Beer's Law

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Spectroscopy, the study of the interaction of matter with electromagnetic radiation, can be used for qualitative and quantitative analysis. This Demonstration shows the importance of choosing the appropriate wavelength at which to analyze a hypothetical sample solution containing an analyte in a noninteracting solvent. Additionally, the effects of solution concentration can be explored using Beer’s law: , where  is absorbance, ϵ is the molar absorbtivity (in L  ), is the path length of the sample (in cm) and is the concentration of the compound in solution (in mol ).


The first slider changes the wavelength of the radiation. The absorptivity coefficient changes as a result, which consequently alters the absorbance under the specified conditions. The lower plot shows simulated data, with random associated error. You can use the slider to investigate how to choose the best wavelength to achieve the most accurate and precise experimental measurement of the absorptivity coefficient.

The second slider adjusts the concentration of the sample, to observe the effect of analyte concentration on absorbance for any given wavelength.

This Demonstration uses data for a hypothetical situation; the wavelength of peak absorbance and error values may differ for actual analytes and experimental trials.


Contributed by: Scott Berger, Rachael Holappa and Kaitlin Nguyen (May 2019)
Project was overseen by Prof. Heidi Hendrickson at Lafayette College, Easton PA.
Open content licensed under CC BY-NC-SA



The spectrum provided is generated using [1].


[1] "Creating UV/Visible Plots from the Results of Excited States Calculations." (May 22, 2019)

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