Blue Bottle Reaction

Reversible redox reaction that cycles indefinitely

Difficulty: Easy | Time: 15 minutes | Visual Impact: Very High

Historical Context

The blue bottle reaction was developed as a chemistry demonstration in the 1920s, though the underlying chemistry of methylene blue had been studied since the late 19th century. Paul Ehrlich, who won the 1908 Nobel Prize for his work on immunity, used methylene blue extensively in his research on selective staining and eventually on treating diseases.

The demonstration became famous through chemistry education programs and has been repeated millions of times in classrooms worldwide. Its appeal lies in the “magical” reversibility - the seemingly impossible return from colorless to blue by simply shaking the flask.

Materials

Procedure

  1. Dissolve 8g dextrose in 300mL water
  2. Add 10g sodium hydroxide and stir until dissolved
  3. Add 3-4 drops of methylene blue indicator
  4. Solution turns blue, then fades to colorless within a minute
  5. Shake the flask - solution turns blue again!
  6. Let stand - fades back to colorless
  7. Repeat the shaking/fading cycle many times

Reactions

\[\ce{MB_{ox} (blue) + glucose ->[OH^-] MB_{red} (colorless)}\] \[\ce{MB_{red} (colorless) + O2 -> MB_{ox} (blue)}\]

The Science

Glucose reduces the blue methylene blue to its colorless leuco form. Shaking introduces oxygen from air, which re-oxidizes the indicator back to blue. The cycle demonstrates reversible redox reactions and the role of oxygen as an oxidizing agent. The reaction can be repeated hundreds of times before the glucose is exhausted.

Resources