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The Traffic Light Demonstration

Last updated

Feb 23, 2023
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- The States of Matter-- Starch Solution: Solid or Liquid?
- The Universal Gas Law Apparatus

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Chemical Concept Demonstrated

Reversible oxidation-reduction reactions

Demonstration

Indigo carmine is added to a 1:1 mixture of ethanol and water.
KOH is dissolved in water, dextrose (glucose) is added to this solution, along with the indicator solution.

Observations

When the indicator is initially added to the solution, the solution appears green. The color slowly fades to produces a yellow solution, passing through an intermediate stage in which the solution is red. The green color reappears when the flask is shaken and then fades to red, then yellow again.

Explanations (including important chemical equations)

Indigo carmine undergoes a reversible reduction.

Shaking the flask brings more oxygen into the solution, provoking the formation of the oxidized (green) form. The indigo carmine will eventually undergo reduction again to its reduced (yellow) form. The intermediate color is due to formation of a red semiquinone intermediate.

Contributors

Dr. George Bodner (Perdue University)

Chemical Concept Demonstrated

Demonstration

Observations

Explanations (including important chemical equations)

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