Blue Bottle Experiment Essay, Research Paper
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 to a colourless form. Shaking the bottle allows the oxygen in the air to oxidise the methylene blue to the blue form. Upon standing it is reduced by the glucose back to the colourless form. The 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.