Limiting Conductivities and Ion Association in Aqueous NaCF3SO3 and Sr(CF3SO3)2 from (298 to 623) K at 20 MPa. Is Triflate a Non-Complexing Anion in High-Temperature Water?

Abstract

Frequency-dependent electrical conductivities of solutions of aqueous sodium trifluoromethanesulfonate (“triflate”) and strontium triflate have been measured from T = 298 K to T = 623 K at p = 20 MPa, over a very wide range of ionic strength [(2·10–5 to 0.35) mol·kg–1], using a unique high-precision flow-through AC electrical conductance instrument. Experimental values for the equivalent conductivity, Λ, of each electrolyte were used to calculate their equivalent conductivities at infinite dilution, Λ°, with the Turq–Blum–Bernard–Kunz (TBBK) ionic conductivity model. Values were derived for the limiting equivalent conductivity of the triflate ion, λ°(CF3SO3–), and the strontium ion, λ°(Sr2+). The TBBK fits to the concentration-dependent equivalent conductivity data for both NaCF3SO3 and Sr(CF3SO3)2 required statistically significant ionic association constants for the species NaCF3SO30 at temperatures T > 448 K, SrCF3SO3+ at T > 448 K, and for Sr(CF3SO3)20 at T > 548 K. The stepwise association constants,...