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Reversible Reaction

Chemicals and Solutions

  • KOH solution (8 g/ 300 ml water)
  • 10 g dextrose (glucose)
  • Methylene blue indicator


500 ml florence flask with rubber stopper


Put the potassium hydroxide solution in the florence flask and then add the 10 g of dextrose. Stir to dissolve the dextrose and then add six drops of methylene blue. When the indicator is initially added to the dextose/KOH solution, the solution appears blue. The color gradually fades to produce a colorless solution. To restore the color, give the flask one or two vigorous shakes. The color will reappear and then slowly fade.


The reaction: initially alkaline dextrose reduces methylene blue to form a colorless solution.

Upon shaking, oxygen from the air dissolves in the solution. This oxygen then reoxidizes the dye back to the blue form.