No outreach chemical demonstration presentation is complete without pyrotechnics or an explosion. Demonstrations of such usually require a supply of gas (hydrogen or methane), are dangerous (sodium), or can get out of control (we recall a thermite reaction that went out of control in 1990 during a public demonstration show at the University of Illinois).
Our philosophy is to keep demonstrations as simple as possible. Rather than carrying tanks of gas, we use calcium carbide to generate acetylene gas. It is the source of our pyrotechics and explosion demonstrations. One of us (OSR) recalls when his father (a former high school chemistry teacher himself) purchased calcium carbide from an Army-Navy surplus store (believe it or not, they are still around, but in a different form). He spit on the sidewalk and added some calcium carbide to it then lit it. Professors don’t spit, so we get the same effect by adding some calcium carbide to water in a beaker. The ignition produces a flare that gets the attention of the audience. We then indicate that we can do better and proceed to the explosion.
The explosion apparatus is a plastic bottle (e.g. a taped shampoo bottle) with a hole about 4 cm from the bottom. About 0.3 – 0.4 gram of calcium carbide is added to 10 mL of water in the bottle. Acetylene has wide explosion limits; thus, calcium carbide needs only an approximate measurement. A Styrofoam cup is placed on top. After about 20 seconds, the gas mixture is ignited at the hole with a long butane grill lighter. The ensuing explosion and cup shattering is as loud and visually exciting as a hydrogen-air balloon or similar explosion.
The reaction of the audience is astounding. We do these demonstrations at the beginning of our presentation. Needless to say, we have their attention for the remaining of the program. And, we do it with an empty shampoo bottle and some calcium carbide. Can’t get any simpler than that!
We purchase the calcium carbide from The Conestoga Company sold as Bangsite. It comes in 1.75 oz tubes. This product is in granular form, and the particle size is perfect for this demonstration. The information is below:
As stated above, the explosion is loud. Thus, it is imperative to warn the audience of the impending explosion so they may cover their ears. We even suggest that parents of young children (3 years or under) to temporarily step out of the room until after the demonstration. We wear protective ear inserts. We also follow the American Chemical Society Division of Chemical Education safety guidelines and place an explosion shield in front of the apparatus. Detailed guidelines can be obtained from the website:
Watch this demonstration and let us know what you think: