How to Do the Blue Bottle Chemistry Demonstration

In this reaction, glucose (an aldehyde) in an alkaline solution is slowly oxidized by dioxygen to form gluconic acid:

CH₂OH–CHOH–CHOH–CHOH–CHOH–CHO + 1/2 O₂ --> CH₂OH–CHOH–CHOH–CHOH–CHOH–COOH

Gluconic acid is converted to sodium gluconate in the presence of sodium hydroxide. Methylene blue speeds up this reaction by acting as an oxygen transfer agent. By oxidizing glucose, methylene blue is itself reduced (forming leucomethylene blue), and becomes colorless.

If there is a sufficient available oxygen (from air), leucomethylene blue is re-oxidized and the blue color of solution can be restored. Upon standing, glucose reduces the methylene blue dye and the color of the solution disappears. In dilute solutions the reaction takes place at 40-60°C, or at room temperature (described here) for more concentrated solutions.

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Index: How to Do the Blue Bottle Chemistry Demonstration

1. How to Do the Blue Bottle Chemistry Demonstration - Introduction and Materials
2. How to Do the Blue Bottle Chemistry Demonstration - Procedure
3. How to Do the Blue Bottle Chemistry Demonstration - Chemical Reactions
4. How to Do the Blue Bottle Chemistry Demonstration - Other Colors