Properties of molten carboxylates. Part 1.—Electrical conductance and molar volumes of some molten lead and zinc carboxylates

Abstract

The temperature dependences of the molar volumes, densities and electric conductivities of molten lead and zinc carboxylates of even numbered chain length from C₆ to C₁₈ inclusive are reported at temperatures from the melting points to just below the decomposition points. The molar volumes are linear functions of chain length and nearly so of temperature within the interval of measurement. Semilogarithmic plots of specific conductivity against inverse temperature for the zinc soaps are linear and the slopes decrease slightly with increasing chain length, representing enthalpies of about 40 kJ mol^–1. A simple model for the system which proposes that the conduction is due to a small concentration of relatively mobile Zn²⁺ ions is presented. With the lead salts plots of log specific conductivity against inverse temperature show curvature. Attempts to fit the data to the equation κ=A exp[–C/(T–T₀)] showed non-random deviations. Instead, a dissociation equilibrium in the melt is proposed which reaches completion in the high temperature range. It is proposed that the major current carrier is the lead ion and values of about 15 kJ mol^–1 are found for its activation energy for mobility. An approximate method is used to estimate ΔH and ΔS for the proposed dissociation reaction from the conductivity data. They are found to be about 85 kJ mol^–1 and 190 J mol^–1 K^–1 respectively for all the compounds studied. The high entropy change may indicate considerable aggregation of the undissociated species in the melts.