Unusual behavior of the conductivity of LiNO3 in tert-butanol: ion clustering or ion-pair aggregation

Abstract

The electrical conductance of LiNO3 in tert-butanol–water mixed solvents changes gradually from "normal" in pure water to "abnormal" in pure tert-butanol. In water the measured specific conductance increases with increase of temperature, and in tert-butanol the conductance decreases with increase of temperature. In pure tert-butanol, the electrical conductances of NH4ClO4 and LiClO4 increase with the salt concentration and temperature at lower temperatures, but decrease at higher temperatures. The molar conductivity Λ0(10−4 S m2 mol−1) in tert-butanol at 300 K is 5.0 for NH4ClO4 and 4.0 for LiClO4. Both activation energies EΛ0 are 17 kJ mol−1, which gives an unusual correlation between Λ0 and viscosity η(mPa s): [Formula: see text] The values of Λ0 for NH4NO3 and LiNO3 in tert-butanol could not be measured, because ion aggregation is significant even at the lowest concentrations required to obtain conductances sufficiently above that of the solvent. The measured temperature coefficient of LiNO3 conductance in tert-butanol is negative. Ion clustering of nitrate salts is attributed to poor solvation of the planar NO3− ions by the globular tert-butanol molecules. Ion aggregation in tert-butanol increases with increasing T, due to the relatively rapid decrease of the value of εT. Corrections are listed for reaction kinetics parameters for nitrate salts in pure tert-butanol solvent reported in Can. J. Chem. 73, 392 (1995). Keywords: tert-butanol, ion-pair aggregation, lithium nitrate, electrical conductance, solvent effects.