Abstract: Cochineal, a natural animal pigment extracted from female cochineal insects (Dactylopius coccus) that parasitize cacti, is widely utilized in food, pharmaceutical, and cosmetic industries due to its safety and non-toxic properties. This popular science experiment investigates the chromatic transition (orange-red-purple) of cochineal in solutions with varying pH levels, along with its colorimetric reactions with metal ions (copper, iron, calcium) to form distinct complexes. The chemical principles underlying these phenomena were examined through UV-Vis absorption spectroscopy. By leveraging cochineal’s color-changing properties, we developed two types of colorimetric cards for public science education, demonstrating applications in pH determination, metal ion identification, and concentration measurement in common consumer products including foods, daily necessities, and health supplements. The experiment features environmentally friendly reagents, straightforward procedures, visually striking results, and high safety standards, making it particularly suitable for multi-level chemical education targeting K-12 students and the general public. This work highlights the unique scientific and societal value of natural animal-derived pigments through engaging hands-on demonstrations.

Key words: Cochineal, Acid-base color change, Metal ion detection, Colorimetric card