Unified pH Measurements of Ethanol, Methanol, and Acetonitrile, and Their Mixtures with Water

Measurement of pH in aqueous-organic mixtures with different compositions is of high importance in science and technology, but it is, at the same time, challenging both from a conceptual and practical standpoint. A big part of the difficulty comes from the fundamental incomparability of conventional pH values between solvents (spH, solvent-specific scales). The recent introduction of the unified pH (pHabs) concept opens up the possibility of measuring pH, expressed as pHabsH2O, in a way that is comparable between solvent, and, thereby, removing the conceptual problem. However, practical issues remain. This work presents the experience of the authors with measuring pHabsH2O values in mixtures of methanol, ethanol, and acetonitrile, with water, but without the presence of buffers or other additives. The aim was to assigned pHabsH2O values to solvent–water mixtures using differential potentiometry and the ‘pHabs-ladder’ method. Measurements were made of the potential difference between glass electrodes immersed in different solutions, separated by an ionic liquid salt bridge. Data were acquired for a series of solutions of varying solvent content. This work includes experiences related to: a selection of commercial electrodes, purity of starting material, and comparability between laboratories. Ranges of pHabsH2O values for selected compositions of solvent–water mixtures are presented.

Thermal conductivity of salt-bearing ice analogs in Jovian moons to support future JUICE mission.

<p>Thermal properties of frozen salt solutions are crucial to interpret the JUpiter ICy moons Explorer (JUICE) (ESA) and Europa Clipper (NASA) missions, which will be launched in the upcoming years to make detailed observations of the giant gaseous planet Jupiter and three of its largest moons (Ganymede, Callisto, and Europa) due to the scarcity of experimental measurements.</p> <p>Therefore, we have conducted a set of experiments to measure and study the thermal conductivity and calorimetry of macroscopic frozen salt solutions of particular interest in these regions, including Na-chloride (NaCl), Mg-sulphate (MgSO<sub>4</sub>), sodium sulphate (Na<sub>2</sub>SO<sub>4</sub>), and Magnesium chloride (MgCl<sub>2</sub>). A climatic chamber has been used to mimic the cryogenic conditions in the Jovian Icy Moons. Measurements were performed at atmospheric pressure and temperatures from 0 to -70ºC. Temperature and thermal conductivity were measured during the course of the experiments. A side effect of these measurements is that they served to spot phase changes in the ice mixtures. A small sample of the liquid salt-water solution was set aside for the calorimetry measurements.</p> <p>These experiments and the measurements of thermal conductivity and calorimetry will be valuable to constrain the chemical composition, physical state, and temperature of the upper layers of the icy crusts of Ganymede, Callisto, and Europa (please see abstracts EPSC Muñoz Iglesias et al. 2020 and EPSC Solomonidou et al. 2020).</p>