Conductance of potassium lodide in mixed solvents

Abstract

The conductance of potassium iodide has been measured in the solvents ethylene carbonate, water, methyl ethyl ketone, and pairwise mixtures of these solvents at 40°C; and ethylene carbonate-water, tetramethylene sulfone-water, dimethyl sulfoxide-water, tetrahydrofuran-water, ethylene carbonate-tetramethylene sulfone-water, ethylene carbonate-tetramethylene sulfone, and tetrahydrofuran-dimethyl sulfoxide at 25°C. For dielectric constants greater than about 60, the pairing constants K_A are in the range 0.3–2.0; no correlation between K_A and solvent properties could be established. For lower dielectric constants, K_A increases exponentially with decreasing dielectric constant. Addition of a proton, acceptor to water initially decreases K_A regardless of whether the dielectric constant of the mixture is higher or lower than that of water, suggesting that ion pairs in water may be stabilized by cage structures. The Walden product A_oη is also decreased by the addition of proton acceptors.