Characterization of Lithium Sulfate as an Unsymmetrical-Valence Salt Bridge for the Minimization of Liquid Junction Potentials in Aqueous−Organic Solvent Mixtures

Abstract

The transference numbers t of lithium sulfate in acetonitrile/water and methanol/water solvent mixtures have been studied by measuring the emfs of such transference cells as Pb(Hg)|PbSO(4)|Li(2)SO(4) (m(2))||Li(2)SO(4) (m(1))|PbSO(4)| Pb(Hg), Hg|Hg(2)SO(4)|Li(2)SO(4) (m(2))||Li(2)SO(4) (m(1))|Hg(2)SO(4)|Hg, and Li(x)Hg(1-)(x)|Li(2)SO(4) (m(1))||Li(2)SO(4) (m(2))|Li(x)Hg(1-)(x), in view of characterizing Li(2)SO(4) as an unsymmetrical salt bridge for the minimization of liquid junction potentials in potentiometric applications. In water, Li(2)SO(4) is nearly as good a salt bridge as the popular KCl one. Its effectiveness has been verified through the operational pH-metric cell using various aqueous pH(S) standards. In acetonitrile/water solvents of 0.09 mass fraction of acetonitrile at 298.15 K, Li(2)SO(4) shows exact ionic equitransference, obeying the general condition t(+)/z(+) = t(-)/|z(-)|. The Li(2)SO(4) salt bridge can be used either for simple insertion between two different electrolyte solutions to minimize the intervening liquid junction potentials, as the outer component of a double-bridge arrangement of any commonly available reference electrode, or, obviously, for structural incorporation in sulfate-reversible reference electrodes as the appropriate supporting and bridge electrolyte. The operational potential of the Hg| Hg(2)SO(4)|2 m Li(2)SO(4) reference electrode in aqueous solutions is 0.6326 V at 298.15 K.

Ligand‐Exchange Processes on Solvated Lithium Cations: Acetonitrile and Hydrogen Cyanide

“…[36] Over the past decade, DFT and ab initio calculations on [Li(CH 3 CN) n ] + and related clusters were also performed by different groups. [30,[37][38][39][40] There has been a special interest in the properties of Li salts, such as conductivity, [41][42][43][44] transport abililty, [45][46][47] viscosity, [48] and osmotic behaviour [49] , in solvents and solvent mixtures because of the use of Li + ions in batteries of high energy density. [50] Such studies are not restricted to liquid systems.…”

Sulfate-sensing electrodes. The lead- amalgam/lead-sulfate electrode (IUPAC Technical Report)

“…Obviously, a prerequisite is the availability of appropriate SO 4 2--based salt bridges. This unsymmetrical salt bridge does exist: it is a concentrated Li 2 SO 4 solution, as it has been recently proven by Faverio and Mussini [5]. As it was pointed out earlier by Mussini [6], any binary (z + : z − )−valent salt used for minimizing liquid junction potentials must be "equitransferent".…”

“…None of the other alkali metal sulfates satisfies the above condition. Using a Li 2 SO 4 salt bridge of m = 2 mol·kg -1 (whose ionic strength is 6 mol·kg -1 , i.e., higher than that of the saturated KCl), Faverio, Mussini, and Mussini [5] found that the working potential of the mercury|mercurous-sulfate reference electrode is 0.6327 V at 25 °C, and that of the lead-amalgam|lead-sulfate treated here is −0.3327 V.…”

“…It was recently found [5] that Li 2 SO 4 is a good salt bridge also in aqueous-organic solvent mixtures, e.g., acetonitrile-water mixtures [5]. It is, therefore important, to extend the characterization and standardization of the lead-amalgam|lead-sulfate electrode to these mixed solvents.…”

“…However, it is necessary to consider a possibility of using lead-amalgam|lead-sulfate|SO 4 2-electrodes equipped with built-in sulfate-based salt bridges, in the context of the availability of proper alternative reference electrodes for general use. Indeed, Faverio and Mussini [5] …”