Construction and Evaluation of a LEGO Spectrophotometer for Student Use

Knagge, K.; Raftery, D. Construction and Evaluation of a LEGO Spectrophotometer for Student Use . Chem. Educator, 2002, 7(6), 371-375; DOI 10.1007 s00897020615a.

Dean Campbell and Ellen Freidinger

Department of Chemistry, Bradley University, Peoria, IL 61625, campbell@bradley.edu

The article “Construction and Evaluation of a LEGO Spectrophotometer for Student Use” by Kevin Knagge and Daniel Raftery is an excellent educational application of LEGO bricks. Readers of this article may also be interested in a somewhat simpler working LEGO photometer that uses the computerized LEGO RCX system. The RCX system powers a LEGO light bulb and measures light intensity using a LEGO light sensor (black tape is placed over the red LED emitter that is part of the sensor brick). All of the electronic LEGO parts that were used can be found in the Robotics Invention System 2.0. One of the very few non-LEGO parts used in this photometer is a sample solution holder that is made by gluing a plastic cuvette to a 2 peg x 2 peg brick to hold it in place on the base board. The LEGO photometer is simple to operate and is designed for a high school or junior high classroom. Since the light sensor is most sensitive to far red wavelengths, copper(II) sulfate solutions, which absorb the most light in the 790-830 nm range, can be used to demonstrate the instrument's capabilities. Since light intensity received by the RCX module decreases with increasing copper(II) sulfate concentrations, the absorbances of the solutions can be calculated. For example, the calibration curve plotting light absorbance as a function of molar concentration for copper(II) sulfate solutions is shown in Figure 1. The linear plot illustrates the relationship between solution concentration and light absorption. The building and operating instructions for this system are in the online book “Exploring the Nanoworld with LEGO Bricks,” produced by a collaboration between Bradley University and the University of Wisconsin-Madison. This book also contains directions for a wide variety of materials chemistry related LEGO models, and may be downloaded at no cost in PDF format from the web at http://mrsec.wisc.edu/edetc/LEGO/index.html.

Figure 1 – Absorbance as a function of molar concentration for copper(II) sulfate using the LEGO RCX photometer.

References

1. Knagge, K.; Raftery, D. Chem. Educator, 2002, 7, 371-375.