Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Prepare Solution A by adding 0.05 g of luminol and 25 mL of 5% sodium hydroxide solution to approximately 400 mL of distilled or deionized (DI) water. Stir to dissolve the luminol. Once dissolved, dilute this solution to a final volume of 500 mL with DI water.
2. Prepare Solution B by adding 0.3 g of potassium ferricyanide and 8 mL of 3% hydrogen peroxide to approximately 400 mL of DI water. Stir to dissolve the potassium ferricyanide. Once dissolved, dilute this solution to a final volume of 500 mL with DI water.
3. Set up the demonstration equipment as shown in Figure 2.
   {12285_Preparation_Figure_2}

Safety Precautions

Hydrogen peroxide is an oxidizer and skin and eye irritant. Sodium hydroxide solution is corrosive, very dangerous to eyes and skin burns are possible. Much heat is evolved when sodium hydroxide is added to water. If heated to decomposition or in contact with concentrated acids, potassium ferricyanide may evolve poisonous hydrogen cyanide fumes. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.

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 resulting solutions may be disposed of according to Flinn Suggested Disposal Method #26b.

Teacher Tips

• Enough materials are provided in this kit for 30 students working in pairs, or for 15 groups of students. This laboratory activity can reasonably be completed in one 50-minute class period.
• Pour the two solutions into a “Cool Light Spiral Apparatus” to increase the surface area over which light is emitted and increase the visual impact! To make your own “Cool Light Spiral Apparatus”, attach a small piece of plastic tubing, a glass elbow, and a long piece of plastic tubing to the funnel stem (see Figure 3). Insert this setup into a long, Plexiglas^® tube. Drill a hole in the Plexiglas tube just below the height of the glass elbow connected to the funnel stem. Thread the long plastic tubing through this hole from the inside out. Wind the tubing around the Plexiglas tube. Drill a hole in the Plexiglas tube about 1" above the height of the collecting vessel. Feed the coiled tubing through the hole and attach it to another glass elbow and a small piece of plastic tubing. If the tubing does not stay tightly coiled, a small amount of quick-drying glue can be used to keep it in place. Insert the plastic tubing into the collecting vessel. If the spiral you build is tall, we recommend that some sort of support stand is used or that it is attached to a ring stand for stability and safety.
  {12285_Tips_Figure_3}
  Another means of displaying luminol’s luminescence is to take the two solutions (A and B), place them in spray bottles, and spray them at each other creating a luminescent cloud. The key to this procedure is to get the solutions into as fine a mist as possible. Caution: Do not spray the solutions toward anyone or in a manner in which they can be easily inhaled.
• Use only distilled or deionized water when preparing the solutions. Hard water and softened water contain high concentrations of ions (such as chloride ions) that may interfere with the excited state of the luminol and prevent chemiluminescence.

References

Harvey, E. N., A History of Luminescence. The American Philosophical Society: Philadelphia, PA, 1957; p 5.

Huntress, E. H.; Stanley, L. N.; Parker, A. S., J. Chem. Educ., 1934, 11, 145.

Shakhashiri, B. Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry, Vol. 1; University of Wisconsin: Madison, 1985; p 189.

Introduction

Chemiluminescence demonstrations are popular with students and teachers alike. This kit demonstrates basic chemiluminescence using luminol.

Concepts

• Chemiluminescence
• Oxidation–reduction
• Catalyst

Background

Down through the past several centuries there has been great expansion in the knowledge about materials, organic and inorganic, that produce light (luminescence). There are at least six different classifications of light-producing systems that have been observed. One of these is known as chemiluminescence; light produced through a chemical reaction, whether in a gas or in solution. The energy for light emission comes from a chemical reaction, usually involving considerable change in the composition of the chemiluminescent material. The appearance of colors when different metal salts are placed in the flame of a Bunsen burner are examples of a variation of chemiluminescence known as pyroluminescence. One of the long-standing classic models of a chemiluminescent reaction is the glow of solid phosphorus in air. This is an oxidation reaction in which light is produced and some heat. Out of a wide variety of “cool light” demonstrations, where little or no heat is produced, the use of luminol (3-amino-phthalhydrazide) has been one of the most popular (see Figure 1).

Luminol was discovered to be luminescent by Albrecht in 1928. Since that time numerous procedures have been developed that produce light using luminol. Experimentation has demonstrated that for luminol to luminesce, an oxidizing agent, an alkaline pH, and some type of catalyst (such as copper or iron compounds) are required. This procedure gives just that condition. Sodium hydroxide acts as a base and converts luminol into a dianion which is oxidized by hydrogen peroxide to an aminophthalate ion. The aminophthalate is found in an excited state which will decay to a lower energy state through chemiluminescence and one of the products is the emission of light. This light has a wavelength of 425 nm which is in the blue zone of the visible spectrum.

This “Cool Light” laboratory activity has value not only for the obvious reason of demonstrating chemiluminescence, but it can also be used to show the effects of a catalyst, the effect of pH on a reaction, the effect of temperature on a reaction and how reaction rates are affected by concentration.

Materials

Safety Precautions

Hydrogen peroxide is an oxidizer and skin and eye irritant. Sodium hydroxide solution is corrosive, very dangerous to eyes, and skin burns are possible. Much heat is evolved when sodium hydroxide is added to water. If heated to decomposition or in contact with concentrated acids, potassium ferricyanide may evolve poisonous hydrogen cyanide fumes. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron.

Procedure

1. Turn down the lights. The room should be as dark as possible.
2. Pour Solution A and Solution B into the large funnel simultaneously. As the two solutions mix, chemiluminescence begins.
3. As the reaction progresses, it can be enhanced by adding small amounts of potassium ferricyanide and 5–10 mL of 5% sodium hydroxide solution into the flask.