recently, I finally bought a reagent and did the legendary traffic light experiment ~ to share with you the video I shot:

as long as the solution of this experiment is shaken and set, it will change back and forth between yellow, red and green. This is why it is called "traffic light". However, unlike the traffic lights, the "red light" is the middle state in the experiment. the solution stays yellow for a long time when it is still, turns red if it shakes a little, turns green when it shakes violently, and turns red at a relatively fast speed when it stops shaking, and then slowly turns yellow.

this is a redox reaction that occurs in an alkaline environment. There are three key substances in the solution: ① sodium hydroxide, which provides an alkaline environment; ② glucose, which acts as a reducing agent; and ③ indigo carmine, a pigment that acts as both an acid-base indicator and a redox indicator, meaning that it shows different colors in different oxidation states.

and there is actually another reactant added to this reaction: oxygen in the air. Indigo carmine is blue when it dissolves in water and appears green when it is first dripped into the reaction solution: this is its color in an alkaline environment. Next, indigo carmine is reduced by glucose in the solution, which is carried out in two steps, the first step is to produce a red product, and the second step is yellow. When shaking the bottle, the yellow product reacts with oxygen in the air, oxidizes in two steps, and then turns red and green. This color change can be repeated many times (exactly how many times I haven't tested it, but you should be able to do it by the time you get tired of it. ).

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(the color of indigo carmine in different pH and redox states, the traffic light reaction is the middle line)

the test itself is not difficult to operate, of course, it should be carried out in the laboratory. For me, this experiment is mainly stuck in finding a stopper that matches the bottle. There is no suitable rubber stopper in the lab, so we can only use glass stopper first. Because this experiment has to shake hard to turn green, be sure to cover the cork and wear gloves to avoid spilling the reaction solution on your hands.

for more information on how to do this, please see here: http://www.rsc.org/learn-chemistry/resource/res00001007/traffic-lights-demonstration