The use of an inexpensive laser pointer to perform qualitative and semiquantitative laser refractometry

• Amarílis de Vicente Finageiv Neder ^[1] ; Edgardo García ^[1] ; Leonardo N. Viana ^[1]
  1. [1] Universidade de Brasília

     Universidade de Brasília

     Brasil

     
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 78, Nº 11, 2001, pág. 1481
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • 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.