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Vesuvius Fire Introduction
The eruption of an ammonium dichromate (NH4)2Cr2O7 volcano is a classic chemistry demonstration. The ammonium dichromate glows and emits sparks as it decomposes and produces copious amounts of green chromium (III) oxide ash. This demonstration is simple to prepare and perform. The decomposition of ammonium dichromate commences at 180°C, becoming self-sustaining at ~225°C. The oxidant (Cr6+) and the reductant (N3-) are present in the same molecule.
(NH4)2Cr2O7 → Cr2O3 + 4 H2O + N2
The procedure works well in both a lighted or darkened room.
- ~20 grams of ammonium dichromate
- sand tray or ceramic tile, for use in ventilation hood OR
- 5-liter round bottom flask and porcelain filtering funnel
- gas burner (e.g., Bunsen) OR
- butane lighter or match, for use with flammable liquid (e.g., ethanol, acetone)
If you are using a hood:
- Make a pile (volcanic cone) or ammonium dichromate on a tile or tray of sand.
- Use a gas burner to heat the tip of the pile until the reaction begins or dampen the tip of the cone with a flammable liquid and light it with a lighter or match.
If you are not using a ventilation hood:
- Pour the ammonium dichromate into a large flask.
- Cap the flask with a filtration funnel, which will prevent the majority of the chromium (III) oxide from escaping.
- Apply heat to the bottom of the flask until the reaction begins.
Chromium III and chromium VI, as well at its compounds, including ammonium dichromate, are known carcinogens. Chromium will irritate the mucous membranes. Therefore, take care to perform this demonstration in a well-ventilated area (preferably a ventilation hood) and avoid skin contact or inhalation of the materials. Wear gloves and safety goggles when handling ammonium dichromate.
B.Z. Shakhashiri, Chemical Demonstrations: A Handbook for Teachers of Chemistry, Vol. 1, University of Wisconsin Press, 1986, pp. 81-82.
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