Verification of the Beer-Lambert Law Using Diluted Tomato Juice and a Halogen Lamp

I present a simple, inexpensive, and engaging laboratory activity designed for undergraduate chemistry education that illustrates the Beer-Lambert law using everyday materials. The choice of tomato juice as the colored analyte, due to its strong visible absorption from lycopene, a carotenoid pigment, makes this activity relevant to real-world applications. To prepare a concentration series, I diluted tomato juice with tap water to yield seven samples (0, 2.5, 5, 10, 25, 50, and 100%). Transmission spectra for each sample were recorded by passing light from a halogen lamp through a 1 cm cuvette and measuring the transmitted intensity with a spectrometer covering the visible region. The raw spectra revealed clear attenuation in the 480-520 nm region, consistent with the absorption band of lycopene. By converting the data to absorbance and plotting against concentration, I observed a linear relationship in the dilute region, confirming the Beer-Lambert law. At higher concentrations, deviations from linearity were evident, which can be attributed to scattering effects, molecular aggregation, and instrumental limitations. These deviations offer valuable opportunities for classroom discussions about the practical boundaries of the law, thereby preparing students for real-world applications. The activity requires only standard laboratory glassware and a broadband lamp, making it highly accessible. Its combination of visual impact, quantitative analysis, and discussion of limitations enhances student understanding of both the power and the boundaries of spectroscopic methods.