Note:  Contact The Fire Systems Group at Michael.Mari@colorado.edu and John.Humphrey@colorado.edu (email both) ahead of time to have the smoke alarms disabled during the class period when thermite will be performed.

Introduction

Magnesium ribbon is burned in the presence of oxygen and in a CO2 atmosphere.

2Mg(s) + O2(g)  → 2MgO(s)

2Mg(s) + CO2(g)  →  2MgO(s) + C(s) 

Prior to Lecture  (prep time ~ 20 - 30 min.)

Note: Arrange with the Fire Systems group (2-1162) to turn off smoke detectors in the area where the demo will be performed for the duration of the presentation.

Assemble the following:

  • 50 mls (= ~27.5 gm) Mg turnings in 150 ml beaker, sealed with parafilm and kept away from the dry ice until the performance of the demo.
  •  Heat-resistant mat on top of plastic tub which is inverted on wire-rack cart.
  •  goggles
  •  heat resistant gloves
  •  propane torch
  • crucible tongs
  •  fire extinguisher

Prepare the following:

Prior to the demo, obtain two intact blocks of dry ice which fit together with no air leaks.  Using a hammer and chisel, fashion a well large enough to hold the magnesium turnings in the one which will be on the bottom.  If desired, a hollow may be extended into the “roof” block also.  Return the blocks of ice to the dry ice freezer to be kept frozen until show time.  Include a sign: “Gen Chem”.

To Conduct Demonstration 

Caution: Do not look directly at the burning magnesium!

  1. Prop open exit door in Chem 140.
  2. On a wire cart, invert a large square plastic container and place the heat resistant mat on top.  Place the hollowed out piece of dry ice on top of the heat resistant mat. Place magnesiumturnings into the hollow of the bottom slab of dry ice immediately before lighting.  Ignite with the propane torch.  Keep the flame in contact with the magnesium until the metal is white hot.
  3. Place the second block of dry ice on top of the burning magnesium.
  4. Turn off the lights.  The dry ice blocks will begin to glow and spark.
  5. After magnesium is completely consumed, show black specks (carbon) and white powder (MgO) produced.

 Demo Time: ~5 - 10 minutes

Safety and Disposal

Light given off by burning magnesium is very bright and should not be viewed directly.  The magnesium in dry ice can spew burning magnesium in any direction and should not be performed in a carpeted room.  A safety shield should be placed between the dry ice and the audience or position the cart well back from the front row.

The ash can be disposed in the waste can (not the paper trash) when cool.  If the dry ice can be cleaned up, it can be returned to the dry ice freezer for someone else to use.