Using Project-Based Learning To Design, Build, and Test Student-Made Photometer by Measuring the Unknown Concentration of Colored Substances

Students learned the principles and practice of photometry through project-based learning. They addressed the challenge of measuring the unknown concentration of a colored substance using a photometer they were required to design, build, and test. Then, they used that instrument to carry out the experiment and fulfill the challenge. A photometer was designed and built by students consisting of a green laser pointer as the light source and a lux meter as the detector and readout. Using this photometer students have determined the concentration of the unknown sample of KMnO4 solutions. The concentration of this sample solution was calculated to be (4.62 +/- 0.06) x 10(-4) M; this value agrees within 6% of the expected value from the measurement using the commercial spectrophotometer which was calculated to be (4.96 +/- 0.005) x 10(-4) M. The experiments fit well into an analytical chemistry course and take a standard (1 h) lab period. This project has facilitated improved student understanding of the photometry concepts and increased the creative problem-solving. In general, the students' response to this laboratory was positive.