Ammonium dichromate is commonly known as Vesuvian Fire, because of its use in demonstrations of tabletop “volcanoes”. In today’s world, it’s used in pyrotechnics, but previously, photography. In this compound, as in all chromates and dichromates, chromium is in a +6 oxidation state, commonly known as hexavalent chromium. It is a salt consisting of ammonium ions and dichromate ions. Continue reading for five mind-blowing videos.
At room temperature and pressure, the compound exists as orange, acidic crystals soluble in water and alcohol. It is formed by the action of chromic acid on ammonium hydroxide with subsequent crystallisation.
Ammonium dichromate, in the presence of Mg(HSO4)2 and wet SiO2 can act as a very efficient reagent for the oxidative coupling of thiols under solvent free conditions. The reactions produces reasonably good yields under relatively mild conditions.
The volcano demonstration involves igniting a pile of the salt, which initiates an exothermic conversion. Like the well-known explosive ammonium nitrate, it is thermodynamically unstable. Its decomposition reaction proceeds to completion once initiated, producing voluminous dark green powdered chromium(III) oxide. Not all of the ammonium dichromate decomposes in this reaction. When the green powder is brought into water a yellow/orange solution is obtained from left over ammonium dichromate.
2. Ammonium Dichromate + Pellets of Mercuric Thiocyanate
Ammonium dichromate is a strong oxidising agent and reacts, often violently, with any reducing agent. The stronger the reducing agent, the more violent the reaction.
1. Fiery Arms
It has been used in pyrotechnics and in the early days of photography as well as in lithography, as a source of pure nitrogen in the laboratory, and as a catalyst.