- A slice of potato or liver, drops of catalase enzyme (or prick your finger and use your own blood), a small quantity of MnO2, a clean nail and a rusty nail are all added to different crystallizing dishes containing 30% H2O2.
Chemical Concepts Demonstrated: Chemisty of hydrogen peroxide, disproportation reactions, enzyme catalysis
Demonstration:
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Observations:
The various items foam in the dishes.
Explanation (including important chemical equations):
Hydrogen peroxide undergoes disproportionation. Both oxidation and reduction occur at the same time.
2 H2O2 (aq) ---> 2 H2O (l) + O2 (g) enthalpy: -196.1 kJ/mol
The activation energy of the reaction is about 75 kJ/mol in the absence of catalyst. Platinum metal catalysts can lower the activation energy to about 49 kJ/mol. The catalase enzyme (found in blood) lowers the activation energy to below 8 kJ/mol, which corresponds to an increase in the rate of reaction at physiologial temperatures by a factor of 2 x 10 11 or more.