chemistrytogether: Blue bottle, red bottle, and traffic light reaction

This week I want to show three reversible color changing reaction, and they are blue bottle, red bottle, and traffic light reaction. They are often used on magic shows or to perform demonstration experiments. However, though it seems to be complex and the ingredient should be the magician’s secret, I will reveal the secret to you today.

In fact, the mechanisms behind these amazing experiments are similar and easy to understand. When the bottle is shaken vigorously, one species in the solution would be oxidized (氧化) by the oxygen dissolving into the solution, and the color would change due to the different color that oxidized species has form the original one. After we put it aside and wait for a while, we could observe the color gradually return to the initial one. That is because the oxidized species has been reduced by the reductant (還原劑), usually glucose, in the solution.

Here are some videos:

blue bottle

red bottle and blue bottle (they are combined to make purple bottle)

traffic light

In the blue bottle reaction, the species being oxidized is methylene blue (亞甲藍); in the read bottle reaction, that would be resazurin (刃天青); in the traffic light reaction, that would be indigo carmine (靛胭脂). The indigo carmine has three oxidation states with different colors so the color depends on which level it has been oxidized.

methylene blue: