Brief Description:
When a piece of magnesium ribbon is ignited, light and heat are produced.
Purpose/Goal:
A quick demonstration which illustrates the concept of an exothermic reaction, as well as one that produces light energy.
Explanation of Experiment:
The oxidation or combustion of magnesium in air has long been used as a source of intense light in photography and for other photochemical reactions. The energy released in this combustion occurs as the magnesium reacts with oxygen in the air according to the equation:
2 Mg (s) + O2 (g) → 2 MgO (s)
The heat of formation of magnesium oxide is -601.83 kJ/mol. When magnesium burns, approximately 10% of the energy of combustion occurs as light, a value unapproached among known transformations of energy used in the production of light.
Materials Preparation:
- 6-8 cm magnesium ribbon sanded to remove oxide coating
- Bunsen burner, charcoal grill lighter or similar
- Tongs
Presentation:
Light the burner and adjust the flame to light blue. Holding one end of the magnesium ribbon with tongs, place the other end in the flame until it ignites. The burning ribbon should be held at arm’s length. DO NOT LOOK DIRECTLY AT THE BURNING RIBBON. The burning magnesium yields brilliant light and intense heat.
Hazards:
The burning magnesium ribbon produces light of sufficient intensity to cause temporary loss of sight. Avoid looking directly at the light source. The burning of magnesium in air produces intense heat which can cause burns and initiate combustion in flammable materials. Since a carbon dioxide fire extinguisher will not extinguish burning magnesium, a dry-powder extinguisher must be used.
Disposal:
Once cooled to room temperature, the magnesium oxide solid from the ribbon should be discarded in a waste container.
Video:
General Concept:
- Light
- Thermodynamics
Type of Reaction:
- Exothermic
- Oxidation/Reduction
Primary Reference:
- Shakhashiri, B.Z. 1983, Chemical Demonstrations – A Handbook for Teachers of Chemistry, vol. 1 pp. 38-39.
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