Analytical chemistry, particularly instrumental analysis, often involves the use of modular, computer-controlled instrumentation, reducing the opportunity for students to appreciate the role of physics and engineering in analytical chemistry.  Here, in a multi-week laboratory exercise, students build and test a very simple spectrophotometer (colorimeter).   Students use their instrument to conduct a comprehensive study of the Beer-Lambert law and also are afforded a deeper understanding of molecular spectroscopy.  In addition to testing the relationship between pathlength and concentration to absorbance, an estimate of molar absorptivity for a transition-metal compound is also obtained.  Deviations from Beer's Law were also investigated.  Ultimately, through testing of the same solutions using a HP8453 diode array spectrophotometer, the wavelength of the light source used in the instrument is also estimated. A portable fiber optic cable is also used to verify the wavelength of the light emitting diode (LED) used as light source. All student teams obtained correlation coefficients = 0.9 for the relationship between concentration and absorbance and pathlength and absorbance. Student feedback (at the time of the experiment and through end of semester course evaluation) indicates  that the vast majority of students believed  this experiment provided a valuable learning experience; this was evidenced in student performance on related questions in the final course examination.

Investigation of Beer's law using a student-built instrument

243rd National Meeting (2012)

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