Chemiluminescence: A Laboratory Activity for Halloween
Source: Shakishiri, Bassam Z., Chemical Demonstrations, Volume 1. The University of Wisconsin Press, Madison, Wisconsin, 1983, pp.156—167.
Abstract: This experiment will show how luminol emits glowing light as it is oxidized by various substances, and to observe the same behavior in methyl salicylate crystals when crushed.
Introduction: Many combustion reactions produce light by thermal means. These reactions release sufficient thermal energy to heat the reaction mixture to incandescence. Other reactions release energy at room temperature. This exothermic production of visible light by a chemical reaction is called chemiluminescence. When a reaction of this nature occurs in living organisms, it is called bioluminescence. The most familiar example of such an organism is the firefly. In a biochemical reaction within the body of this insect, light is produced by the action of an enzyme on the substrate luciferin. Other organisms producing bioluminescence are certain bacteria, algae, coelenterates (the sea pansy) and crustaceans such as the cypridna. Chemiluminescence occurs when an energy—releasing reaction produces a molecule in an electronically excited state and that molecule, as it returns to the ground state, releases its energy as a photon of light. Lightning exemplifies gas—phase chemiluminescence. When an electrical discharge occurs in the atmosphere, gas molecules, such as N2 and O2 are excited from the ground state to higher energy levels. In addition, N, O and other atoms are produced. The recombination of these atoms into molecules, as well as the return of excited—state molecules to the ground state, releases energy in the form of visible light. Chemiluminescence also occurs in the liquid and solid phases, as illustrated by the following laboratory procedure.
The chemiluminescent process is distinctly different from the photoluminescent processes fluorescence and phosphorescence, both of which occur after the excited state of a molecule is produced from its ground state by the absorption of light energy. Thus fluorescent species emit light only while being irradiated. Phosphorescent species may appear to emit light without being irradiated, but this emitted energy had to have been absorbed at an earlier time. Chemiluminescent reactions, however, produce light without any prior absorption of radiant energy.
Another phenomenon known as triboluminescence is the emission of light energy when a mechanical stress is applied to a crystal. As the crystal is stressed by applying pressure or torque. This phenomena is explored in Part B.
2 400 mL beakers (for mixing solutions A and B)
1 250 mL beaker (the reaction vessel)
2 25 or 50 mL graduated cylinders (for measuring solutions A and B)
1 10 mL graduated cylinder (for the 3% H2O2)
Solution A: prepare by dissolving approx. 0.1 g. luminol and 1 g. NaOH in 250 mL water.
Solution B: prepare by dissolving 2.5 g. K3Fe(CN)6 (potassium ferricyanide) in 250 mL water, then adding
5 mL 3% H2O2(hydrogen peroxide).
A pinch of fluorescein FIGURATIVELY SPEAKING — DO NOT TOUCH!!!
A few drops of phenolphthalein solution (in dropper bottles – please share nicely!)
A few pieces of wintergreen candy (methyl salicylate crystals)
**Construct the appropriate data tables in your lab notebook to record the necessary data.**
Procedure: Part A
1. Carefully make solutions A and B as directed. Label the beakers. When you are finished, let your instructor know that you are ready for lights out. You have enough of the solutions to repeat a step if you want.
2. Measure equal amounts of each solution ( about 25—50 mL each)into the graduate cylinders.
3. Simultaneously pour the solutions into the third beaker and swirl it gently. Record your observations. (Oooohhh, aaaahhh!) Dump the solution ( save a bit in a test tube if you wish) and rinse the beaker well.
4. Add a pinch of fluorescein to about 20 mL of water in the beaker, then repeat steps 2 and 3. Record your observations. Dump and rinse out the beaker.
5. Put 20 mL water in the beaker and add a few drops of phenolphthalein. Repeat steps 2 and 3. Record your observations.
6. Clean up and be sure to wash your hands well.
Procedure Part B:
1. Get a few pieces of life savers and go to a dark corner with your lab partner (!!!!!!!)
2. Holding the candy between your teeth or in a pair of pliers, bite down hard while your partner watches carefully for tiny flashes of blue light.
3. Record your observations.
Questions: (to be answered in your lab book)
1. Define: a. chemiluminescence.
2. Distinguish between the energy source that provides the initial photon for the light emitted during a flame test and the source of energy in chemiluminescence and triboluminescesce.
3. The prefix chemi— means that a _____________ _____________ produced the excited atom. The prefix photo— means that __________ produced the excited atom.
4. Distinguish between the chemiluminescent process and the photoluminescent process.
Summary and Conclusions:
Write a paragraph describing what you observed.