Isentropic compressibilities of some copper(I), sodium(I) and tetraalkylammonium salts evaluated from ultrasonic velocity measurements in acetonitrile + N,N-dimethylformamide mixtures at 298.15 K

Abstract

Ultrasonic velocity (u) and density (p) of tetrabutylammonium tetraphenylborate (Bu 4 NBPh 4 ), tetrabutylammonium perchlorate (Bu 4 NClO 4 ), copper(I) perchlorate tetraacetonitrile (CuClO 4 .4CH 3 CN), sodium perchlorate (NaClO 4 ) and sodium tetraphenylborate (NaBPh 4 ) have been measured at different salt concentrations in the concentration range 0.02-0.6 mol kg - 1 in binary mixtures of acetonitrile (AN) with N,N-dimethylformamide (DMF) containing 0, 10, 20, 40, 60, 75, 80, 90 and 100 mol % DMF. The isentropic compressibility (K s ) and apparent molal isentropic compressibility (K s , Φ ) of the salts in various solvent mixtures have been calculated. Limiting apparent molal isentropic compressibilities (K o s,Φ) for various salts have been evaluated and split into contributions of individual ions i.e. into (K o s,Φ) ′ values. The variation of (K o s,Φ) ′ values with solvent composition shows that Na + has very large negative (K o s,Φ) ′ values which show strong solvation of Na + in AN + DMF mixtures over the entire solvent composition range and the solvation of Na + by DMF is relatively stronger than that with AN. Cu + also shows strong but relatively less solvation as compared to Na + in AN + DMF mixtures over the entire solvent composition range. The solvation of Cu + by AN is relatively stronger than with DMF. ClO - 4 shows much weaker solvation in AN+DMF mixtures by having some interaction with AN in the AN rich region of the mixture.