Ion association in solutions of HCl in DMSO–water mixtures: ultrasonic absorption studies

Abstract

Ultrasonic absorption measurements are reported for the System HCl–dimethylsulfoxide (DMSO)–water in the frequency range 3.5 to 140 MHz. For ail solutions studied, the excess absorption due to the presence of HCl can be fitted well with a single relaxation equation. For 0.10 mol ℓ−1 solutions of HCl in DMSO–water mixtures, no further relaxations at higher frequencies are likely. Reasonable results are obtained when the ultrasonic results are analyzed assuming the process responsible for the excess absorption to be the dissociation–association equilibrium of HCl, and using equilibrium constants determined from conductivity (C. Cooke etal. Electrochim. Acta, 20, 591 (1975)). The value of |ΔVeff| is 20–25 cm3 mol−1 and Kass is approximately 3 × 109ℓ mol−1 s−1, as compared to a value of 10 × 109ℓ mol−1 s−1 calculated from limiting conductivities assuming diffusion-controlled rate theory.