PNNL

Abstract

The refractive index (n) of a liquid is commonly measured in the chemistry laboratory using a refracrometer at a single wavelength (589 nm) and temperature (20 degrees C). The refractive index of a solid material is sometimes estimated by index matching to known liquids; when a solid "disappears" in a liquid medium, it is assumed to have the same index of refraction as the surrounding liquid. In both cases students may miss the fact that "n" is actually not just a single number, but rather a function of wavelength and temperature. In this laboratory, we employ UV-vis transmission spectra to obtain the dispersion curve (i.e., refractive index vs wavelength) of a solid material using a well-characterized organic solvent as a reference compound. While there are many experiments in the chemical education literature concerning the measurement and use of refractive index (3-6), we are unaware of any that employ the spectroscopic method used here. This exercise is most appropriate for use in the upper-division undergraduate physical chemistry lab, but could also be used in sophomore-level organic and analytical chemistry labs.