Conductance and viscosity studies of potassium iodide and tetrabutylammonium iodide in formamide

Abstract

Conductance studies of tetrabutylammonium iodide and potassium iodide solutions in formamide were made at temperatures of 10°C, 27°C, 40°C and 50°C over a series of concentrations ranging from 0.0005 to 0.15N. Formamide is an associated solvent with a high dielectric constant and extensive studies have not been made so far because of the difficulties involved in its purification and preservation. Tetrabutylammonium iodide and potassium iodide provided an interesting study with a common anion but with cations of different sizes and charge densities. Conductance studies revealed that tetrabutylammonium iodide acted as a strong electrolyte whereas potassium iodide behaved as a weak electrolyte. Limiting equivalent conductances of tetrabutylammonium iodide were evaluated using Shedlovsk's equation which compared well with values obtained from using the Fuoss-Onsager equation.

A suitable explanation could not be given for the unusual behavior of potassium iodide in formamide. Though the smaller size and the higher charge density on the potassium ion when compared with that of tetrabutylammonium ion are indications of strong solvation, it is possible that in the case of potassium ion solvation is ion-solvent interaction without the attachment of specific solvent molecules. Hence the less solvated potassium ion permits the close approach of iodide ions resulting in the formation of ion-pairs.

Viscosity studies were conducted for both potassium iodide and tetrabutylammonium iodide at 10°C, 27°C and 40°C over a series of concentration ranges. Studies revealed deviations from linearity from the Jones and Dole equation. These deviations were explained as due to the depolymerization of association solvent molecules causing a net decrease of viscosity. this decrease in viscosity in theses systems was more than the increase in viscosity due to the friction of ions on the solvent molecules, thus causing negative curvatures at low concentrations.