- Tap water
- 2 one litter conical flask with stopper.
- 7.5 g glucose ( 2.5 g for one flask : 5 g for other flask )
- 7.5 g NaOH
- 0.1 % solution of methylene blue ( 1 ml for each flask )
- Half fill two one liter conical flasks with tap water.
- Dissolve 2.5 g of glucose in one of the flask ( A ) and 5 g of glucose in the other flask ( B )
- Dissolve 2.5 g of NaOH in flask A and 5 g of NaOH in flask B.
- Add 1 ml of 0.1 % of methylene blue to each flask.
- Set a flask a side. The liquid will gradually becomes colorless.
- The blue color of the solution can be restored by shaking the contents of the flask.
Gluconic acid is converted to sodium gluconate in the presence of NaOH. Methylene blue speeds up this reaction by acting as an oxygen transfer agent. By oxidizing glucose, methylene blue is itself reduced ( leucomethylene blue ) and becomes colorless. Leucomethylene blue is re-oxidized and the blue color of solution can be restored.