A STUDY OF ION-SOLVENT INTERACTION OF SOME TETRAALKYLAMMONIUM AND COMMON IONS IN N-METHYLACETAMIDE FROM APPARENT MOLAL VOLUME DATA

The apparent molal volumes, φv - s, of six tetraalkylammonium iodides, namely, Et4NI to Hep4NI, have been determined in N-methylacetamide (NMA), at different temperatures and concentrations from which the limiting apparent molal volumes, φv° - s, have been obtained for these salts. The results indicate that the φv vs. √c curves are almost straight lines for all the salts in the concentration range studied here. The curves for Et4NI and Pr4NI salts have a positive slope, and those for Bu4NI, Pen4NI, Hex4NI, and Hep4NI have a negative slope. Also φv° of the R4N iodides increases with the rise in temperature; however, dφv°/dt decreases with the rise in temperature for the smaller R4N iodides, while it remains almost temperature independent for the larger R4N iodides. Common electrolytes behave more or less like the smaller R4N iodides although dφv°/dt even becomes negative in these cases. An attempt has been made to explain these results from the point of view of electrostatic solvation and electrostriction in the case of smaller R4N+ ions and from the penetration and the relative volume effects for the larger R4N+ ions.