Solution change colors as a traffic light
name: Indigo carmine in alkaline glucose solution undergoes a reversible redox reaction with oxygen from air
The oxidized form of indigo carmine is green in an alkaline solution. The indicator reduces in a glucose alkaline solution. The intermediate form of indigo carmine is red. The fully reduced form of the indicator is yellow.
When the flask is shaken, oxygen from air dissolves in the solution and oxidizes indigo carmine. Solution becomes red if a small amount of oxygen is dissolved (moderate shaking), and green if all of indigo carmine was oxidized (intensive shaking).