Vesuvian Volcano Demo

The Ammonium Dichromate self decomposition demonstration, commonly called the “Vesuvian volcano”, is a classic High School chemistry example of how chemicals can undergo spectacular expansion during decomposition. PowerLabs brings you this classic for amusement purposes.
Ammonium Dichromate, like many other Chromium products, is a known carcinogen. Its uses include the production of pure Nitrogen gas in the laboratory, Pyrotechnics, Lithography, photo engraving, catalysts, porcelains, pigments, magnetic recording materials, amongst others. PowerLabs discourages any work involving carcinogens.

A small sample of Ammonium Dichromate is placed on top of an hourglass. The bright orange colored crystals can be seen on the photo to the left. The hourglass containing Ammonium Dichromate is placed inside a beaker with a small length of magnesium ribbon on top, so that it can be lit.

The Ammonium Dichromate decomposition becomes self sustaining at 225C, and the product combusts quietly with the evolution of some sparks and Cromium Trioxide (Cr₂O₃), a greenish powder which is lifted up in part by the rising hot Nitrogen gas. Within a short time the entire Dichromate sample has decomposed and a volume of Cr₂O₃ many times larger than the original sample volume is left behind. The Chromium Trioxide can be employed on a Thermite reaction with Aluminum or Magnesium powder.

 It is important to mention that the combustion of Cromium Trioxide is self sustained, as the molecule provides its own oxygen. This implies that this product can explode if combusted in a confined space.

Click here to watch the video 1.96MB, .MPG, 49seconds .