Réaction Oscillante de Briggs-Rauscher

Une horloge chimique qui alterne entre incolore, ambré et bleu profond

Classroom Demonstrations Advanced (University) 40 min ~$20,00

Objectif

Observer une réaction chimique oscillante qui cycle répétitivement entre trois états de couleur distincts, démontrant la cinétique chimique non linéaire.

Contexte

The Briggs-Rauscher reaction is one of the most visually stunning demonstrations of oscillating chemical kinetics. Three solutions are mixed, and the resulting solution spontaneously cycles between colorless, amber, and deep blue states for several minutes. The oscillations occur because two competing reaction pathways alternately dominate: a radical pathway (producing I₂, which reacts with starch to form the blue color) and a non-radical pathway (consuming I₂, clearing the blue).

Avertissements de sécurité

  • 30% H₂O₂ causes burns — handle with extreme care
  • H₂SO₄ is corrosive
  • KIO₃ is an oxidizer
  • Wear face shield during mixing step
  • Do not lean over the reaction vessel

EPI requis

goggles gloves lab_coat

Matériaux

  • Potassium iodate (KIO₃) (4.3 g)
    Solution A component
  • Malonic acid (CH₂(COOH)₂) (1.6 g)
    Solution B component
  • Manganese(II) sulfate (MnSO₄) (0.4 g)
    Solution B catalyst
  • Starch solution (1%) (5 mL)
    Solution B indicator
  • Hydrogen peroxide (30%) (50 mL)
    Solution C
  • Sulfuric acid (1M H₂SO₄) (20 mL)
    Solution A acidification
  • Distilled water (500 mL)

Équipement

Beakers (500 mL, 3 for solutions + 1 for mixing) Magnetic stirrer and stir bar Graduated cylinders White background paper

Procédure

1

Prepare Solution A: Dissolve 4.3 g KIO₃ in 100 mL warm water. Add 20 mL of 1M H₂SO₄.

5 min Handle acid carefully
2

Prepare Solution B: Dissolve 1.6 g malonic acid and 0.4 g MnSO₄ in 100 mL water. Add 5 mL of 1% starch solution.

5 min
3

Prepare Solution C: Dilute 50 mL of 30% H₂O₂ to 100 mL with water.

3 min 30% H₂O₂ is corrosive
4

Set the magnetic stirrer to moderate speed. Pour all three solutions simultaneously into the large beaker on the stirrer.

2 min Step back after mixing
5

Observe: the solution cycles colorless → amber → deep blue → colorless, repeating for 5–15 minutes. Time the oscillation period.

15 min
6

Record the number of oscillations and the period of each cycle. Note how the period changes over time.

5 min
7

Discuss the mechanism: competing radical and non-radical pathways, the role of iodine and starch, and the concept of chemical oscillators.

5 min

Résultats attendus

The solution oscillates between colorless, amber, and deep blue 10–15 times before settling to a permanent dark blue. Each oscillation takes 10–30 seconds initially, with the period increasing as reactants are consumed.

Nettoyage

The spent solution contains iodine and manganese. Collect in inorganic waste. Rinse all glassware. Clean the magnetic stir bar.

Détails

Catégorie
Classroom Demonstrations
Difficulté
Advanced (University)
Durée
40 min
Coût estimé
$20,00
Étapes
7
Matériaux
7

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Frequently Asked Questions

What is the objective of Réaction Oscillante de Briggs-Rauscher?
Observer une réaction chimique oscillante qui cycle répétitivement entre trois états de couleur distincts, démontrant la cinétique chimique non linéaire.
How difficult is Réaction Oscillante de Briggs-Rauscher?
This experiment is rated as Advanced (University). It takes approximately 40 minutes to complete.
What safety precautions are needed for Réaction Oscillante de Briggs-Rauscher?
Key safety precautions include: 30% H₂O₂ causes burns — handle with extreme care; H₂SO₄ is corrosive; KIO₃ is an oxidizer.
What materials are needed for Réaction Oscillante de Briggs-Rauscher?
The main materials required are: Potassium iodate (KIO₃), Malonic acid (CH₂(COOH)₂), Manganese(II) sulfate (MnSO₄), Starch solution (1%), Hydrogen peroxide (30%).
What results should I expect from Réaction Oscillante de Briggs-Rauscher?
The solution oscillates between colorless, amber, and deep blue 10–15 times before settling to a permanent dark blue. Each oscillation takes 10–30 seconds initially, with the period increasing as reactants are consumed.