Physical Chemistry

V. V. Aleksandrov and Yu. A. Ershov

The Free Energy of KJ in Ethanol and Acetone

(Presented by Academician V. N. Kondrat’ev, January 22, 1960)

The free energy of solvation of KJ ($A_x$) in ethyl alcohol can be calculated (^1) from the value of the e.m.f. of a cell with transference. But this calculation method contains an error, since it is difficult to take into account the diffusion and interphase jumps of potential. Data on the magnitude of $A_x$ for KJ in acetone, as well as for other salts, are not available.

In the present work, to determine the free energy of solvation of KJ in ethyl alcohol and acetone, we used a cell without transference

[
(\mathrm{Hg})\mathrm{K}\,|\,\text{solution KJ}\,|\,\mathrm{AgJ},\ \mathrm{Ag}.
]

Experimentally this cell was realized by us in the form of the cell shown in Fig. 1. The design of the cell provides for regulation, within known limits, of the hydrogen pressure in the vessel with the initial amalgam, reliable isolation of the amalgam consumed during the measurement, and replacement of the capillary. Potassium amalgam and silver iodide electrodes were prepared as described in works (^2,^3). The solvents used and KJ were prepared by purification of commercial chemically pure products and, in their physical properties, corresponded to literature data. Measurement of the e.m.f. was carried out with a potentiometer of type R-375 at 25°. During measurements, dry, thoroughly purified hydrogen was continuously bubbled through the KJ solution. The results of the measurements—

Fig. 1. Electrolytic cell for measuring e.m.f. 1 — capillary of the amalgam electrode; 2 — silver iodide electrode; 3 — inlet of hydrogen into the solution; 4 — outlet of hydrogen; 5 — vessel with the solution under investigation (solution volume 35 ml); 6 — vessel for collecting the spent amalgam; 7 — vessel with the initial amalgam

Table 1

E.m.f. of the cell $(\mathrm{Hg})\mathrm{K}|\text{solution KJ}|\mathrm{AgJ},\ \mathrm{Ag}$ at various concentrations of KJ

the emf of the cell ((\mathrm{Hg})\mathrm{K}|\text{solution } \mathrm{KJ}|\mathrm{AgJ}, \mathrm{Ag}) at various concentrations of KJ in water, ethanol, and acetone are given in Table 1.

By the commonly used graphical extrapolation method ((^4)), we obtained values of the normal potentials ((E_0)) of the indicated cell in the specified solvents (in water, (E_0) was obtained by calculation from the measured emf and the values of the activity coefficients ((^5))). The values of (E_0) are given in Table 2.

Table 2

Free energy of solvation of KJ in solvents

* According to data from (1).

From the difference in the normal potentials of one and the same cell without transference in water and in a nonaqueous solvent, it is easy to calculate the difference in the free energies of solvation of KJ in (\mathrm{H_2O}) and in this solvent. Taking the free energy of hydration of KJ to be 137.4 kcal/mol ((^2)), from the differences determined by us in the solvation energies in water and ethanol, and in water and acetone, we calculated the free energies of solvation of KJ in these solvents. The corresponding values are given in Table 2.

The value (A) for KJ in ethanol, calculated from the emf of the cell with transference ((^1)), is equal to 131.5 kcal/mol. It should be noted that the change in the free energy of solvation of KJ on going from (\mathrm{H_2O}) to ethanol and acetone is parallel to the change in this quantity for HCl in the same solvents.

Institute of Chemical Physics
Academy of Sciences of the USSR

Kharkov State University
named after A. M. Gorky

Received
19 II 1960

CITED LITERATURE

1. N. A. Izmailov, Electrochemistry of Solutions, Kharkov, 1959.
2. B. P. Nikol’skii, M. Zakharevskii et al., Collection of Practical Works in Physical Chemistry, issue 1, Leningrad, 1951.
3. V. V. Owen, J. Am. Chem. Soc., 57, 1526 (1946).
4. N. A. Izmailov, V. V. Aleksandrov, ZhFKh, 31, 2619 (1957).
5. G. Harned, B. Owen, Physical Chemistry of Electrolyte Solutions, IL, 1952, p. 524.