Using Guided Inquiry to Study Optical Activity and Optical Rotatory Dispersion in a Cross-Disciplinary Chemistry Lab

We propose a new lab for the determination of the optical activity and optical rotatory dispersion of a compound. First our students determine the optical activity of S-(+)-carvone using the standard polarimeter (λ = 589 nm) . Then they are given a He-Ne laser with a detector and a polarizer and are asked to design the most accurate method of determining the angle of rotation for a second wavelength (λ = 633 nm). The method of guided inquiry is used throughout this part of the lab. The students ultimately should conclude that the most accurate data are obtained by using the orientation of polarizer where the intensity I of light exiting the polarizer is half of the sum of the minimal and maximal values, the reason being that this is the point where the slope of the I (θ) curve is maximal (θ is the angle between the plane of polarization of light and the axis of the polarizer). They then analyze the results and determine whether they are better described by the Drude equation or its modified version.