Resumen de The use of an inexpensive laser pointer to perform qualitative and semiquantitative laser refractometry
Amarílis de V. Finageiv Neder, Edgardo García, Leonardo N. Viana
In this paper we describe a simple low-cost laser refractometry experiment designed to be executed by inexperienced students or as a classroom demonstration. The purpose of this experiment is to estimate the refractive index (n) of different liquids using a 25-mL beaker and a pocket laser pointer. A pair of chemically related substances for which the refractive indices are found in handbooks is selected, and the relative locations where the laser beams hit a paper screen after being refracted by the two chosen substances and two reference substances are compared. It is recommended that substances with very different n values be used as references, such as water (1.332) and toluene (1.496). In this way any other substance with n within this range can be identified according to the proximity of the refracted beam to one extreme or another. This procedure enables one to distinguish between ethanol (1.361) and 1-propanol (1.385), acetone (1.359) and butanone (1.379), cyclohexane (1.427) and hexane (1.375), ethyl ether (1.353) and tetrahydrofuran (1.405), among other possibilities. An excellent linear correlation between n and the laser beam position on the screen is found, allowing a semiquantitative nestimation for an unknown sample.
