Réaction de l'Horloge à Iode

Une réaction minutée qui vire soudainement au bleu foncé après un délai prévisible

Classroom Demonstrations Intermediate (High School) 45 min ~$10,00

Objectif

Démontrer la cinétique réactionnelle et l'effet de la concentration et de la température sur la vitesse de réaction à l'aide de la réaction de l'horloge à iode.

Contexte

The iodine clock reaction is a classic demonstration of chemical kinetics. Two colorless solutions are mixed and after a predictable delay, the solution suddenly turns dark blue. The delay occurs because bisulfite (HSO₃⁻) rapidly reduces any I₂ produced back to I⁻ (the clock mechanism). When all the bisulfite is consumed, I₂ accumulates and reacts with starch to produce the dramatic blue-black color. By varying concentration or temperature, students can explore factors affecting reaction rate.

Avertissements de sécurité

  • H₂SO₄ is corrosive
  • NaHSO₃ releases SO₂ gas if over-acidified — work in ventilated area
  • KIO₃ is an oxidizer
  • Hot plate surfaces are a burn hazard

EPI requis

goggles gloves lab_coat

Matériaux

  • Potassium iodate (KIO₃) (2 g)
    Solution A
  • Sodium bisulfite (NaHSO₃) (1 g)
    Solution B
  • Starch solution (1%) (10 mL)
    Indicator in Solution B
  • Sulfuric acid (0.5M H₂SO₄) (20 mL)
    Solution A acidification
  • Distilled water (500 mL)

Équipement

Beakers (250 mL, 4) Magnetic stirrer Stopwatch Thermometer Graduated cylinders Hot plate Ice bath

Procédure

1

Prepare Solution A: Dissolve 2 g KIO₃ in 200 mL water, add 20 mL of 0.5M H₂SO₄.

5 min
2

Prepare Solution B: Dissolve 1 g NaHSO₃ in 200 mL water, add 10 mL of 1% starch solution.

5 min
3

Trial 1 (baseline): Mix 50 mL of A with 50 mL of B and start the stopwatch immediately. Record the time until the solution turns blue.

5 min
4

Trial 2 (concentration effect): Mix 25 mL of A + 25 mL water with 50 mL of B. Record the time. It should take approximately twice as long.

7 min
5

Trial 3 (temperature effect): Warm both solutions to 40°C. Mix 50 mL of each and record the time. It should be significantly shorter.

8 min Handle warm solutions carefully
6

Trial 4 (cold): Cool both solutions to 10°C in an ice bath. Mix and record the time.

8 min
7

Plot reaction time vs. concentration and temperature. Discuss rate law, activation energy, and the Arrhenius equation.

7 min

Résultats attendus

The blue color appears suddenly after a delay of 5–60 seconds depending on conditions. Doubling concentration roughly halves the time. Increasing temperature by 10°C roughly halves the time (consistent with the Arrhenius equation).

Nettoyage

Pour reacted solutions down the drain with water. Rinse all glassware. Clean the magnetic stirrer.

Détails

Catégorie
Classroom Demonstrations
Difficulté
Intermediate (High School)
Durée
45 min
Coût estimé
$10,00
Étapes
7
Matériaux
5

Plus d'expériences

Bécher Invisible (Correspondance d'Indice de Réfraction) 15 min Chimioluminescence avec le Luminol 30 min Colonne Arc-en-ciel de Densités 30 min Congélation Instantanée : Eau Surfusionnée 120 min Dentifrice d'Éléphant 20 min Fluide Non Newtonien : Oobleck 20 min Magnésium Brûlant dans la Glace Carbonique 25 min Réaction du Sodium avec l'Eau 25 min Réaction Oscillante de Briggs-Rauscher 40 min Réaction Thermite 30 min

Frequently Asked Questions

What is the objective of Réaction de l'Horloge à Iode?
Démontrer la cinétique réactionnelle et l'effet de la concentration et de la température sur la vitesse de réaction à l'aide de la réaction de l'horloge à iode.
How difficult is Réaction de l'Horloge à Iode?
This experiment is rated as Intermediate (High School). It takes approximately 45 minutes to complete.
What safety precautions are needed for Réaction de l'Horloge à Iode?
Key safety precautions include: H₂SO₄ is corrosive; NaHSO₃ releases SO₂ gas if over-acidified — work in ventilated area; KIO₃ is an oxidizer.
What materials are needed for Réaction de l'Horloge à Iode?
The main materials required are: Potassium iodate (KIO₃), Sodium bisulfite (NaHSO₃), Starch solution (1%), Sulfuric acid (0.5M H₂SO₄), Distilled water.
What results should I expect from Réaction de l'Horloge à Iode?
The blue color appears suddenly after a delay of 5–60 seconds depending on conditions. Doubling concentration roughly halves the time. Increasing temperature by 10°C roughly halves the time (consistent with the Arrhenius equation).