Traffic Light Reaction

Purpose:

    A pale yellow solution in a flask is gently swirled and turns red. When the flask in shaken a green color develops.

Procedure:

  1. Dissolve 3 grams of dextrose and 5 grams of sodium hydroxide (NaOH) in 250 ml of water. Put 50 milliliters of this solution into a 250 milliliter flask.

  2. Add 5 to 10 milliliters of 1.0% indigo carmine indicator solution that is made up fresh. 1.0% solution is made by dissolving 1.0 gram of solid into 100 milliliters of 50% ethanol.

  3. Stopper the flask.

  4. At the beginning of the demonstration the color in the flask should be yellow. This is because the indicator is reduced by the alkaline dextrose.

  5. Gently swirl the flask to make the red color. Oxygen is now added to the reaction causing further reduction.

  6. Shake the flask and more oxygen reacts producing the green color.

Note:

  • If the red color does not persist, adjust the number of drops of indicator.

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