Conductivity Measurements of Alkali Metal Thiocyanates in Water-Methanol Mixtures

Abstract

The conductivity of several alkali metal thiocyanates in water-methanol mixtures was measured at 25°C. The data were analyzed using the Lee-Wheaton theory for symmetrical electrolytes to obtain ion association constant, K_A, limiting molar conductivity, Δ₀, and limiting ionic molar conductivity, λ₀^±. In all the solvent systems, calculated λ₀⁺ values of the alkali metal ions increase in the order Li⁺<Na⁺<K⁺<Rb⁺<Cs⁺. The.λ₀^± values of the alkali metal ions and thiocyanate ion showed a minimum whe n the molar fraction of methanol was ca.0.4. The changes in λ₀^± of these alkali metal ions and thiocyanate ion with the molar fraction of methanol agree with the change in the viscosity of the solvent or the heat of mixing of water-methanol mixtures. These alkali metal thiocyanates form little or no ion aggregated in water and water-methanol mixtures. These alkali metal thiocyanates were K_A=15-24 dm3 mol^-1 in methanol.