The Blue Bottle Demonstration
A bottle containing a colorless solution is shaken and instantly turns blue. The blue bottle is left to sit for a few minutes and returns to a colorless state. If shaken again, the bottle will again become blue.
In the presence of OH-, glucose is converted to gluconic acid. This reaction provides H+ and 2e-, which act to convert methylene blue from it’s oxidized (blue) form to it’s reduced (colorless) form. When the bottle is shaken, O2 from the upper portion of the bottle is associated into the solution. This causes an oxidation of the reduced form of methylene blue, re-creating the blue color. If left to sit, the O2 will come out of solution and the reduced form of methylene blue will be re-created.