Salting-Out and Ionic Volume Behavior of Some Tetraalkylammonium Salts

Measurements of salting-out of Ar by NH(4)Br and a series of homologous symmetrical tetraalkylammonium bromides in water are reported and discussed. A new gas-solubility apparatus is used enabling the solubility to be derived from a number of measurements on the same gas-solution sample at various pressures, rather than from a single measurement on each solution. Unexpectedly large salting-out effects are observed which increase with cation size. Electrostatic and nonelectrostatic effects are examined in relation to the ionic-volume behavior in water and methanol as a basis for discussion of the results. The relative electrostrictions of the TAA and Br(-) ions in these two solvents are compared. Calculations based on electrostatic and scaled particle theory are compared, and it is concluded that the latter treatment obscures the electrochemical factors of essential interest in solute/solvent distribution about ions in solution.