ON T H E ELECTRICAL CONDUCTIVITY O P SOLUTIONS I N ETHYL AMINE B Y FREDERICK I,.
SHINN
Some years ago Kahlenberg and Ruhoffl published the results of some measurements of the electrical conductivity. of solutions in amyl amine. The salts employed as solutes were silver nitrate, cadmium iodide, and ferric chloride. It was shown that these solutions afford striking examples of the phenomenon of the diminution of the so-called molecular conductivities upon increasing the dilution beyond a certain point. I n all cases the molecular conductivities were small and attained extremely low values at dilutions ranging from fifth- to eightieth-normal. More recently H. D. Gibbs,' in connection with a study of the solvent power of liquid methyl amine, has shown, in a qualitative way, that certain salts dissolved in that solvent yield very good conducting solutions, many of the solutions having specific resistances of less than IOO ohms. The specific conductivities, however, are much lower than for solutions in liquid a m m ~ n i aof, ~which methyl amine is the first homologue. On the other hand, solutions in liquid methyl amine are very much better conductors than solutions in amyl amine. It was therefore to be expected, in accordance with the general behavior of solvents which are members of a homologous series, that solutions in ethyl amine would show conductivities lying between those in liquid methyl amine and amyl amine. This was found t o be the case. The following salts were first rendered anhydrous and then examined as to their solubility in anhydrous ethyl amine. Many of them reacted with the solvent, forming insoluble or difficultly soluble residues. These precipitates were not
*
Jour. Phys. Chem., 7, 254 (1903). Jour. Am. Chem. SOC., 28, 1395 (1906). Franklin and Kraus: Am. Chem. Jour., 23, 277 (1900)
538
Frederick I,. Shinn
examined further, but they probably consist of addition products formed with ethyl amine. Very soluble with evolution of ammonia. Soluble. Slightly soluble. Insoluble, unchanged. Reacts with evolution of heat, forming greenish yellow precipitate. Reacts, forming white precipitate which afterward dissolves. Insoluble, unchanged. Slightly soluble. Reacts, forming white insoluble precipitate. Slightly soluble. Slightly soluble. Soluble, with evolution of much heat. Insoluble, unchanged. Reacts, forming white insoluble precipitate.
The ethyl amine was Schuchardt's preparation. It was allowed to stand over potassium hydroxide ,and was then distilled. The portion passing over between 18.4' and 19.4' C at 747 mm was used in the conductivity measurements. Its specific conductivity was of the order of 4 X IO-' at o o C. The conductivity measurements were carried out a t 0' C on account of the volatility of the solvent. The simple resistance cell used and described by Kahlenberg and Ruhoff was employed in connection with the usual (Kohlrausch) method. Few of the saits examined lent themselves well t o conductivity measurements. Ferric chloride proved to be insufficiently soluble. The saturated solution possessed a specific conductivity of about I 3.5 X IO-^ reciprocal ohms. Cadmium iodide is somewhat more soluble, but the specific conductivities of its solutions were less than I O X IO^ reciprocal ohms and did not appreciably change in passing from a concentration of fortieth- to seven hundred seventiethnormal. Silver nitrate, lithium chloride and ammonium chloride were sufficiently soluble in ethyl amine for the purpose in hand.
Electrical Conductivity of Solutions
539
TABLEI AgNO, in Ethyl Amine ~
Volume
1 Specific conductivity X
-
6.8 84 9.672 12.573
Molecular conductivity
104
-~
4.937 2.891 I. 842
i
9.062 7.965 6.418 4-858 3.399 2.796 2.31j 2.310 ~
0.51I
0.622 0.867 I .2 84 2.189 3.846 8.563
2 1.08
95.67
37.58 35.67 27.49 16.81 6.592 1.936 0.3382 0.6676 0 . 0 2 14
~~
1.920 2.217
2.384 2.158 1.437 0,745 0.289 0.134 0.191
NH,C1 in Ethyl Amine 0.9498 1.4233 2 303 3.709. 7.013 13.98 18.24 78.76
44.20 21-35 6.887 2.156 0.54 I 6 0.22 55 0. I 233 0.045 I
4.198 3.039 1.596 0.800 0.380 0.315 0.228
0.255
The molecular conductivities of solutions of silver nitrate in ethyl amine are roughly ten times as large as in similar solutions in amyl amine. I n the case'of both solvents the silver nitrate solutions are found t o conduct better than the other solutions examined. This behavior is in harmony with the presumption that stronger chemical affinities are brought into play in the solution of silver salts in amines than in the case of other salts. A correspondingly greater
540
Frederick L. Shinn
change in properties of both solvent and solute would therefore naturally be expected. The tables indicate that the molecular conductivities decrease in all cases up to a dilution of about eightieth-normal, and at greater dilutions they appear to undergo a slight increase. However, the values at high dilution are attended with some uncertainty, owing t o the limitations of the method when such high resistances are t o be measured, and the slight increase is within the limits of experimental error. The strdngest solutions of lithium chloride in ethyl amine show at first increasing molecular conductivities with increasing dilution, which attain a maximum at a dilution of about 0.8 normal. The ammonium chloride solutions may perhaps be more properly regarded as solutions of ethyl amine hydrochloride in ethyl amine, the ammonia having been replaced by the stronger base. The conductivities fall off as dilution progresses, finally attaining a minimum value. In passing from liquid ammonia to the homologous primary amines, using them as solvents, one observes a regular decrease in electrical conductivities of the solutions, and also a reversal of the parallelism between molecular conductivities and degree of dilution which obtains in the case of solutions in liquid ammonia. The molecular conductivities in ethyl amine decrease with increasing dilution and appear to tend toward a minimum, while in the case of amyl amine the values continue t o decrease as far as the dilutions could be carried. This last is true also for solutions in piperidine.’ Solutions in pyridine2 and its homologues, on the other hand, increase in molecular conductivity with increase of dilution. The substitution of oxygen for two hydrogen equivalents in ethyl amine produces a marked increase in the solvent power, particularly toward the alkali salts and increases also the electrical conductivities of the solutions. But here again the tendency of the amido group to gain the ascendency in Franklin and Kraus: LOC.cit. Lincoln: Jour. Phys. Chem., 3, 470 (1899).
Electrical Conductivity of Solutions
541
bringing about a decrease of the conductivity manifests itself, for the molecular conductivities of solutions of potassium chloride, potassium iodide and potassium cyanide in acetamide,' although such solutions are very good electrolytes (molecular conductivities 2 5 t o 40), reach maximum values and a t further dilutions diminish. From the standpoint of the theory of electrolytic dissociation the electrical behavior of solutions in primary and secondary amines and in amides, so far as such solutions have been studied, are inexplicable. The facts that for one and the same solute the molecular conductivities of solutions may not only be very large or very small, but may increase or decrease with dilution, or attain maximum or minimum values depending upon the specific nature of the solvent, suggest t h a t the r6le of the solvent in the process of the transmission of an electric current through a solution is, in all probability, a very active rather than an indifferent one, and does not materially differ from that of the solute. In such event the prevalent conception of " molecular conductivity " becomes not only meaningless but misleading. My acknowledgments are due Professor Kahlenberg for furnishing me with the ethyl amine which he has had on hand for some time with a view to making such measurements as are presented in this paper. Laboratory of Physical Chemistry, University of Wiscolzsin, M a y 18,1907.
Walker and Johnson: Jour. Chem. SOC., 87, 1597 (1905).
