Light Rope

Chemiluminescence Demonstration

Introduction

Use a light necklace to demonstrate the effect of temperature on a reaction rate.

Concepts

  • Chemiluminescence
  • Reaction rate

Materials

Ice water
Warm water, temperature over 50 °C
Beakers, 250-mL, 3
Chemiluminescent necklace
Graduated cylinders, 100-mL, 2

Safety Precautions

Do not break open the light necklace. The solution will burn your eyes if it somehow gets into them!

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The used necklace may be disposed of in the trash.

Procedure

  1. Activate the necklace by bending and shaking the plastic tube.
  2. Fill one graduated cylinder with hot water.
  3. Fill one graduated cylinder with ice water.
  4. Place about 6 inches of the necklace into each cylinder.
  5. Turn out the lights. Observe where the light brightens on the light necklace, where it doesn’t change, and where it dims.
  6. If a light meter is available, it can also be used to measure the glow intensity.

Teacher Tips

  • The necklace may be placed in the freezer and will last for several weeks.

Discussion

The light necklace contains dilute hydrogen peroxide in a glass ampule, a solvent of diphenyloxalate ester, along with an organic dye.

When the ampule is crushed, the ester is oxidized by the hydrogen peroxide

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An intermediate (I) is formed during this reaction.
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This intermediate reacts with the dye, producing 2CO2 molecules, and releasing energy to the dye molecule.
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The dye then relaxes to its ground state releasing this energy in the form of light.

This reaction rate is directly related to temperature. As the temperature of reactants is increased, the reaction speeds up and a more intense chemiluminescence is observed.

References

Special thanks to John Mauch, chemistry teacher, Pasco High School, Pasco, Washington, who provided us with the instructions for this activity.

Salter, C.; Salter, G; Range, K. J. Chem Educ., 1999, 76, pp 84–85.

Shakhashiri, B. Z. Chemical Demonstrations: A Handbook for Teachers in Chemistry; University of Wisconsin: Madison, 1983, Vol. 1, pp 146–152.

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