Apparent molal volumes and heat capacities of some alkali halides and tetraalkylammonium bromides in aqueoustert-butanol solutions

The densities and volumetric specific heats of hydrochloric acid, alkali chlorides and bromides, and tetraalkylammonium bromides were measured in 0 to 40% by weighttert-butanol (t-BuOH) in water with a flow densimeter and a flow microcalorimeter. The effect of salt concentration was investigated in the case of NaCl. The apparent molal volumes and heat capacities and the derived transfer functions of the electrolytes from water tot-BuOH-water mixtures can be interpreted through solute-solute pair and triplet interactions by analogy with the transfer functions oft-BuOH from water to electrolyte solutions, with the salting-in and salting-out effects, and with the influence of electrolytes on the thermodynamics of micellization. At lowt-BuOH concentrations, the transfer functions seem to be reflecting primarily electrolyte-nonelectrolyte pair interactions. At intermediatet-BuOH concentration, wheret-BuOH associates, the hydrophobic bonding is enhanced by hydrophilic ions through a salting-out effect on monomers and by hydrophobic salts through triplet interaction (mixed association complexes). The Me ₄ NBr and Et ₄ NBr are intermediate electrolytes which do not have much effect on thet-BuOH hydrophobic bonding. At hight-BuOH concentrations the transfer functions tend to the values they would have in puret-BuOH.