Magnesium/Dry Ice
- Page ID
- 131408
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Required Training |
Required PPE |
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UC Lab Safety Fundamentals Online Cryogen Safety at UC Davis |
Flame-resistant lab coat, safety glasses/goggles, cryo-gloves (blue fabric) |
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Performers Required: 2 |
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Equipment |
Chemicals |
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Drill with 2” hole saw bit and hacksaw |
Magnesium (Mg) (1/2 inch) ribbon and turnings |
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Insulated cooler for transporting dry ice |
Solid CO2 (dry ice), 1 slabs cut in half |
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Propane torch |
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Procedure:
- Wrap a 0.5-meter length of Mg ribbon around a pencil or similarly sized object to form a tight coil. Then, wrap this coil into a spiral, such that it will fit in the well circular hole in the slab of dry ice.
- Cut the slab in half with a hacksaw. Drill a well (2” diameter) in the middle of a slab of dry ice, approximately 1/3 of the way through it. Then, with the drill turned off, use the edge of the hole saw bit to chip out the disc in the middle, leaving a circular depression. The back of a claw hammer can also be used to pry out the disc. Take care not to crack the half slab when doing this.
- Place the half slab with the hole on the ground, with the hole facing up, at least 10 feet from the audience and away from flammable materials.
- With a second performer holding the other half of the slab (no wells) of dry ice at the ready, place the coil of Mg in the circular hole, add the turnings, and use the torch to ignite it. Ensure any magnesium containers are 10 feet away before ignition. As soon as the Mg starts to burn, the second performer must quickly slide the solid slab of dry ice on top of the other, taking care not to crack either slab. The audience should be warned to look away from the lighted magnesium until the solid slab has been placed over it.
- Stand back from the demo, as sparks of burning Mg will escape between the slabs and fly up to 1 foot away.
Clean-up: Once the magnesium has completely combusted, the dry ice may be returned to its cooler. After the show, the ashes of the Mg ribbon may be discarded in the trash, and the dry ice placed in a fume hood until it completely sublimes.
Hazards: Dry ice sublimes at -78.5 °C (194.5 K), and prolonged contact with skin will cause frostbite. Never place dry ice in a closed container, as the build-up of pressure may cause the container to burst, which could injure anyone nearby. Mg is a flammable solid and burns at extremely high temperatures (>3000 °C), simultaneously producing very bright white and UV light. Hazards include thermal burns and vision damage if the combustion is viewed directly.
Principle: Initially the Mg burns in a conventional manner, using oxygen from the air. After a few seconds the light will dim, and at this point the atmospheric oxygen is being completely consumed in the burning chamber (the space between the slabs). However, Mg has such a powerful affinity for oxygen that it begins to steal oxygen from the dry ice, producing magnesium oxide (MgO) and carbon soot. The reaction then proceeds much faster and the light gets brighter, and the Mg will continue to burn until all of it has been consumed.
Notes: This demonstration is most impressive with the lights dimmed. The Mg ribbon should not be placed in the dry ice significantly before the demonstration, as this seems to diminish the intensity of the reaction. Using larger quantities of Mg ribbon also appears less important to the intensity of the reaction than properly optimizing the available surface area; a smaller piece that has been carefully coiled and wound burns just as brightly as a much larger piece crumpled into a ball. Adding magnesium turnings helps the ignition. If the solid piece of dry ice is place before the magnesium is completely lit, it will extinguish the flame. If this occurs, wait 5 minutes before assessing the state of the magnesium and attempting re-lighting. DO NOT add more magnesium in case the flame is not completely extinguished.