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The Chemiluminescent Clock Reaction

 

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.

chemcloc.gif

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)43- 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.

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