Abstract
Students have long enjoyed color-change demonstrations and experiments. This paper describes the development of purple color in aqueous solutions of anthocyanins by the addition of alum, which enhances the color intensity, and neochlorogenic acid, which enhances the color stability. The range of colors can be further extended with high visual impact by changing the pH of the solutions. Variations of this demonstration are presented that can be adapted for a wide range of educational settings, including using typical anthocyanins to illustrate the chemistry of complexation for undergraduate students (part I); using morning glory flowers to observe a natural dye rainbow suitable for elementary school students; and using different combinations of pH and metal ions to demonstrate coordination complexes for high school students (part II). Follow-up lessons on chemical color stability are possible, given the enduring color of these solutions, even after several months. Suggestions for alternative materials that can be used to conduct these demonstrations are provided to ensure availability for teachers around the world.
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