Bottoms Up to the Scientific Method

A laser refractometry experiment, which is appropriate for a general chemistry course, is described for use on the first day of class to introduce the scientific method. A common laser pointer is used to analyze the composition of ethanol/water solutions contained in a martini glass. A hypothesis, a tentative but clear and compelling explanation, is presented by the instructor regarding refraction of light. Students observe that alcohol content in water influences the position of a laser beam after being projected through a glass onto a white board. Students are asked to propose a law based on the observed differences in refraction of light by pure water and pure ethanol, and then the instructor tests this law using a cocktail. The inaccurate prediction of their law leads to a critical analysis of the problem and suggestions for additional experiments, which is followed up with a discussion on theory.