Unlike the large number of laboratory experiments on phase-transfer catalysis (PTC) that focus on a catalyzed chemical process, the present laboratory emphasizes the mechanism of phase transfer catalysis itself. Students can follow visually the actual transfer of the reagent by the catalyst, and its consumption in the organic phase, in a step-by-step process that employs a colored charge-transfer (CT) complex as the transferred reacting species. Consumption of the transferred nucleophile is followed by discoloration of the organic phase. This transfer consumption cycle can be repeated several times by shaking the two separated phases again,allowing students to finally grasp the whole process as a continuous repetition of these cycles.The experiment also links, through visualization, the important synthetic tool of PTC with abstract concepts based on molecular-orbital and hard-soft acid-base theories, invoked in the formation of a CT complex.