The extension method which was developed based on the observation of a good linear relationship between the percent mass of solution (solid solute and liquid solvent mixture) and its refractive index has been used to determine the refractive index of solid compounds such as fatty acids, organic compounds, and ionic compounds. In the system, a plot of refractive index vs. percent mass was obtained in low concentration ranges (typically 0-24%), and the line of the linear plot was then extrapolated to 100% mass (i.e., pure solid) where the refractive index of the solid was calculated. The extension method has been further applied to measure the refractive index of calcium nitrate because it showed good solubility in various organic solvents such as methanol, DMSO, acetone, and THF. In the experiment, a linear relationship was observed between the refractive index and % mass of calcium nitrate in a solvent, and a first order linear equation was calculated based on the plot. By applying 100 to the % mass variable (100% mass means pure solute, the solid compound) in the linear equation, the refractive index of calcium nitrate was indirectly determined for the solvent. Based on the data measured in methanol solution of calcium nitrate, a linear equation (e.g., y = 0.001210x + 1.327941) was obtained, then a value of 100% was applied to get the refractive index of calcium nitrate, which was 1.449. After two more trials, 1.449(1) was determined as the refractive index of calcium nitrate in methanol.

Determination of the refractive index of calcium nitrate measured by the extension method

256th National Meeting (2018)

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