive forces (emF) E-A and E-C of the following concentration c ells with transference: Ag/AgCl/KCl(m(2))parallel to KCl (m(1))\AgCl\Ag and KxHg1-x\KCl (m(1))parallel to KCl (m(2))\KxHg1-x, respectively, together w ith the emfs E-MAX of the corresponding double cell without transference: K xHg1-xKCl (m(1))\AgCl\Ag-Ag\AgCl\KCl (m(2))\KxHg1-x have been measured at K Cl molalities m (m(1) fixed and m(2) varied, with m(2) > m(1)) approximatel y up to the KCl solubility limit in 12 solvent mixtures for the three aqueo us-oganic solvent systems (ethylene glycol + water),(acetonitrile + water), and (1,4-dioxane + water) up to 0.8 mass fraction of organic component. Fo r all the cases explored, the E-A vs. E-MAX relation is linear over the who le KCI molality range. The ionic transference numbers tof KCI determined th erefrom show a curvilinear dependence on the mass fraction of the organic c omponent of the relevant solvent mixture and are found to fall in the range 0.52-0.48, viz, within +/-4% of exact equitransference (t(+) = t(-) = 0.5) . In particular, KCI becomes exactly equitransferent (i.e., an ideal salt b ridge) in aqueous mixtures with the following mass fractions of organic com ponent: 0.4 ethylene glycol and 0.09 acetonitrile, as well as 0.12 methanol , and 0.08 and 0.34 ethanol from our recent work. Even if use of KCI as a s alt bridge would be somewhat restricted by its limited solubility in high m ass fractions of dioxane and acetonitrile and pending extension of investig ation to other mixed-solvent systems, the above figures characterize KCI as a fairly good "intersolvental" salt bridge in electrochemistry, electroana lysis, and corrosion science.