Chemiluminescent Chemical Reactionsin a Model Volcano

Introduction

Try this amazing demonstration! Construct a model volcano using polyurethane foam, and then produce a fiery lava flow with the decomposition of hydrogen peroxide and lightstick chemicals. An awesome display of chemical reactions simulating a volcanic eruption!

Concepts

• Polymers
• Catalysis
• Chemiluminescence
• Decomposition reaction

Materials

Safety Precautions

Perform this reaction only in an operating fume hood. Parts A and B of polyurethane foam system may contain skin and tissue irritants. Avoid breathing any vapors produced and avoid skin contact. This reaction also produces a great deal of heat so it is imperative that an insulating material, such as a Pyrex tray, be placed under the volcano. Do not scale this reaction up. Wear chemical splash goggles, a chemical-resistant apron and chemical-resistant gloves. All students must wear chemical splash goggles while observing the demonstration. Follow all laboratory safety guidelines and wash hands thoroughly with soap and water before leaving the laboratory.

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. If the procedure was carried out without any glass from the light stick being transferred into the flask, the leftover product mixture may be washed down the drain with plenty of water according to Flinn Suggested Disposal Method #26b. If glass was introduced into the Erlenmeyer flask, the mixture should be filtered or decanted to remove any possible broken glass pieces. Any glass should be placed into a broken glass container. Once the glass is removed the remaining solution may be washed down the drain with plenty of water according to Flinn Suggested Disposal Method #26b. The solid products of this reaction may be disposed of in a landfill according to Flinn Suggested Disposal Method #26a.

Prelab Preparation

Volcano Model—Polyurethane Foam Reaction

1. Take a large, marble-sized piece of clay and roll it out into a thin rope.
2. Place the thin clay rope around the bottom edge of a 10-ounce plastic cup.
3. Place the cup upside down on the table and carefully press a 18" x 16" piece of aluminum foil on the bottom of the cup with the clay. Make sure to center the foil (see Figure 1).
   {12158_Preparation_Figure_1}
4. Invert the cup with the foil and place it into a wide, cone-shape mold large enough to fit the cup. The opening of the cup should be level with opening of the large cone (see Figure 2).
   {12158_Preparation_Figure_2}
5. Place the cone into a 300-mL beaker to hold the party hat steady.
6. Press the aluminum foil firmly against the walls of the hat (see Figure 2).
7. In a fume hood or well-ventilated area, pour approximately 20 mL of liquid Part A (polyurethane foam system) into a disposable cup.
8. Note: The exact volume is not critical. Do not use glassware! It is impossible to remove the hardened foam. Please use only disposable materials for the handling and mixing of polyurethane foam.
9. Place approximately 20 mL of liquid Part B into a second disposable cup. Note: The volume of Part B should be equal to that of Part A.
10. In the cup containing Part A, add 1 drop each of red, green and blue food dye. Stir the mixture with a wooden splint until the color is uniform. The color will be dark reddish brown.
11. Pour the contents from cup B into the cup containing Part A. Mix well—the components will begin to react.
12. As the mixture reacts, pour the mixture between the plastic cup and the foil in the cone-shaped mold. Carefully distribute the reacting polyurethane foam around the cup to create a level volcano (see Figure 2).
13. Allow the polyurethane foam to completely react. It will become hot. Caution: Do not touch the foam until it hardens.
14. Once the foam has fully reacted and has cooled down (approx. 10–15 minutes), remove the mold and the aluminum foil from the polyurethane foam (see Figure 3). Cut a small opening at the bottom edge of the model to insert tubing.
    {12158_Preparation_Figure_3}
15. Using scissors or a utility knife, carefully cut a hole in the bottom of cup. Remove enough so that the top of a 125-mL wide-mouth Erlenmeyer flask fits just level with the bottom of the cup.
16. If desired, remove the clay from around the edge of the cup (see step 2).

Procedure

Decomposition of Hydrogen Peroxide—Chemiluminescence

1. Set up all reactants and equipment for the volcano reaction in a fume hood.
2. Measure 30 mL of 6% hydrogen peroxide in a 50-mL graduated cylinder and pour into a 125-mL Erlenmeyer flask.
3. Add approximately 3 mL of liquid soap into the Erlenmeyer flask.
4. Add approximately 1 mL of red food dye into the flask.
5. Swirl to mix.
6. Activate the yellow lightstick by bending it until a cracking sound is heard.
7. Mix the contents inside the lightstick by mild shaking.
   {12158_Procedure_Figure_4}
8. Using heavy duty scissors or utility knife, carefully cut open the light stick at one end and add the liquid contents to the 125-mL Erlenmeyer flask. Note: The light stick contains a glass ampule which, if possible, should be left in the light stick.
9. In a 50-mL beaker, add 30 mL of distilled water and 0.6 g of yeast. Mix to dissolve. Note: Prepare fresh for best results.
10. Obtain a 24-inch piece of latex tubing and attach one end to a 30-mL syringe.
11. Suction all the yeast solution into the syringe and set the syringe aside.
12. The polyurethane mountain, Erlenmeyer flask and the syringe of yeast solution must be in a chemical fume hood. Place the setup on a demonstration tray.
13. Place the mountain over the top of the Erlenmeyer flask.
14. Carefully place the latex tubing attached to the syringe inside the Erlenmeyer flask and under the volcano model. Note: Do not press on the syringe (see Figure 4).
15. Press the syringe to add the yeast catalyst to the hydrogen peroxide mixture. Stand back and enjoy as glowing red-orange lava oozes from the volcano and flows down the mountain.

Student Worksheet PDF

12158_Student.pdf

Teacher Tips

• Prepare a party hat-shaped cone using the cardstock provided in the kit.
• Darken the room for best results. For more luminescence, two light sticks may be used.

Answers to Questions

1. Describe what happened in this demonstration. Include all observations about the substance produced.

   A liquid was added to the volcano and viscous red-orange glowing “lava” flowed out of the volcano and down the side of the mountain.

2. Write the chemical equation for the decomposition of hydrogen peroxide.

   2H₂O₂(aq) → 2H₂O(g) + O₂(g)

3. What is chemiluminescence?

   Chemiluminescence is light energy that is released from molecules that have gained chemical energy.

Discussion

The mountain is constructed with polyurethane foam. There are many forms of polyurethane such as fibers, coatings, elas-tomers, flexible foams and rigid foams. The foam in this system is a rigid foam that is used in furniture, insulation, flotation devices, and many other items. The rigid polyurethane foam is produced by mixing equal parts of two liquids, called Part A and Part B. This lightweight foam expands to about thirty times its original liquid volume and will become rigid in about five minutes.

Part A is a viscous, cream-colored liquid containing a polyether polyol, a silicone surfactant, and a catalyst. The polyether polyol contains reactive hydroxyl (–OH) end groups. The silicone surfactant reduces the surface tension between the liquids. The catalyst is a tertiary amine which aids in speeding up the reaction without being chemically changed itself. Part B is a dark brown viscous liquid containing diisocyanate and higher oligomers (dimers, trimers or tetramers). When the polyether polyol (Part A) is mixed with the diisocyanate (Part B), an exothermic polymerization reaction occurs, producing polyurethane (see Equation 1).

During the course of the polymerization reaction, a small amount of water reacts with some of the diisocyanate. A decomposition reaction occurs and produces carbon dioxide gas, thus causing the solution to foam and expand in volume. Pores in the mixture are created from the gas; these pores are visible when looking at the rigid substance. The multifunctionality of both reactants leads to crosslinking in the polymer, causing it to become rigid within minutes (see Equation 2).

The final hot lava flow is the result of the catalytic decomposition of hydrogen peroxide mixed with soap, food coloring and a chemiluminescent dye. The catalyst is the yeast which speeds up the decomposition of the hydrogen peroxide. The decomposition of hydrogen peroxide produces steam and oxygen gas. The oxygen gas and water vapor cause the dishwashing liquid foam. The lightstick mixture is added to the reaction mixture to create the chemiluminescent orange glow. A lightstick is a chambered vessel containing two sections. The outside of the light stick is semipliable plastic and inside the plastic tube are two different reactants. To prevent the chemical reaction from occurring until desired, one reactant is put inside a glass ampoule. Individual commercial formulations vary but the two reactants are hydrogen peroxide and a phenyl oxalate compound such as trichlorophenyl oxalate (TCPO) with a fluorescent dye. To activate a lightstick the tube is flexed (see Figure 5). The outer plastic tube material is semipliable but the inner glass ampoule is not and breaks. The distinctive noise heard upon activating a light stick is the inner glass breaking. Upon mixing, TCPO reacts with the hydrogen peroxide producing trichlorophenol, carbon dioxide and energy (see Equation 3). The energy released in the reaction is from the decomposition of an unstable, high-energy intermediate, C₂O₄. The dye molecules harness this reaction’s energy elevating the dye molecules to an excited state. The chemical energy produced in the reaction is then transformed into light energy. The dye releases the energy by the emission of light. Chemiluminescence is defined as light energy that is released from molecules that have gained chemical energy. Dyes used in commercial light sticks have a light emission wavelength in the visible range so that they may be seen. In the military, light sticks use dyes that may release light emissions in the visible and infrared ranges.

The light-producing reaction that occurs in a lightstick.