Cola beverages are widely consumed and popular among students; they can be used as safe reagents to replace toxic chemical dyes. In this study, a safe and improved experiment is described, which successfully demonstrates Beer's law and adsorption process using activated carbon as the adsorbent and cola as the adsorbate. The results of this study demonstrate that the use of cola has achieved good evaluation for the teaching of the Beer's law and the adsorption phenomenon. The potential learning outcomes of the experiment include the principles of spectrophotometry, operation of spectrophotometer, Beer's law and its limitations, derivation of linear regression equation, and construction of adsorption isotherms. This experiment can be used as a safe spectrophotometric protocol to determine the adsorption isotherms for undergraduate learning of analytical or general chemistry.