Electromotive force measurements at 25 °C of the transference cells Ag|AgCl|MeCl (m2)|MeCl (m1)|AgCl|Ag and MexHg1-xjMeCl (m1)|MeCl (m2)|MexHg1-x (where Me ) Li, Na, K, and Rb and MexHg1-x denotes a flowing Me-amalgam electrode at Me mole fraction x) have been made at various molalities m2 > m1 (with m1 fixed and m2 varied) in methanol + water solvent mixtures with methanol mass fractions wM up to 0.8. Supplementary emf measurements have been made of the cell Pt|LixHg1-x|LiCl (m1)|AgCl|Ag|Pt to obtain the required activity coefficients for LiCl at methanol mass fractions wM = 0.2. The general trend of the ionic transference numbers of each MeCl is a t°Me+ increase with wM, 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 wM around 0.1, but at wM > 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 wM g 0.8.
|Titolo:||Transference numbers of alkali chlorides and characterisation of salt bridges for use in methanol + water mixed solvent|
MUSSINI, TORQUATO (Secondo)
VERTOVA, ALBERTO (Ultimo)
|Settore Scientifico Disciplinare:||Settore CHIM/02 - Chimica Fisica|
|Data di pubblicazione:||ott-1999|
|Digital Object Identifier (DOI):||10.1021/je9900979|
|Appare nelle tipologie:||01 - Articolo su periodico|