A two-period organic laboratory experiment that includes fluorescence sensing is presented. The pH-sensitive sensor MorphFl is prepared using a Mannich reaction between a fluorescein derivative and the iminium ion of morpholine. During the first laboratory, students prepare MorphFl. The second session begins with characterizing the sensor using standard techniques, followed by using MorphFl to analyze the relative acidity of several unknown aqueous solutions. MorphFl absorbs visible and near-UV light and emits a bright green fluorescence in aqueous solutions at low pH. At high pH, the emission of MorphFl is quenched. This laboratory experiment is appropriate for demonstrating condensation reactions, electrophiles, absorbance and emission of light by organic molecules, frontier molecular orbitals, and fluorescent sensors to any undergraduate audience. The visual component of the fluorescence assay provides an exciting alternative to more traditional organic laboratory experiments. (Contains 1 figure and 2 schemes.)