The blue bottle reaction is a classic color change chemistry demonstration. It interests students in chemistry, introduces the scientific method, and illustrates oxidation and reduction (redox reactions) and chemical kinetics. The reaction starts as a blue liquid which becomes colorless and returns to its blue color.
The usual materials for the Blue Bottle chem demo are:
- 8 grams potassium hydroxide (KOH)
- 10 grams dextrose
- Methylene blue solution (0.25 g methylene blue in 1000 mL water)
- 500-mL flask with stopper
You can make substitutions for the chemicals. In place of potassium hydroxide, you can use another strong base, such as sodium hydroxide (NaOH). Glucose may be used in place of dextrose. Several redox indicator dyes can be used instead of methylene blue. These include indigo carmine (green-red-green), resazurin (Vanishing Valentine), thionine (purple), or FDC Blue #1 (Gatorade and drain cleaner Blue Bottle demo).
The base solution (NaOH or KOH) can be prepared in advance, but it’s best to add the sugar and methylene blue just prior to the demonstration.
- In the flask, dissolve 8 grams potassium hydroxide in about 300 mL of water.
- After the solution has cooled, add 10 grams of dextrose.
- Add about 1 mL of methylene blue solution to the flask and stopper it. The ideal volume produces a solution that turns colorless upon standing, but becomes blue when the flask is shaken. If necessary, add more dye dropwise to achieve the desired effect.
- For the demonstration, shake the flask so that the solution is blue. Allow it to rest to turn colorless.
Exploring Chemical Kinetics
The Blue Bottle demonstration may be used to explore chemical kinetics. One variation on the demo is two use two 500-mL flasks, one with 2.5 g NaOH or KOH, 2.5 g glucose or dextrose, and 1 mL methylene blue and the other with 5.0 g NaOH or KOH, 5.0 g glucose or dextrose, and 1 mL methylene blue. Stopper and shake the flasks to start the reaction and compare the effect of concentration on the rate of the chemical reaction. Temperature also affects rate of reaction. KOH or NaOH solutions may be placed in hot and cold water baths before adding the sugar and methylene blue.
How It Works
Students can appreciate the blue bottle reaction and make predictions about its behavior if temperature or reactant concentrations change without understanding the chemistry. However, the reaction is well-studied. Dissolved oxygen oxidizes glucose to form gluconic acid. The sodium hydroxide converts gluconic acid into sodium gluconate. Methylene blue acts as an indicator, but also speeds the reaction by serving as an oxygen transfer agent. As it oxidizes glucose, methylene blue is reduced to form colorless leucomethylene blue. Shaking the stoppered bottle introduces fresh oxygen into the solution and reoxidizes methylene blue, returning it to its blue form. While the color change is reversible and the demonstration may be performed many times, eventually the solution turns yellow or brown.
Safety and Disposal
Avoid contact with the strong base and its solutions. Sodium and potassium hydroxide are caustic chemicals, capable of producing a chemical burn. As always, it’s best to wear safety goggles, gloves, and a lab coat (or similar forms of protective gear). The reaction neutralizes the base, so it’s safe to pour the solution down the drain. If you want, you can neutralize any excess base using a weak acid (e.g., vinegar) before disposal.
- Dutton, F. B. (1960). “Methylene Blue – Reduction and Oxidation”. Journal of Chemical Education. 37 (12): A799. doi:10.1021/ed037pA799.1
- Engerer, Steven C.; Cook, A. Gilbert (1999). “The Blue Bottle Reaction as a General Chemistry Experiment on Reaction Mechanisms”. Journal of Chemical Education. 76 (11): 1519–1520. doi:10.1021/ed076p1519
- Limpanuparb, Taweetham; Areekul, Cherprang; Montriwat, Punchalee; Rajchakit, Urawadee (2017). “Blue Bottle Experiment: Learning Chemistry without Knowing the Chemicals”. Journal of Chemical Education. 94 (6): 730. doi:10.1021/acs.jchemed.6b00844