Description In the demonstration, a bottle of colourless liquid is shaken for a few seconds until the liquid turns blue. Upon standing for about a minute, the solution goes clear again. This sequence can be repeated many times. How does it happen? Essentially, it is an oxidation-reduction reaction. The bottle contains potassium hydroxide, glucose, water, and an indicator called "methylene blue". Glucose is a reducing agent and in alkaline solution it will reduce methylene blue …showed first 75 words of 186 total…

…showed last 75 words of 186 total…equations for the reaction are: when shaken: O2 + MB (colourless) -> MBox (blue) upon standing: RH + OH- -> R- + H2O MBox + R- -> MB + oxidation products of glucose where MB is the reduced (colourless) form of methylene blue, MBox is the oxidised (blue) form of methylene blue, and RH represents glucose. Methylene blue is an example of a "redox indicator". Some other redox indicators you may come across are ferroin, diphenylamine and indigo carmine.