Proton transfer conductance in aqueous solution. Part 1.—Conductance of concentrated aqueous alkali metal hydroxide solutions at elevated temperatures and pressures

Abstract

Measurements of the electrical conductivity of aqueous solutions of KOH, NaOH and LiOH are presented within the ranges 25–200°C, 1–3000 atm and 0.1–6.68 molal. These indicate that with increasing concentration there is a transition in the primary mechanism of conductance in these solutions from the proton transfer mechanism to the hydrodynamic mechanism. In LiOH solutions, however, saturation occurs before this transition is established. It is suggested that at high concentrations most of the water molecules are dominated by their proximity to an ion and so cannot participate in the proton transfer mechanism of conductance by the hydroxyl ion. This mechanism is disrupted most by KOH and least by LiOH at a given concentration in excess of 1 molal, and this is related to the greater ionic association of the latter solute. With increasing concentration of KOH the Walden product becomes more nearly independent of temperature and pressure. Data for the viscosity of water have been surveyed and a table covering the ranges 10–200° and 1–3000 kg cm^–1 is presented. The pressure dependence of the conductance of these solutions is virtually independent of concentration to the unexpectedly high value of about 1 molal, but it alters markedly in the range 1–2 molal. The observations are discussed qualitatively.