The refractive index of oxalic acid was measured by a refractometer using two different methods: zoom-in and extension methods. The zoom-in method requires two solvents which satisfy the following conditions: (i) a solid should have reasonable solubility in two solvents (10%), and (ii) the refractive index of the solid should be between those of two solvents. Two sets of solvents (i) DMSO and THF, and (ii) DMSO and n-PrOH were selected to determine the refractive index of oxalic acid, and the average value of 1.428(1) was obtained as its refractive index. The extension method, on the other hand, needs only one solvent to determine the refractive index of a solid; however, better solubility of a solid in the solvent was required compared to the zoom-in method. The refractive index of oxalic acid was measured indirectly from the linear relationship obtained between the % mass concentration of oxalic acid solution and its refractive index obtained by a refractometer. The refractive index of oxalic acid was determined in six different organic solvents, and the values were in the range of 1.409 and 1.427. It is noteworthy to mention that oxalic acid showed very good solubility in DMSO and MeOH (up to 52% by mass), and a good linear plot between the % mass concentration and its refractive index was observed for over 50% solution, which may support the assumption of the extension method that the straight line would be extended to 100% solution.

Refractive index of oxalic acid measured by zoom-in method and extension method

254th National Meeting (2017)

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