22.15 The IO₃^-/I₂ Catalyzed Decomposition of H₂O₂

Chemical Concept Demonstrated: Catalytic decomposition

Demonstration:

The beaker contains the following solutions: Starch Solution Solution A: KIO3 and H2SO4 dissolved in water. Solution B: malonic acid and MnSO4 dissolved in water. Solution C: 30% H2O2 dissolved in water.

Observations:

    The color sequence goes from deep blue to colorless to yellow to gold to brown to deep blue again.

Explanation (including important chemical equations):

    The first primary step in this reaction is the oxidation of hydrogen peroxide by iodic acid:

        5 H₂O₂ (aq) + 2 HIO₃ (aq) --> 5 O₂ (g) + I₂ (aq) + 6 H₂O (l)

    The second step is the oxidation of of iodine by hydrogen peroxide:

        5 H₂O₂ (aq) + I₂ (aq) --> 2 HIO₃ (aq) + 4 H₂O (l)

    The overall result is a decomposition of H₂O₂ into H₂O and O₂.  The higher the initial concentrations, the shorter the induction period.

    The movie from demonstration 22.14 is included because of the similarity of the concepts demonstrated.