Verification of the approximate equitransference of the aqueous potassium chloride salt bridge at high concentrations

Use of chlorine electrodes in the transference cell Pt-Ir|Cl2|KCl aq, m2||KCl aq, m1|Cl2|Pt-Ir, whose emf. was measured at 298.15 K at various KCl molalities m2 with fixed m1, allowed the cation and the water transference nos., τK+ and τW, resp., to be detd. up to the KCl satn. molality. The obsd. τK+ and τW values are in good accord with the overall and single-ion primary-hydration nos. of KCl. It turns out that τK+ is substantially const. at 0.486 in the usual molality range employed for KCl as a salt bridge in electrochem. and electroanal. This imperfect equitransference of the popular, aq. KCl salt bridge causes imperfect efficacy of the latter in minimizing liq. junction potentials and may, in turn, enlarge the uncertainty limits of anal. results. It is, thereby, suggested that when high-ionic-strength, strongly acidic or strongly alk. samples are submitted to pH-metric, pion-metric, or titrimetric anal., the KCl salt bridge be replaced by the closely equitransferent (τCs+ = 0.502) CsCl salt bridge, whose satn. molality is, furthermore, as high as 11.3 mol kg-1 at 298.15 K.