Chemystery of Halloween

Introduction

The purpose of the following series of demonstrations is to illustrate that “black magic” has a scientific basis. The demonstrations are adaptable for multiple class levels. These demonstrations also create an opportunity to introduce some new concepts that will be studied in more depth later in the year.

Setting the stage: Put on a witch or wizard costume (after all—who were the first chemists?) and spooky music. Darken the room and shine a spotlight or black light on your demonstration table.

Concepts

• Exothermic reactions
• Catalysts
• Decomposition reactions
• Polymers
• Physical and chemical change
• Chemiluminescence
• Oxidation–reduction
• Triboluminescence
• Cross-link
• Fluorescence

Experiment Overview

Demonstration I. Ghosts and Goblins
When manganese dioxide is dropped into a bottle containing 30% hydrogen peroxide, a “ghost” appears in the form of water vapor and oxygen.

Demonstration II. Amorphous Monster
Create an amorphous monster by mixing two liquids together. The mixture expands to about 30 times its original volume and results in a hardened, lightweight polyurethane foam.

Demonstration III. Oozing Pumpkin Head
Place a beaker of green solution inside a plastic pumpkin, chant an incantation while you add a yellow liquid and stand back! Foamy ooze and steam will erupt out of the pumpkin’s eyes and nose.

Demonstration IV. Eerie Lights
Now create an eerie light show. Combine two solutions to produce a beautiful chemiluminescence which will last approximately 10 minutes.

Demonstration V. More Eerie Lights
Exhibit an even brighter display of triboluminescence that resembles lightning.

Demonstration VI. Fluorescent Slime Monster
Add a clear solution, two powders, a little water to create a fluorescent version of the “Blob.”

Demonstration VII. Silly Putty–Type Slime
Make a silly putty–type slime and test its propertiWhite glue consists of a polyvinyl acetate polymer dissolved in

Materials

Safety Precautions

Manganese dioxide is a strong oxidant; avoid contact with organic material; body tissue irritant. Thirty percent hydrogen peroxide will act as an oxidizer with practically any substance; severely corrosive to skin, eyes and respiratory tract; a very strong oxidant; a dangerous fire and explosion risk. Do not heat hydrogen peroxide. Demonstration II should be performed in a fume hood or well-ventilated area. Avoid breathing any vapor produced and avoid skin contact as both Part A and Part B contain skin and tissue irritants. Hydrogen peroxide, 30%, will act as an oxidizing agent with practically any substance. This substance is severely corrosive to the skin, eyes and respiratory tract; a very strong oxidant; and a dangerous fire and explosion risk. Do not heat this substance. Sodium iodide is slightly toxic by ingestion. Although the dishwashing liquid is considered nonhazardous, do not ingest the material. Do not stand over the reaction; steam and oxygen are produced quickly. While the 3% solution of hydrogen peroxide used in Demonstration IV is very weak, it is still an oxidizer and a skin and eye irritant. Potassium ferricyanide solution is a mild irritant. Contact with strong acids may liberate toxic hydrogen cyanide gas; avoid contact with strong acids. Demonstration V is considered nonhazardous. Follow all standard laboratory safety guidelines. Wash hands thoroughly if they come in contact with the fluorescent slime. Slime is generally considered nonhazardous; however, it should not be ingested and should only be used in the manner intended. It is not recommended that students be allowed to take slime home. Slime will easily stain clothing, upholstery and wood surfaces. With food coloring added, it will stain these surfaces and skin even more readily. The fluorescein/bromphenol blue dye may be irritating to the skin. Wash hands thoroughly after handling the Silly Putty–type material.Generally nonhazardous, it should not be ingested. It is not recommended that students be allowed to take their silly putty home. The putty will easily stain clothing, upholstery and wood surfaces. If food coloring is added, it will stain these surfaces even more readily. Wash hands thoroughly with soap and water before leaving the laboratory. 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. Tissue and thread from Demonstration I may be placed in the trash. The contents of the liter bottle may be rinsed down the drain with excess water according to Flinn Suggested Disposal Method #26b. Rinse the bottle out thoroughly and dispose of it in the trash according to Flinn Suggested Disposal Method #26a. For Demonstration II, mix together liquid Parts A and B, allow them to react, then dispose of the foam in the trash according to Flinn Suggested Disposal Method #26a. The foam and solution left in the beaker and pumpkin in Demonstration III may be disposed of according to Flinn Suggested Disposal Method #26b. The resulting solution in Demonstration IV may be flushed down the drain with copious amounts of water according to Flinn Suggested Disposal Method #26b. Dispose of the slime from Demonstration VI in an approved landfill site according to Flinn Suggested Disposal Method #26a. The Silly Putty–type materials from Demonstration VII may be disposed of in the trash according to Flinn Suggested Disposal Method #26a.

Prelab Preparation

Demonstration I. Ghosts and Goblins

1. Place approximately 5 g (½ teaspoon) of manganese dioxide in a small square of soft tissue paper.
2. Tie the tissue with a piece of thread leaving a long tail. Make sure the tissue is tied so that the manganese dioxide will not spill out.
3. Using the graduated cylinder, measure out 40 mL of 30% hydrogen peroxide and pour it into a clean, colored 1-liter plastic soft drink bottle.
4. Suspend the manganese dioxide sack above the hydrogen peroxide. (The label and color of the bottle should hide the tissue paper sack and thread from student view.) Wedge the thread in position by loosely inserting a one-hole stopper in the bottle.

Demonstration IV. Eerie Lights

1. Add 70 mL of the 0.6% potassium ferricyanide solution and 7 mL of 3% hydrogen peroxide solution to one 250-mL beaker.
2. Add 70 mL of the Energetic Light solution to a second 250-mL beaker. Note: The Energetic Light solution is very viscous.

Procedure

Demonstration I. Ghosts and Goblins

1. When you are ready for the ghosts to appear, remove the stopper and the manganese dioxide will fall into the hydrogen peroxide, thus catalyzing the release of oxygen and steam.
2. Stand back! Do not touch the bottle until it has fully cooled and the reaction has ceased! Ghosts and goblins of bygone years will rise from the bottle and flow into the room. The heat evolved causes the bottle to shrink “when the ghosts leave.” This nice side-effect is created by a heat-induced rearrangement of the bonds in the plastic bottle.

Demonstration II. Amorphous Monster

1. Fill a Styrofoam cup about ⅛ full of liquid Part A. Add a couple of drops of food coloring, if desired, and stir using the tongue depressor or stirring rod.
2. Add liquid Part B to the same cup until the cup is about ¼ full.
3. Thoroughly mix the solution and place the cup containing the solutions on a paper towel.
4. Use the spotlight. Mutter an incantation. Nothing happens! Try again. Still nothing happens! Move on to the next demonstration—and the blob appears!

Demonstration III. Oozing Pumpkin Head

1. Place the plastic pumpkin in a plastic tray that is several inches deep.
2. Using a 100-mL graduated cylinder, measure out 70 mL of the 30% hydrogen peroxide and add to the 250-mL beaker. Rinse the graduated cylinder thoroughly.
3. Measure 10 mL of dishwashing liquid into the 10-mL graduated cylinder and add it to the beaker containing the hydrogen peroxide. Add a few drops of green food coloring, if desired, and stir. Place the beaker inside the pumpkin.
4. Measure 5 mL of 2 M sodium iodide solution using a clean 10-mL graduated cylinder.
5. Tell students you will now call forth the evil spirit of the “Great Pumpkin.”
6. Quickly, but carefully, add the sodium iodide to the 250-mL beaker inside the pumpkin.
7. Immediately cover the top of the pumpkin with the 6" x 6" square. Hold the square in place with a hand or weight.
8. Watch as the “spirit” erupts from the eyes and nose.

Demonstration IV. Eerie Lights

1. Darken the room completely.
2. While stirring with a stirring rod, add the potassium ferricyanide/hydrogen peroxide solution to the Energetic Light solution.
3. Observe the chemiluminescence. Stir the solution occasionally to prolong the reaction.

Demonstration V. More Eerie Lights

1. Hand each student one Wint-O-Green Lifesavers^®.
2. Darken the room. Allow sufficient time for students’ eyes to adapt to dark room.
3. Ask students to observe the sparks of light generated when their partner bites on the candy. This is another source of an eerie light. It is called triboluminescence. This can also be demonstrated by squeezing the Lifesaver with a pair of pliers.

Demonstration VI. Fluorescent Slime Monster

1. Using the graduated cylinder, measure 100 mL of water and pour it into a plastic cup.
2. Add a very small amount (0.01 g) of fluorescein dye to the water and stir with the wooden splint.
3. Weigh out 0.5 g of guar gum and add it to the cup. Stir until dissolved. The solution will thicken slightly in one to two minutes.
4. Using a graduated cylinder, measure out 5 mL of the 4% sodium borate solution. Add the sodium borate solution to the cup and stir. The mixture should gel in one to two minutes. Best results are obtained by making measurements as precisely as possible.
5. Shine the black light on the fluorescent slime.
6. The fluorescent slime may be stored in an airtight container (like a zipper-lock bag) to keep it from drying out.

Demonstration VII. Silly Putty–Type Slime

1. Fill a paper cup with about one-half inch of white glue. This should be about 25 mL. (Using a graduated cylinder to measure out the glue is not recommended due to the cleanup involved.)
2. Using a graduated cylinder, measure out 20 mL of water and add it to the cup of glue. Stir well. Add 1–5 drops of food coloring, if desired, and stir well.
3. Using a graduated cylinder, measure out 5 mL of sodium borate solution; add it to the glue mixture and stir well.
4. Remove the solid material from the cup and place it on a piece of plastic wrap.
5. Pull the solid off the stirring rod and let the material sit for a minute or two to firm up.
6. Store the Silly Putty–type materials in a zipper-lock bag.

Teacher Tips

• In the Ghosts and Goblins demonstration, wrap the bottle with aluminum foil to make it look like a magic bottle and hide the contents.
• The one-hole stopper will prevent overpressure if the magnesium dioxide sack falls before the stopper is removed.
• For a fun alternative to the Amorphous Monster demonstration, place about 35 mL each of Part A and Part B in a paper cup, mix, and then pour the mixture into a clear plastic glove. Make sure some of the mixture is in each finger of the glove. Now watch the foam expand and fill the glove. When completely hardened, the glove can be removed, if desired, by peeling and cutting the glove away from the form. You will have made a “hand” out of polyurethane foam. The liquid may also be placed in plastic molds.
• Acetone may be used to remove small amounts of foam from the lab table.
• Do not touch the foam. It will take about 15 minutes for the surface to firmly set and may contain unreacted material for up to 24 hours. Some people will have allergic reactions to the unreacted monomers.
• Note that the cup gets warm due to the exothermic reaction.
• Do not carry out this demonstration in a glass beaker or other glassware. The foam will be almost impossible to remove from the glass.
• In the Oozing Pumpkin Head demostration,the foam will erupt almost immediately, so quickly cover the opening. The cover should be either held down or heavy enough by itself to prevent the foam from erupting out of the top.
• You may want to do this demonstration in a large demonstration tray since there is a lot of foam produced. Cleanup, however, is easy due to the presence of extremely safe final products and the generous amount of detergent.
• The beaker will get hot, so let it cool before handling.
• The slight brown tinge of the foam at the beginning is due to free iodine produced by the extreme oxidizing ability of the 30% hydrogen peroxide.
• Another catalyst that will catalyze this reaction is manganese(IV) oxide, MnO₂.
• The square can be colored orange to match the pumpkin’s color.
• Place a glowing splint in the foam and it will relight, showing the presence of oxygen.
• A dropcloth may be necessary to prevent the foam from landing on carpeting or floors. The iodine may stain the material.
• Make sure, in the Eerie Lights demostration, you stir the energetic light solution while you are adding the 0.6% potassium ferricyanide solution. This will add to the longevity of the chemiluminescence.
• Chemiluminescence is not a bright light; it is more of a glow. The darker the room, the brighter the glow will appear.
• In the Silly Putty–Type Slime demostration, if putty is too wet, stir in a little more sodium borate solution.

Discussion

Demonstration I. Ghosts and Goblins
Hydrogen peroxide decomposes to produce steam and oxygen gas. The manganese dioxide acts as a catalyst and therefore is not consumed in the reaction. The reaction is exothermic, evolving a large amount of heat.

Demonstration II. Amorphous Monster
This lightweight, polyurethane foam expands to about 30 times its original liquid volume and will become rigid in about five minutes. This rigid foam is used in furniture, packaging, insulation, flotation devices, and many other items.

Part A is a viscous cream-colored liquid containing a polyether polyol, a silicone surfactant, and a catalyst. The polyether polyol may be a substance such as polypropylene glycol [HO(C₃H₆O)_nH]. The hydroxyl (–OH) end of the polymer is the reactive site. 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 diphenylmethane diiso¬cyanate [(C₆H₅)₂C(NCO)₂] 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 2). 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 a high degree of cross-linking in the polymer, causing it to become rigid within minutes (see Equation 3). Demonstration III. Oozing Pumpkin Head
This demonstration evolves a good deal of heat as shown by the steam coming off of the foam as it is produced. The reaction, therefore, is exothermic. The action of a catalyst is demonstrated. The catalyst is the I^–(aq) ion 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 to foam. Demonstration IV. Eerie Lights
Chemical luminescence, or chemiluminescence, is a process by which chemical energy is converted directly into light energy. The chemical reaction produces an intermediate product, containing electrons in an excited state. When the electrons fall from that excited state to the more stable ground state, energy is released in the form of light.

The luminescent molecule follows an energy diagram like this: The oxidation of luminol is the best-known example of chemiluminescence. The following equation represents the reaction: For luminol to luminesce, an oxidizing agent, an alkaline pH, and some type of catalyst (such as an iron compound) are required. In this procedure, luminol(I), in the presence of hydroxide ions and a catalyst, is oxidized by hyrogen peroxide to an aminophthalte ion with electrons in an excited state(II). The chemiluminescence, or generation of light, actually occurs as the product (species II) changes from an activated state (electrons not occupying their lowest energy orbital) to its ground state (species III). The excited electrons release energy in the form of light, hυ, as they return to their ground state.

Demonstration V. More Eerie Lights
In triboluminescence, the energy needed to cause luminescence of a substance is supplied by friction (mechanical energy), rather than by a chemical reaction, as in chemiluminescence.

Wint-O-Green Lifesavers^® exhibit a brighter display of triboluminescence than other substances. Triboluminescence resembles lightning on a small scale. The friction causes an electrical charge separation in the sugar crystal. When the build-up of electrons is large enough, like lightning, the electrons jump through the air, colliding with nitrogen. The nitrogen molecules are excited and emit light as they relax back to their ground state.

Most of the energy released is ultraviolet light. Only a small fraction is in the visible region.

Wint-O-Green Lifesavers contain oil of wintergreen (methyl salicylate). This compound absorbs the ultraviolet light given off by the excited state nitrogen molecules and releases visible light as it relaxes to its ground state.

Overall: Demonstration VI. Fluorescent Slime Monster
Guar gum, a natural polymer with a molecular weight of about 220,000 g/mole, is made from the ground endosperms of Cyamopsis tetragonolobus, a legume cultivated in India as livestock feed. Guar gum has 5–8 times the thickening power of starch and is commonly used as a binding or thickening agent in foods and cosmetics.

Guar gum is a long-chain polyalcohol with 1,2-diol groupings capable of complexation with the borate ion, B(OH)₄^–. The structures given below are oversimplified, but may help to visualize the network complex as it extends in three dimensions. In addition to forming complexes with the borate ion, the interaction of long-chain polyalcohols, such as guar gum, with the borate ion leads to cross-linking of different polymer chains, or sometimes part of the same chain, in such a way that a three-dimensional network of connected chains is formed. When the concentration of cross-linked chains is high, solvent is immobilized within the network and a semisolid gel results. Because the borate ion can bond with four alcohol groups it is particularly effective in creating three-dimensional gel networks from gums such as guar gum. Other examples of networks and gels are rubber cement, gelatin, fruit jellies, agar and yogurt. Fluorescence is due to an atom or molecule emitting visible light when one of its electrons passes from a higher to a lower energy level. In this demonstration, fluorescein absorbs light in the ultraviolet and violet range of the electromagnetic spectrum and emits light of longer wavelengths. Fluorescein emits intense greenish-yellow light by fluorescence, while it appears reddish-orange by transmitted light.

Fluorescein fluoresces in the green region of the spectrum. In other words, the blue-violet end of the visible spectrum (and ultraviolet light) is converted to green so green is seen on the light incident side. The bromphenol blue absorbs all visible colors except red so that only red light is allowed to pass through the slime.

Demonstration VII. Silly Putty–Type Slime
White glue consists of a polyvinyl acetate polymer dissolved in water. Adding borate ion cross-links these chains and produces the silly putty–type properties of bouncing, stretching, shearing, and picking up newspaper print. Like its reaction with guar gum, the borate ion cross-linking forms a three dimensional network of connected polyvinyl acetate chains. The amount of cross-linking determines the properties of the putty.

References

Special thanks to Diane Burnett, Outreach Coordinator, Department of Chemistry, Purdue University, West Lafayette, Indiana, who supplied us with the instruction for this kit.

Alper, Joseph “Polymers,” ChemMatters, 1986, 4, 4 and 4, 15.

Casassa, E. Z., Sarquis, A. M. and Van Dyke, C. H. J. Chem Ed. 1986, 63, 57.

Masterton, Slowinski and Walford. Chemistry; Holt, Reinhard and Winston, New York 1980. pp. 409–416.

Shakhashiri, Bassam Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry, Vol. 1, University of Wisconsin Press, Madison 1983. p. 216.

Stenmark, Allan, Presentation at the Dryfus Mini-Institute, Chicago, Illinois.

Sweeting, L., ChemMatters, 1990, 8, pp 10–12.