Iod-Uhr-Reaktion

Eine zeitgesteuerte Reaktion, die nach einer vorhersehbaren Verzögerung plötzlich dunkelblau wird

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

Ziel

Reaktionskinetik und den Einfluss von Konzentration und Temperatur auf die Reaktionsgeschwindigkeit mithilfe der Iod-Uhr-Reaktion demonstrieren.

Hintergrund

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.

Sicherheitswarnungen

  • 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

Erforderliche PSA

goggles gloves lab_coat

Materialien

  • 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)

Ausrüstung

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

Durchführung

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.

Erwartete Ergebnisse

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).

Aufräumen

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

Details

Kategorie
Classroom Demonstrations
Schwierigkeit
Intermediate (High School)
Dauer
45 Min.
Geschätzte Kosten
$10,00
Schritte
7
Materialien
5

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Frequently Asked Questions

What is the objective of Iod-Uhr-Reaktion?
Reaktionskinetik und den Einfluss von Konzentration und Temperatur auf die Reaktionsgeschwindigkeit mithilfe der Iod-Uhr-Reaktion demonstrieren.
How difficult is Iod-Uhr-Reaktion?
This experiment is rated as Intermediate (High School). It takes approximately 45 minutes to complete.
What safety precautions are needed for Iod-Uhr-Reaktion?
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 Iod-Uhr-Reaktion?
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 Iod-Uhr-Reaktion?
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).