Blue Bottle Demonstration (continued)
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Follow-up:
• For best reaction, make your solutions just prior to use.
• To manipulate the speed of the color change, you can vary the temperature of the solution, as well as concentration of the
Methylene Blue indicator.
– Speed Up Color Change
a. Increase temperature of the solution.
b. Increase concentration of the Glucose and Sodium Hydroxide.
c. Decrease concentration of the Methylene Blue Indicator.
Teaching Notes:
• Methylene blue indicator is colorless when in the presence of a reducing agent but is blue in the presence of an oxidizer.
• The upper layer of the solution remains in contact with the air inside the beaker and will remain slightly blue.
• Photochemical Variation:
– Add 2.0 g of Iron(II) Sulfate to 100mL of 0.1M Sulfuric Acid solution in a 250mL Erlenmeyer flask
– Add a couple crystals of methylene blue. Mix.
– The solution should turn nearly colorless when placed on an overhead projector, or under an
otherwise strong light source.
a. If it remains blue, dilute the solution with water.
Disposal/Clean-up:
• Neutralize the solution by adding dilute hydrochloric acid (0.5M, until the pH is approximately 7)
• Chemical disposal should be done in accordance with all local safety and environmental regulations.
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MB(oxidized) + C6H1206 + NaOH —> MB(reduced)
Blue Colorless
MB(reduced) + C6H1206 + NaOH + O2 (via shaking) —> MB(oxidized)
Colorless Blue
