The importance of ion interactions on electrolyte solution viscosities determined by comparing concentrated sodium carbonate and nitrate solutions

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. Nitrate 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. The current study reviews and compiles the available literature data for carbonate and nitrate solution viscosities, and supplements these data with new measurements of the viscosity of sodium carbonate solutions. Given that carbonate and nitrate anions have nearly identical ion size, the large difference in observed viscosity indicate it that carbonate/nitrate ion interactions with water are more important than ion size in determining the viscosity of these two electrolyte solutions. Sodium carbonate viscosity data was also used to parametrize the Laliberté model of electrolyte solution viscosities between 20 and 98 °C. •Data on aqueous sodium carbonate solutions was fit to the Laliberte viscosity model•Aqueous Na2CO3 solution viscosity was considerably higher than nitrate solutions•Carbonate and nitrate have nearly identical ionic radius.•Stronger ion-pairing or interactions in carbonate solutions are responsible for the high viscosities.