Simultaneous Determination of Refractive Index and Density of an Evaporating Aqueous Solution Droplet

The experimental technique and computational method developed for simultaneous determination of refractive index and density of an electrolyte solution droplet undergoing evaporation at 25°C are described. Results are presented for the systems (NH4)2SO4-H2O, Na2SO4-H2O, and NaNO3-H2O over a wide concentration range from high dilution to critical supersaturation. It is shown that the partial molal refraction derived for each electrolyte is remarkably constant throughout the entire concentration region, thereby validating the partial molal refraction approach for predicting the refractive index of highly supersaturated solutions.