The Chemiluminescent Clock Reaction

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Chemical Concepts Demonstrated

Chemiluminescence
Chemical kinetics

Demonstration

The 4 beakers contain 4 solutions in varying amounts.

The solutions are poured into the beakers simultaneously.

Solution A: Luminol dissolved in NH₃ and diluted.
Solution B: K₃Cu(CN)₄ dissolved in water
H₂O₂
water

All the beakers contain the same amount of Solutions A and B. Beaker 4 contains the least amount of H₂O₂ and the most water, beaker 1 contains the least amount of water and the most H₂O₂, and the remaining two beakers have amounts in a relative series to these two.

Observations

The four beakers begin to glow in a specific order.

Explanation

The mechanism for this reaction is not well known. However, it is believed that it involves the oxidation of the Cu(CN)₄^3-complex ion to Cu²⁺, which then forms an amine complex that catalyzes the oxidation of luminol by hydrogen peroxide.

Despite the uncertainties regarding the mechanism, this demonstration is still useful for qualitative analyses of chemical kinetics and chemiluminescence.

Contributors

Dr. George Bodner (Perdue University)