Science Trick: Traffic Light Reaction

Why does the solution turn red, yellow and green? Here is a quick demonstration!


What is in the solution?

  • Sodium hydroxide – makes the solution basic
  • Glucose – acts as a reducing agent (loses electron)
  • Indigo carmine – indicator for the reaction


What is happening?

  • Indigo carmine can exist in oxidised (loss of electron ), reduced (gain of electron) and intermediate forms.
  • Each form has a slightly different structure which means that each structure absorbs a different frequency of light; hence the three different colours – red, yellow and green.