Sharing chemistry with the community: “The Exploding Gummy Bear”

Please read the paragraph on safety at the end before performing this experiment.

Most everyone, young and old, enjoys consuming gummy bears. They are chewy, juicy and sugary sweet! And speaking of sugar, each and every gummy bear is packed full of energy. Just how much can be qualitatively demonstrated by “The Exploding Gummy Bear” as titled by Sonia, or more accurately by “The Rapid Oxidation of Sugar.”

The demonstration is easy to perform, uses readily available materials and is a definite crowd pleaser. A gummy bear is dropped into an ignition tube containing a small amount of molten potassium or sodium chlorate. The gummy bear is rapidly consumed in a ball of fire liberating a lot of smoke in the process. Because of the large amount of smoke and other hazards, the demonstration should be performed only in a fume hood or outdoors.

While the demonstration itself is simple to perform, the underlying chemistry is not so clear-cut. The potassium chlorate is first melted, an endothermic process.

KClO₃(s) + energy → K⁺ClO₃^-(l)

The molten potassium chlorate decomposes liberating oxygen, also an endothermic process.

2K+ClO₃^- + energy → 2KCl + 3O₂(g)

This process actually takes place in two steps: 1) the formation of potassium perchlorate, followed by 2) the decomposition of the potassium perchlorate.

4KClO₃ → KCl + 3KClO₄

KClO₄ → KCl + 2O₂

The sugar present in the gummy bear undergoes rapid oxidation forming carbon dioxide and water, assuming complete combustion, a very exothermic process.

C₁₂H₂₂O₁₁(s) + 12O₂(g) → 12CO₂(g) + 11H₂O(g) + energy

Once the tube has cooled, the contents can be examined. The black material is un-reacted carbon; the white solid is potassium chloride; and the caramel-colored substance is partially decomposed sugar.

“The Exploding Gummy Bear”

Concepts

• Physical and chemical changes
• Combustion reactions
• Oxidation-reduction reactions
• Endothermic and exothermic processes
• Enthalpy: energy stored in the gummy bear candy (sugar)

Materials

• One 25 x 200 mm ignition tube
• Ring stand and clamp to mount ignition tube
• ~ 1-2 g of either potassium chlorate or sodium chlorate
• Propane torch. Bernzomatic manufactures two models:
  • TS3000KC is a self-igniting torch kit, $24.97 at Home Depot
  • UL100 is a basic kit that requires a lighter to ignite the propane $12.97; propane cylinders $3.25
• Gummy Bear candy
• Crucible tongs

Safety

• Wear safety glasses/goggles
• Wear protective gloves when transferring the chlorate salt to the ignition tube;
• Chlorates are strong oxidizing agents; keep organic substances away; never grind (especially when mixing with something like sugar).
• This demonstration should be performed only outdoors or in a fume hood with the sash pulled down. A significant amount of smoke is produced, which potentially can set off smoke alarms; as well, the smoke should not be inhaled.
• Use only ignition tubes for this demonstration; standard test tubes, even Pyrex^®, can melt, crack, or break due to excessive heat, releasing the contents.
• Carefully inspect the ignition tube for cracks, stars, or other flaws; the tube should be clean and dry; do not use if the tube is damaged in any way. It is recommended to use only new ignition tubes.
• The ignition tube should be mounted at a slight angle (~15o) with the vertical; do not mount the tube in a vertical position; gases trapped by the gummy bear will propel it out of the tube into the air. Do not use a candy that could plug up the tube and prevent the gas product from escaping.
• Even at an angle, the burning gummy bear may be propelled out of the tube; consider the possible trajectory; aim tube in a safe direction away from all people and flammable materials.

Advance preparation

• If desired, place the potassium chlorate in the ignition tube and cover with a stopper. Mount the assembly to the ring stand. Be sure to remove the stopper before heating.

Procedure

1. Fill the rounded end of an ignition tube with either potassium chlorate or sodium chlorate; if desired, you can perform the demonstration twice, once with potassium chlorate and again with sodium chlorate.
2. Mount the ignition tube with the chlorate to the ring stand at a slight angle with the vertical; be sure to attach the clamp at the mouth (top of the neck) of the ignition tube. The clamp could act as a heat sink if clamped in the middle.
3. Melt the chlorate using the portable propane torch; do not hold the flame in one place; move it around the entire bottom of the ignition tube; stop heating as soon as it is melted (sodium chlorate melts at a lower temperature than does potassium chlorate); turn off the propane torch.
4. Using the tongs to hold the gummy bear at arm’s length, drop the gummy bear into the ignition tube containing the melted chlorate salt and then stand back.

Disposal

Once the ignition tube is cool to the touch, fill it completely with water and allow it to stand overnight. The tube can then be cleaned. Solid carbon remaining in the tube can be placed in the trash.

Sonia Xu performed this demonstration for her in-class presentation — a requirement of Chemistry Outreach Service Learning  (COSL) Course — as well as part of our annual Science under the Stars. The following are Sonia’s thoughts about learning and performing the demonstration.

Part of the course requirements for the COSL is to select, plan, practice and perform a demonstration. The procedure for the gummy bear demo was easy to follow. When I observed — after just a few short steps — the colorful dazzle of light, sound and smoke, I knew I wanted to perform this demonstration.

It was decided during practice that we would use both potassium chlorate and sodium chlorate — respectively producing purple and yellow-colored flames. Dressed in spiffy blue chemistry outreach lab coats and safety goggles, we presented outside to a big semi-circle of more than three hundred excited kids and parents. The excitement was infectious yet intimidating. The oohs, ahhs and applause that arose from the audience as the purple and yellow light, hissing sound, and smoky residue spewed from the tubes left us with big smiles. It was all so fast and exciting; my heart was racing. One of the kids was jumping up and down screaming “I LOVE SCIENCE” and told me all the science he knew and what he had learned. To see a youngster so inspired and excited about science was my crowning moment of the night.

I learned numerous lessons from this experience. First and foremost is to fully understand the chemical concepts. While I had created a poster display depicting the chemical equations, in the end I struggled with what the equations were communicating. Second, stick to the plan and keep it simple. Using the two different chlorates interfered with my goal of the audience understanding the processes. Third, do not rush when speaking. These are common mistakes when first presenting science demonstrations.

All that being said, it was a great learning experience, and I am confident that my future presentations will be much improved as a result. This demo continues to be one of my favorites and I look forward to the next opportunity to perform it at an outreach event.

Editors’ note:

We are always hesitant before publishing anything on the “screaming gummy bear” demo. This demonstration has made the news several times due to injuries from classroom incidents. It is speculated that the different kind of candy, gummy bears plugging the tube, the amount of KClO₃ used, and cracked tubes contributed to the tube glass exploding. Truthfully it is tempting not to promote this demo by publishing it. But with so many teachers still doing it, as well as numerous YouTube videos providing evidence of the lack of safety precautions, it would be a missed chance not to stress the safety needed. In April 2010 we asked teachers and some members from the Lab Safety Institute for their thoughts and experiences with this demonstration. We recommend you read this in addition to following all the safety precautions listed with this demo. We have posted this again on our website — under Supplemental Materials.

Serendipitously, Michael Jansen (see his article on page 4) suggested some follow-up activities for this demo around the same time we received this article. Michael suggested tests for white-ish powdered product, which can be found inside the tube, near the top. Potassium in the product can be verified with a flame test. Silver nitrate can be added to this product after it is dissolved in distilled water. A precipitate of AgCl can be observed. This demonstrates that the product is KCl.]

*Sonia Xu is at Duke University majoring in neuroscience with a minor in chemistry. She is considering a career in medicine upon graduation.

**Dr. Kenneth Lyle, a lecturing-fellow at Duke University, serves as the instructor of the Chemistry Outreach Service Learning Course.

The Powell Family Trust, the Duke-Durham Neighborhood Partnership, and Biogen Idec – Research Triangle Park, fund the Duke Chemistry Outreach Program.