This demonstration is sometimes knows as the blue bottle, the magic bottle or as the reversible methylene blue reaction.
Equipment typically required (per set):
- Small 500ml soft drinks bottle with lid or 500ml conical flask with bung
- 10g of Glucose (low hazard)
- 0.05g of Methylene blue (Harmful)
- 8g of Potassium hydroxide (Corrosive)
- 50ml of Ethanol (Harmful, Highly flammable)
- Conical flask (100ml)
- Stirring rod
Firstly, a solution of 0.05 g of methylene blue in 50 ml of ethanol needs to be made up in a separate flask. The 8g of potassium hydroxide is added to the empty bottle and 300ml of water added. The 10g of glucose is then mixed into this until completely dissolved. Finally 5 cm3 of the methylene blue solution is added.
The mixture in the bottle should become colourless within a minute or two. When shaken vigorously, the solution turns blue. This can be repeated several times.
The reaction occurs because shaking the bottle allows oxygen to dissolve into the solution, oxidising the methylene blue creating a blue colour. When the bottle is left, this oxygen is consumed. The methylene blue is reduced back to its colourless form by the glucose.
After several shakes, or if left unused for too long the solution may take on a yellow tinge and become unusable. Therefore this solution is probably best made fresh before every demonstration.