Effect of Sodium Monocarboxylate on
Water by 1P-Probing Methodology II

In 1P-Probing Methodology (1P: 1-propanol), excess partial molar enthalpies of 1P, HE1P = ∂HE/∂n1P, for the 1P – S – H2O (S: sodium monocarboxylates CnH2n+1COONa (n = 0, 1, 2)) ternary systems were measured with an isoperibol titration calorimeter and their concentration derivatives, HE1P–1P = N(∂HE1P/∂n1P) = (1 - x1P)(∂HE1P/∂x1P), were calculated. From the concentration dependences of the HE1P–1P’s of CnH2n+1COONa, it was suggested experimentally that the hydrophobicity of monocarboxylate anions is strengthened as n is increased. The hydration numbers of HCOO−, CH3COO−, and C2H5COO− were estimated to be 1.2, 3.7, and 9.0, respectively.

(by T. Kondo, Y. Miyazaki & Y. Koga)

Fig. 1 Concentration dependence of HE1P and HE1P–1P for CH3COONa.

Fig. 2 Concentration dependence of HE1P and HE1P–1P for C2H5COONa.

Fig. 3 Concentration dependence of HE1P and HE1P–1P for HCOONa.

Fig. 4 Initial concentrations of aqueous solutions of sodium monocarboxylates vs. values of x1P of point X. Broken line shows the contribution of a Na+ ion.