ELECTROLYTE-SOLVENT INTERACTION .19. SOLVATION BY MOLECULAR PICRIC ACID

The conductances in acetonitrile at 25° of solutions of tetrabutylammonium picrate and tetramethylammonium picrate and tetramethylammonium bromide to which picric acid was added have been measured. The conductance of the salts is decreased by the picric acid. If a specific preferential solvation of the anions by picric acid molecules, to give a complex with lower mobility, is assumed, the data can be quantitatively described in terms of an equilibrium between ions solvated by picric acid and ions surrounded only by acetonitrile. In purifying the acetonitrile, it was found that traces of ammonia can give spurious conductances for picric acid solutions, due to formation of ammonium picrate. For ammonium picrate in acetonitrile, the limiting conductance is 174.4 and the association constant is 185. A 1-ppm concentration of ammonia in acetonitrile of conductance of the order of 10-8 gives a specific conductance of 1.5 × 10-5 upon addition of picric acid.