Animated video: 37 principles of chemical reactions and their dangers---Traffic lights

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Principle: The solution in the bottle contains 3 components: sodium hydroxide, D-glucose, and indigo carmine (also known as acid indigo). Indigo carmine is a redox indicator; at the same time, it also functions as an acid-base indicator. In other words, under the influence of redox reactions and pH levels, it can change color in various ways. Indigo carmine has three different redox states. In this reaction system, when the bottle is shaken, it is oxidized by oxygen in the air, and when left at rest, it is reduced by glucose, which results in a color change. If the reaction takes place in different pH environments, the color will also change accordingly. The specific color change states are summarized in the figure below: redrawn based on information provided by the Royal Society of Chemistry. Trivia: Besides being used as an indicator, indigo carmine has other uses as well. It is a food coloring (E132), and it is also used in some urinary system surgeries. Risk: Low. Here, sodium hydroxide serves to adjust the pH; very concentrated solutions are not used, and glucose as well as indigo carmine are also relatively safe. Recorder: Royal Chemistry Society