Blue Bottle Experiment
Materials: ★★☆ Available in most school laboratories or specialist stores
Difficulty: ★★☆ Can be done by science teachers
Safety: ★★☆ Some safety precautions required to perform safely
Categories: Colour Changes, Equilibrium, Oxidation and Reduction
Alternative titles: Shake-and-Change Redox Reaction
Summary
In the Blue Bottle Experiment, a solution of glucose, potassium hydroxide, and methylene blue alternates between colorless and blue when shaken.
Procedure
- Add 300 mL of distilled water to a 500 mL Erlenmeyer flask.
- Dissolve 8 g of potassium hydroxide in the water.
- Add 10 g of glucose (dextrose) and swirl until dissolved.
- Add 6–8 drops of methylene blue indicator.
- Allow the solution to rest until it becomes colorless.
- Stopper the flask and shake gently once or twice. The solution should turn blue.
- Let the solution sit until the blue fades back to colorless.
- Repeat shaking to restore the blue color several times until the glucose is consumed.
Links
Blue Bottle Equilibrium - North Carolina School of Science and Mathematics:
📄🎞️ Blue bottle - MEL Science: https://melscience.com/US-en/chemistry/experiments/blue-bottle-us/?srsltid=AfmBOoooZ5BHx5Tl9ufHBrt_Ulu0Dz2_7W-3fQqtMvthwNbHBwml2Wdl
📄 BLUE BOTTLE EXPERIMENT - QUT: https://cms.qut.edu.au/__data/assets/pdf_file/0014/24008/blue-bottle-experiment-teacher-worksheet.pdf
Variations
- Warm the solution slightly to observe the effect of temperature on reaction rate.
- Use different concentrations of glucose to see how long the color cycling lasts.
Safety Precautions
- Wear safety glasses to protect eyes.
- Potassium hydroxide is caustic and can cause severe burns—avoid skin and eye contact.
- Handle methylene blue with care, as it can stain skin and clothing.
- Dispose of chemicals according to institutional waste guidelines.
Questions to Consider
- What role does methylene blue play in this experiment? (It acts as a catalyst that cycles between oxidized and reduced forms.)
- Why does the solution turn blue when shaken? (Shaking dissolves oxygen, which oxidizes the reduced indicator back to its blue form.)
- Why does the color fade when the solution is left to stand? (Glucose reduces methylene blue to its colorless form in the absence of oxygen.)
- What eventually stops the color changes? (All the glucose becomes oxidized, or oxygen is depleted from the system.)
- How is this experiment an example of a reversible reaction? (The methylene blue cycles between oxidized and reduced states multiple times.)