Transference numbers and hydration of some quaternary ammonium iodides

Cecil Harrison Hale, Purdue University


It is a generally accepted fact that ions in aqueous solution are hydrated to some extent. The degree of hydration ponds upon the size and charge of the ion and the temperature and concentration of the solution. A number of attempts have been made to determine the amount of solvent associated with various ions in both aqueous and non-aqueous solutions. These measurements have shown only the relative degrees of hydration, however, and not the actual amount of water associated with any one particular ion. Von Hevesy (8) has shown that nearly all univalent organic ions are so large and the strength of the electric field surrounding them so weak that hydration should not occur. This agrees with the results obtained by Lorenz (10) when he compared ionic mobilities with number of atoms in the ions. Walden (12) noted that the product of the equivalent conductance at infinite dilution and the viscosity of the solvent was more nearly a constant for solutions of tetraethylammonium iodide in various solvents than for other electrolytes. According to Stokes' law this product should be constant if the radius of the ion remains the same in different solvents. Since this is approximately true for the tetraethylammonium ion, it should be unsolvated. Studies of the electrical conductivities of tetramethyl- and tetraethylammonium salts made by Coates and Taylor (3) indicated that the quaternary ammonium ions are not solvated. If organic ions are not hydrated, the electrolytic transfer of water in solutions of tetraalkylammonium salts should show a transfer of meter to the anode equivalent to the amount of water carried by the anions alone. In this research, the electrolytic transfer of water in solutions of tetramethyl-, tetraethyl-, tetra-n-propyl-, and the tetra-n-butylammonium iodides was studied. Maltose was used as the non-electrolyte because it has a high optical rotation and its concentration can be measured very accurately by means of a polarimeter. Some experiments were also made in which acetone and ethyl acetate were the reference substances.



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