An experiment is described where students troubleshoot a published procedure for the analysis of ethanol. UV-vis spectroscopy is used to measure the change in absorbance upon reaction of dichromate with ethanol. The experiment requires the students to critically evaluate their experimental results to correct a fundamental flaw in the original written procedure. Students can use the results and the corrected procedure to understand the limits of sensitivity of the instrumentation used for the absorbance measurements. (Contains 2 tables and 1 figure.)