Chemical Traffic Light

The Chemical Traffic Light experiment demonstrates reversible redox reactions using glucose, sodium hydroxide, and indigo carmine. The solution transitions through a sequence of colors (blue → green → red → yellow) and can be reset by shaking, as oxygen from the air re-oxidizes the indicator.

1. Dissolve about 6 g of glucose in 200 mL of warm distilled water.
2. Add 40 mL of 1 M sodium hydroxide solution to make an alkaline mixture.
3. In a separate beaker, dissolve 0.01 g of indigo carmine in distilled water, forming a blue solution.
4. Combine the alkaline glucose solution with the indigo carmine solution in a larger beaker.
5. Observe the color change sequence: blue → green → red → yellow as the glucose reduces the indicator.
6. Shake or swirl the mixture to expose it to air. The solution will re-oxidize, shifting back toward green.
7. Repeat the shaking and resting process to demonstrate the reversibility of the color changes.

Chemical Traffic Light - Beautiful chemical Experiment! - Thoisoi2 - Chemical Experiments!:

Recreating the chemical traffic light reaction - NileRed:

📄 “Chemical Traffic Light” experiment - MEL Science: https://melscience.com/AU-en/articles/chemical-traffic-light-experiment/?srsltid=AfmBOor2O7ItMa_ExFTUu2axEoqOcZshStkxUHEa40TCuMR-bGgFDG6Y

• Try different sugars (fructose, sucrose) to see how they affect the timing of color changes.
• Warm the solution slightly to observe faster reaction rates.
• Use different concentrations of sodium hydroxide to see how pH influences the process.

• Sodium hydroxide is caustic—wear gloves, safety glasses, and a lab coat.
• Indigo carmine and other chemicals used may be toxic—avoid ingestion or skin contact.
• Conduct only under professional supervision, not as a casual home experiment.
• Dispose of chemical waste properly following institutional safety guidelines.

• Why does the solution change color over time? (Glucose reduces indigo carmine stepwise, creating different colored forms of the dye.)
• What role does shaking play in the experiment? (Shaking introduces oxygen, which re-oxidizes the dye and reverses the color change.)
• How does this experiment illustrate both oxidation and reduction? (Glucose is oxidized while the dye is reduced, and oxygen from air re-oxidizes the dye.)
• Why is indigo carmine a good choice for this demonstration? (It has multiple oxidation states with distinct visible colors.)