PNNL

Abstract

Sodium carbonate is a common electrolyte in high pH aqueous solution, and its contribution to the viscosity of those electrolytes solutions is of practical importance. Nitrite is isostructural with carbonate, and has nearly identical ionic radius. The relative importance of ionic size versus interactions with water on electrolyte solution viscosity at moderate and high electrolyte concentrations has been ambiguous in the literature for a long time. Comparing the viscosity of sodium carbonate and sodium nitrate solution showed that carbonate solutions are considerably more viscous than nitrate solutions at constant sodium molality even though there is half as many anions in the carbonate solution as nitrate solution. This clearly shows that interactions with water are more important than ion size for the viscosity of these solutions because these two electrolytes with nearly identical ion size have very large differences in viscosity. This comparison was aided by new data on the viscosity of sodium carbonate solutions, which was also used to parametrize the Laliberté model of electrolyte solution viscosities between 20 and 98 °C.