Reaction

When magnesium is in its metal form it will burn very easily in air. However, in order to start the reaction (the burning) the magnesium metal needs a source of energy. The flame provides a source of heat so that the magnesium metal atoms can overcome their activation energy. Activation energy is the minimum energy required in order for a chemical reaction to proceed. When the magnesium metal burns it reacts with oxygen found in the air to form Magnesium Oxide, which is a compound. A compound is a material in which atoms of different elements are bonded to one another. Oxygen and magnesium come together in a chemical reaction to form this compound. After it burns, it forms a white powder of the magnesium oxide. Magnesium gives up two electrons to oxygen atoms to form this powdery product. This is an exothermic reaction. An exothermic reaction is a term that describes a chemical reaction in which there is a net release of energy.

2 Mg (s) + O₂ (g) → 2 MgO (s) + energy

Magnesium is also capable of reducing water to the highly-flammable hydrogen gas. This in turn is ignited by the excess heat given by the reduction reaction.

Mg (s) + 2H₂O → Mg(OH)₂ (s) + H₂ (g)

Magnesium also reacts with carbon dioxide to form magnesium oxide and carbon:

Mg (s) + CO₂ → 2 MgO (s) + C (s)

Hence, carbon dioxide fire extinguishers cannot be used for extinguishing magnesium fires either. Burning magnesium is usually quenched by using a Class D dry chemical fire extinguisher, or by covering the fire with sand to remove its air source.

Materials

• strip of magnesium metal ribbon - 4 inches long
• lighter

Directions

1. Hold the piece of magnesium metal ribbon in a pair of tongs.
2. Take the lighter and hold the magnesium metal ribbon in the hottest part of the flame.
3. It will soon catch fire and emit a very bright light.
4. CAUTION DO NOT LOOK DIRECTLY AT THE BRIGHT LIGHT. Briefly gaze at the light out of the corner of your eye.

Safety

• Wear goggles.
• Do not let children do this.
• Do not look directly at the light emitted from the metal.
• Make sure you hold the metal securely with the tongs.
• Keep away from combustible materials.

As a result, water cannot extinguish magnesium fires; the hydrogen gas produced will only intensify the fire. Wear googles that filter out UV light. Throw the powder in the garbage.

Outside Links

• Driscoll, Jerry A. "Demonstration of burning magnesium and dry ice (TD)." J. Chem. Educ. 1978, 55, 450.
• Feinstein, H. I. "Ignition of magnesium in porcelain." J. Chem. Educ. 1982, 59, 159.
• Laing, Michael. "A WARNING: Explosion Hazards of Reacting Magnesium and Aluminum with Powdered Silver Nitrate (LTE)." J. Chem. Educ. 1994, 71, 270.
• Moyer, Ralph O. "Synthesis and structure of magnesium oxide or calcium oxide. An integrated inorganic-physical experiment." J. Chem. Educ. 1975, 52, 612.

References

• Shakhashiri, Bassam Z. "Chemical Demonstrations", U. Wisconsin Press, 1983,Vol. 1, p.38.

• http://www.angelo.edu/faculty/kboudr..._magnesium.htm
• http://www.newton.dep.anl.gov/askasc.../chem03362.htm

Contributors

• Charles Ophardt, Professor Emeritus, Elmhurst College; Virtual Chembook

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