Oscillating Clock Reaction

The Briggs-Rauscher reaction is a dramatic oscillating chemical reaction in which a solution alternates between amber and blue-black colors several times before settling into a final dark-blue state. The color changes are caused by the interplay of iodine species, hydrogen peroxide, malonic acid, starch, and a manganese catalyst.

1. Prepare three separate solutions (A, B, and C) as instructed, each containing the required chemicals dissolved in distilled water.
2. Heat and dissolve starch in water to make a colloidal solution, then add it to solution C.
3. To perform the demonstration, combine equal volumes of solutions A and B in a beaker.
4. Immediately add the same volume of solution C to the mixture.
5. Observe as the solution oscillates between amber and blue-black colors every few seconds.
6. After several minutes, the oscillations will stop, leaving the solution dark-blue.

The Briggs-Rauscher Iodine Oscillator - mrhomescientist:

Recreating the Briggs-Rauscher oscillating reaction - NileRed:

📄 Briggs-Rauscher Reaction - ChemTalk: https://chemistrytalk.org/briggs-rauscher-reaction/

• Scale the volumes up or down depending on the size of the audience.
• Experiment with slightly different starch concentrations to vary the intensity of the blue color.
• Record the oscillations with a camera and play back in time-lapse to emphasize the repeating changes.

• Wear safety glasses, gloves, and a lab coat when handling all chemicals.
• Handle 30% hydrogen peroxide with care; it can burn skin.
• Handle sulfuric acid with caution; it is highly corrosive.
• Avoid inhaling iodine vapors; they are toxic and corrosive. Perform the reaction in a well-ventilated area or fume hood.
• Clean spills and stains with a sodium thiosulfate solution.
• Dispose of the final solution properly using sodium thiosulfate neutralization.

• Why does the reaction oscillate between colors rather than simply changing once? (Because some reactions proceed quickly while others are slower, causing periodic changes in the concentration of iodine species.)
• What role does the starch play in the demonstration? (It forms a visible blue complex with triiodide ions, making the oscillations easier to observe.)
• How does the manganese (II) ion affect the reaction? (It acts as a catalyst, producing intermediate species that help drive the oscillations.)
• What eventually causes the oscillations to stop? (One or more reactants are consumed, preventing further regeneration of intermediates.)