From Plant to Practice: Exploring Justicia spicigera as a Natural pH Indicator in Chemistry Education

Chemistry education seeks materials for inspiring students for deep analysis to reinforce fundamental concepts. This study explores the potential of Justicia spicigera (commonly known as muicle), a plant traditionally used in Mexican herbal medicine and known for its intense pigmentation, as a low-cost, natural acid–base indicator. A chlorophyll-diminished aqueous extract of J. spicigera (CDE) was prepared and characterized spectrophotometrically within a pH range of 2–10. The extract exhibited a distinct color change from orange to purple in the pH range of 3.5–5.5, consistent with the behavior of anthocyanin-based indicators. The apparent dissociation constant (pKIn, app) was 5.6 ± 0.2. Eighteen undergraduate students successfully used this natural extract as an indicator in an acid–base titration of sodium bicarbonate with hydrochloric acid. The students used JAMOVI software to statistically analyze the experimental data to analyze the performance of the indicator. The natural and synthetic indicators exhibited comparable precision and accuracy within the studied experimental context. Furthermore, the natural indicator provided distinct and consistent color transition at the titration end point, confirming its suitability for analytical applications. The proposed activity promoted green chemistry principles and student engagement and highlighted the cultural and scientific value of traditional plants while developing essential data analysis skills.