A compilation of heat
capacity, heat of dilution, and activity data for aqueous urea solutions is
made from published sources. The existing apparent volume data are supplemented
by new measurements at 0�, 40�, and 50�.
The thermodynamic data are interpreted in
terms of association models, and it is found that the use of Flory-Huggins statistics for the entropy of mixing of the
various associated species and the solvent gives a much better description than
mole-fraction statistics. Heats of association and equilibrium constants are
evaluated.
The conductances of sodium hydroxide solutions at 15', 2b0, 50°, and 75" have been determined at concentrations up to 0 . 0 2~ with special precautions to eliminate the effects of carbon dioxide and of alkaline attack on glass cells. The limiting conductances have been determined from the Fuoss-Onsager and Pitts equations, and the mobility of the hydroxide ion calculated. The theoretical specific conductance of water at various temperatures has been calculated.
The activity coefficients
of cadmium chloride in water and sodium chloride solution have been measured.
The data have been used to calculate the stability constants of the cadmium
chloride complexes. The results are compared with the results of previous work
and reasons for the discrepancies are suggested.
The diffusion of the monocarboxylic acids
formic, propionic, and n-butyric in aqueous solution at 25� over the range
0.06-2.00M is studied by the Gouy interferometric method. The results, together
with Vitagliano's and Lyons's results for acetic acid, are corrected to allow
for the effects of ionization. A treatment of the effects of molecular
association on the experimental diffusion coefficients is proposed, and applied
with moderate success to acetic acid, propionic acid, and n-butyric acid. Mobilities
of the undissociated acid molecules at infinite dilution are found to be
greater than the limiting mobilities of the corresponding anions. Association
constants of the monocarboxylic acids over the concentration range studied are
calculated from existing activity data.
The isothermal displacement
calorimeter described previously has been modified by the inclusion of a
thermoelectric cooling module to allow the study of both endothermic and
exothermic mixing. Other modifications are also described. Excess enthalpies
are reported for 1,4-dioxan+tetrachloro-methane, benzene+dichloromethane,
tetrahydrofuran+water, and ethanol+water at 298.15 K and 1,4- dioxan+dichloromethane
at 298.15 and 303.15 K. These mixtures have been suggested as possible
reference mixtures for either checking the operation of, or calibrating,
calorimeters to be used for making measurements on exothermic mixtures. The
performances of our calorimeters have been evaluated on the basis of the results
presented here and by comparison with previous results. Some advantages and
disadvantages of the proposed reference mixtures are discussed. Photochemical
effects from the tungsten thermostat lamp affect the results for mixtures of
tetra-chloromethane with 1,4-dioxan.
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