A Classroom Demonstration of Red Nylon Dyeing with Japanese Madder ( Rubia Akane ) for Teaching Intermolecular Forces and Acid–Base Equilibria

This paper reports a rapid classroom demonstration and instructional activity based on nylon dyeing with Japanese madder ( Rubia Akane ), designed to support integrated learning of intermolecular forces and acid–base equilibria at the introductory undergraduate level. Using roots of home-cultivated madder, nylon fabric can be dyed a vivid red within approximately 10 minutes, providing an immediate and visually engaging starting point for discussion. The instructional focus then shifts to the molecular structure of the major dye component, purpurin (1,2,4-trihydroxyanthraquinone), enabling students to connect macroscopic color changes with otherwise invisible microscopic interactions. Compared with previously reported demonstrations of blue nylon dyeing using alizarin (1,2-dihydroxyanthraquinone), the present approach improves classroom safety by eliminating the need for strong bases. When implemented in a 50 minute session in a first-year engineering course, the activity led to improved student understanding of the mechanisms of intermolecular attraction and the concept of acid dissociation constants. From the perspective of sustainability and green chemistry, the use of naturally derived and locally grown materials represents a small-scale yet feasible approach to addressing the utilization of Earth’s limited material resources in individual classroom settings. This work aims to broaden access to chemical education by providing a classroom activity that can be implemented without specialized facilities, thereby offering learning opportunities to a wide range of students worldwide.