The apparent molal volumes, φv's, of (0.05 m) NH4Cl, Me4NCl, Et4NCl, n-Pr4NCl, and n-Bu4NCl have been determined at one-degree intervals from 20 to 40° from precision density measurements. The apparent molal expansibilities, φE's, have been calculated from the φv values at various temperatures and have been equated to the infinite dilution molal expansibility, Ē0. The Ē0 values of the R4NCl's are not a linear function of molecular weight of the cation, R4N+. The Ē0 of NH4Cl is low, apparently due to the ability of the NH4+ ion to form an "icelike" species in solution. The Ē0's of Pr4NCl and Bu4NCl appear to be high compared to the lower molecular weight R4NCPs. This nonlinear behavior is interpreted as being due to expansibility changes in the structure of water caused by the R4N+ cations, Ē0(struct). This structural effect decreases as the temperature increases and increases as the size of R4N+ increases. The similarity of V̄0 properties of R4N+ cations and the aliphatic alcohols is discussed, and it is postulated that the abnormal properties of R4N+ salts may be normal for solutes able to cause hydrophobic bonding.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry