JChemEd Article Describes an Experiment using Smart Phones as Spectrophotometers

AACT members now have access to 25 ACS Publications articles each year. We are highlighting one article each month that you might consider downloading through this new member benefit. This month, we are featuring a hands-on student activity from the July 2016 issue of the Journal of Chemical Education titled Teaching Beer’s Law and Absorption Spectrophotometry with a Smart Phone: A Substantially Simplified Protocol by Thomas S. Kuntzleman and Erik C. Jacobson.

The AP Chemistry Course and Exam description contains several references to the use of spectroscopy and Beer’s Law. Appendix A: Preparing Students for Success in AP Chemistry states that students should be able to analyze and interpret data from spectroscopy experiments using Beer’s Law. Traditionally, this would require the purchase of a spectrophotometer and related equipment, an expensive purchase for schools with limited budgets. This JCE article outlines a simple and effective way for students to use their smart phones and other everyday items to gather Beer’s Law data. The teacher background information and student activity sheet are available as downloads in the supporting information link.

Prior to the activity, students download an RGB analyzer, such as Colorimeter from iTunes, to their smart phones. The applications should be able to give the average RGB value of the light that passes through a CuSO₄ solution. They then use a cardboard box to house samples of CuSO₄ ranging in concentration from 0.10M to 0.50M. Red paper is placed in the box behind the area where the samples will be placed. Red paper is used because red light is best absorbed by the blue CuSO₄ solution. The sample box is secured to a heavy book or the lab bench to ensure that it does not move during the experiment.

Cuvettes are not required for this experiment, but they can be used if you have them available. If not, you can use clean test tubes or clear plastic cups. A hole is cut in the top of the box to securely anchor the solution sample in place. A larger square hole is cut in the front and in the back of the box. One allows light to pass through the CuSO₄ sample in the cuvette and the other is used to enable the smart phone camera to detect the light that passes through the sample.

Students test a blank sample first and then nine samples of CuSO₄ with increasing concentration. They use the colorimeter app to determine and record the R value for each. They then calculate the absorbance using the following equation: A = -log (I/I₀). Note that the R value recorded for the blank sample is I_o. The absorbance and concentration data are plotted and analyzed in Excel. Students can then determine the concentration of an unknown solution using their graph.

This activity offers an easy method to give students the opportunity to learn about spectroscopy with inexpensive and readily available equipment. The lab is easy to set up and produces excellent results. It is an effective alternative for teachers who do not have the funds to purchase a spectrophotometer.

AACT has several Beer’s Law resources in our high school library. They can be downloaded in the sidebar of this page. If you have a favorite ACS Publication article that you use in your classroom, please share it with us at AACTconnect@acs.org.