The conductivities of tetraethylammonium and ammonium salts in methyl alcohol

Abstract

If the motion of an electrolytic ion in an electric field obeys Stokes’s law and its effective radius remains unchanged in different solvents, then its velocity should be inversely proportional to the viscosity of the solvent, i. e ., l 0 X η = constant. The investigations of Walden have shown that this relationship, known as Walden’s rule, only holds good for certain large organic ions which therefore are presumed to be unsolvated. The NE t 4 + ion is of particular interest in this respect, since its salts have been studied by Walden in a number of solvents ; he has shown that the quantity A 0 X η is approximately constant for tetraethylammonium picrate both in different solvents and over a range of temperature in each. Owing to the lack of transport number data, the mobility of the NE t 4 + ion is only known directly in water, methyl alcohol and ethyl alcohol. Its value in these solvents is of considerable practical importance, since Ulich has used the average value of the product l 0 X η to calculate ionic mobilities in other solvents in which no transport numbers are at present available and in which they would be extremely difficult to measure in dilute solution. The value of the mobility of the tetraethylammonium ion in methyl alcohol is based solely on measurements with the picrate, apart from some early measurements with the iodide. The primary object of the present investigation was to measure the conductivity of a number of tetraethylammonium salts in methyl alcohol in order to obtain confirmatory evidence of its mobility. In addition, the conductivities of some ammonium salts have been determined in order to compare the mobilities of the simple and the tetra-substituted ammonium ion. It is remarkable that in spite of its complexity the NE t 4 + ion ( l 0 = 62) moves faster than the NH4 + ion ( l 0 = 58) and has a higher mobility in methyl alcohol than any cation except cæsium ( l 0 = 62·3 ) and hydrogen ( l 0 = 142), just as the symmetrical ClO 4 - ion is faster than the simple chlorine ion.