Oxidation of carbohydrates using chlorate salts — Aka: Exploding, screaming or destruction of “gummy bears”
I submitted a manuscript about the “Exploding Gummy Bear” that was published in the February issue of Chem 13 News. The editor, Jean Hein, her staff and I wrestled with the safety issues and the underlying chemistry associated with this demonstration. It was even suggested not to publish the article because of these concerns. However, after we reviewed the chemistry and expressed the detailed precautions, the article was published. The demonstration is one that will easily engage any audience no matter the age or background and seems to have become commonplace at outreach events. In the April issue of Chem 13 News, pages 2-3, two letters to the editor made comments about the logistics of the venue where the demonstration might be performed, the mechanics, reactions, safety issues and the underlying chemistry associated with the reaction. I appreciate these comments and would like to respond, as well as take the opportunity to address overall outreach demonstrations in general.
Know the logistics of the venue
The demonstrations or hands-on activities that can be performed are highly dependent on the logistics of the venue. Is it at a community outreach event, at one’s own institution as part of the chemistry instructional program, or at an on-campus outreach event? Whenever possible, I visit the venue beforehand and meet with the community partner. I use this opportunity to determine what can and cannot be performed. One unique aspect of the Duke Chemistry Outreach Program is that presentations are tailored to the needs and desires of the community partner rather than having a “canned presentation”. Similarly, I collaborate with the chemistry professors to provide demonstrations to best fit into their instructional program.
Some questions to consider when planning a presentation include:
- Do the demonstrations require electricity, water, heat or even fire?
- Are open flames permitted?
- Is an appropriate fire extinguisher available?
- Is the room equipped with smoke alarms?
- Is natural gas available?
- Are appropriate fume hoods available?
- Is the floor carpeted?
- Is the presentation to be staged inside or outside?
- What will be the seating arrangement of the audience and how close to the presenter’s table?
- Are protective tarps needed to cover the table and the surrounding floor?
- Can the demonstration be scaled up or should it be scaled down?
Over the years, the gummy bear demonstration has been staged numerous times, both indoors and outdoors. I must mention one incident that led to the evacuation of an entire school. Two presentations were performed in a school’s art/music room, which was very large and had high ceilings. I had not noticed the smoke alarm located at the top of one wall. Having staged presentations in this same room, some involving the use of open flames, I did not bother to inspect the room again. The first presentation of the gummy bear demo went as expected. However, during the second, the smoke alarm sounded and set off alarms throughout the school. Fortunately, the principal actually thanked me because a practice evacuation was required to be carried out that month. Phew! I share this to illustrate the importance of inspecting the venue in advance, even if it is the same venue, and especially if there is a different set of demonstrations.
I recommend that the gummy bear demonstration be carried out outside with the audience a good distance away, 15 feet or more. If inside, the demonstration should be performed in an appropriate fume hood in which the window can be closed. Use a small amount of chlorate salt, 1-2 g, and only the small gummy bears to limit the amount of smoke produced. Use a large ignition tube mounted on a ring stand. Be sure there are no smoke detectors in the room where you will perform the demonstration. Also be sure an ABC fire extinguisher is on hand.
Know the mechanics of the demonstration, the reaction(s), and safety issues
In front of an audience one should never, ever perform a demonstration unless one has performed first in practice — and not just practiced once, but many, many times. It is through practice that one learns the setup and mechanics of doing the demonstration. When one actually practices the demonstration, one knows what to expect. Subtle nuances not expressed in the written procedures can be identified. Safe practices can be assessed and potential hazards may become obvious. One has the opportunity to reduce these risks and make a plan to deal with them. The “talk” to be given to the intended audience can also be developed during practice. This includes what the presenter will say to the audience and at what point in the presentation he/she will do so. Similarly, the presenter should consider what questions to ask of the audience. The presenter also needs to consider what questions the audience may ask and have the answers ready. Repetitive practice helps build skills and confidence as a presenter. My outreach students find that developing the “talk” is the hardest part of the presentation, as it should be.
The setup of the gummy bear demonstration is easy, requiring very little time. I will address several concerns that were raised about the setup in the April 2014 issue.
Would 1 to 2 g [of chlorate salt] last long enough to have the students whooping?
From my experience, 1 – 2 grams (enough to fill the rounded portion of the ignition tube) is enough to not only raise the level of student engagement but also has them asking to see it again (and again). I prepare, in advance, several large ignition tubes with the chlorate salts, cover the tubes with rubber stoppers and mount the tubes on ring stands. I know the audience will want to see this demonstration again and this advanced preparation allows me to be able to fulfill these requests. Also, the small amount of chlorate takes less time to melt and reach the decomposition temperature than a larger quantity. The use of a large ignition tube reduces the possibility of breakage and tube melting to the point where a hole forms — creating a hazard of the reacting gummy bear falling out.
The chlorate salts can be easily melted using a Bunsen burner (temperature range up to 900 oC). We use portable propane torches (1200 – 1700 oC) because the outreach presentations are performed outside. The practice sessions are usually done outside, weather permitting or inside in a fume hood. Either sodium chlorate (mp 248 oC) or potassium chlorate (mp 368 oC) can be used. In the April letters to the editor, it was suggested that wooden splints could be used in place of gummy bears. I found this modification to work well. I suggest not holding the test tube — even with a clamp — but mount it on a ring stand.
Have a deep understanding of the chemistry that underlies the demonstration
Research suggests that having a deep understanding of the chemistry (true for all subjects) enables one to better communicate at a level appropriate for the intended audience. A deep understanding also reduces the chance of passing on misconceptions.
Without looking further, one might suppose that one of the reaction steps is the decomposition of the potassium chlorate into potassium chloride and oxygen. But this is not likely the case. I have not been able to find the temperature at which the decomposition process begins to occur. However, sodium chlorate decomposes at temperatures 300 oC and higher (mp 248 oC), so it can be assumed that potassium chlorate would decompose at a temperature greater than 368 oC. Therefore, most likely the potassium chlorate first changes into potassium perchlorate and oxygen followed by the potassium perchlorate decomposing into potassium chloride and more oxygen. This process occurs at a temperature above potassium chlorate’s melting point (368 oC).
The title of a demonstration can also result in misconceptions as noted in the comments in the April issue. Does the gummy bear explode? No. Does it scream? No. What title could be used that would be engaging and not lead to a misconception?
I thank the people who took the time to express their thoughts. It stimulated a good deal of thought about the reaction and the potential ways that audiences can acquire misconceptions. This is the main reason we, as educators, need to strive for a deep understanding of the chemistry involved and continue to discuss with each other possible misconceptions and improvements.