Many students enroll in college general chemistry with an interest in a medical career. In those (and alternative) careers, they will need to make critical decisions about data and how that data are acquired. A significant portion of introductory lab experiments are, in principle, but not necessarily in practice, devoted to understanding how chemical information is gained and how it is deemed reliable. Here we report on a laboratory experiment that is presented as a guided inquiry investigation grounded in the history of science and the link between early medicine and quantitative data. Oak gall extract is used to quantitatively determine the amount of iron present in a water sample using UV-vis absorbance. In this experiment, students are introduced to the Beer-Lambert law, calibration curves, and the reading of UV-vis spectra.