Characterization of aqueous rubidium chloride as an equitransferent ultraconcentrated salt bridge

1998

Anal. Chem.

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.

mentioning

confidence: 99%

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

Faverio

1998

Anal. Chem.

“…For further practical comparison, note that in formamide equals in water; therefore, NH 4 Cl, NH 4 Br, and NH 4 I can act as salt bridges in formamide, whereas KCl cannot. Also inadequate in formamide are RbCl and CsCl, which were known to be the best salt bridges in water ever found. , The unique equitransference features in formamide offered by the ammonium halides in comparison with the other alkali halides can also be eloquently visualized by plotting the limiting cationic transference numbers against the pertinent Pauling's crystallographic ionic radii, r M + , as shown in Figure . The singularly higher transference number presented in formamide by the NH 4 + ion with respect to Rb + and K + , despite their nearly equal crystallographic radii, can only be explained by the mobility of NH 4 + being particularly enhanced by an ionic motion mechanism linked with the reciprocal favorable structures of ammonium and formamide.…”

Section: Resultsmentioning

confidence: 99%

Determination of Primary and Secondary Standards and Characterization of Appropriate Salt Bridges for pH Measurements in Formamide

Falciola

et al. 2003

Anal. Chem.

For the first time, the standardization for pH measurements is here implemented in the domain of superpermittive media. The nonaqueous solvent studied is formamide (epsilon = 109.5 at 298.15 K) for which three primary standards and two secondary standards have been determined, whose excellent internal consistency has also been demonstrated by specific cell measurements. A comparison of the pH scale in formamide with the aqueous scale has been duly tried by accounting for the primary medium effect on the H+ ion. Furthermore, as a result of an ad hoc supplementary systematic investigation, three salt bridges of appropriate level of equitransference in formamide, that is, NH(4)Cl, NH(4)Br, and NH(4)I, have been characterized for abating the liquid junction potentials intervening in the pH-measuring cell to enable the user to carry out regular pH measurements and related controls.

“…For such measurements to be reliable, it is well-known that the following four basic conditions must be complied with when measuring the emf's of the operational cell on the sample solution and on the standard reference solution: same temperature, same electrode pair, same salt bridge, and same solvent. For the case of working in purely aqueous solutions, a wealth of salt bridges (all of them definitely superior to the popular KCl) have been recently characterized (Mussini et al, 1990b;Mussini et al, 1993;Buizza et al, 1996) and are available for use, CsCl and RbCl being those that most closely approach the behavior of an ideal salt bridge.…”

Section: Introductionmentioning

confidence: 99%

“…Robinson and Stokes,1965b. b Longhi et al,1990c Buizza et al,1996 Interpolated fromLongsworth and MacInnes,1939. …”

mentioning

confidence: 99%

Transference Numbers of Alkali Chlorides and Characterization of Salt Bridges for Use in Methanol + Water Mixed Solvents

Basili

et al. 1999

J. Chem. Eng. Data

Electromotive force measurements at 25 °C of the transference cells Ag|AgCl|MeCl (m 2)|MeCl (m 1)|AgCl|Ag and Me x Hg1 - x |MeCl (m 1)|MeCl (m 2)|Me x Hg1 - x (where Me = Li, Na, K, and Rb and Me x Hg1 - x denotes a flowing Me-amalgam electrode at Me mole fraction x) have been made at various molalities m 2 > m 1 (with m 1 fixed and m 2 varied) in methanol + water solvent mixtures with methanol mass fractions w M up to 0.8. Supplementary emf measurements have been made of the cell Pt|Li x Hg1 - x |LiCl (m 1)|AgCl|Ag|Pt to obtain the required activity coefficients for LiCl at methanol mass fractions w M = 0.2. The general trend of the ionic transference numbers of each MeCl is a t°Me + increase with w M, which is much more pronounced for those Me+'s whose primary hydration sheaths are bigger (namely, Li+ and Na+). In particular, KCl becomes exactly equitransferent (t°K + = t°Cl − = 0.5, i.e. an ideal salt bridge) at w M ≈ 0.1, but at w M > 0.6 the KCl solubility becomes insufficient for a salt bridge function. The same drawback occurs also for RbCl, which is known to be the most closely equitransferent salt in water (t°Rb + = 0.5007). NaCl, which is quite unproposable as a salt bridge in water, may be useful at high methanol concentrations, as its ionic transference numbers would approach 0.5 at w M ≥ 0.8.