Ammonium dichromate

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Ammonium dichromate
Names
IUPAC name
Ammonium dichromate
Other names
Ammonium bichromate
Ammonium pyrochromate
Diammonium dichromate
Vesuvian Fire
Properties
(NH4)2Cr2O7
Molar mass 252.07 g/mol
Appearance Orange crystalline solid
Odor Odorless
Density 2.115 g/cm3
Melting point 180 °C (356 °F; 453 K) (decomposition)
Boiling point Decomposes
18.2 g/100ml (0 °C)
35.6 g/100ml (20 °C)
40 g/100ml (25 °C)
156 g/100ml (100 °C)
Solubility Soluble in alcohols
Insoluble in acetone
Hazards
Safety data sheet Sigma-Aldrich
Related compounds
Related compounds
Potassium dichromate
Sodium dichromate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Ammonium dichromate is the inorganic compound with the formula (NH4)2Cr2O7.

Properties

Chemical

Ammonium dichromate decomposes when heated, releasing nitrogen, water vapors and green chromium(III) oxide particles in a manner similar to a volcanic eruption, hence why this property makes it widely used in various pyrotechnic demonstrations.

(NH4)2Cr2O7 → Cr2O3 + N2 + 4 H2O

Physical

Ammonium dichromate is a red-orange solid, soluble in water and alcohols, but less so in other solvents.

Availability

Ammonium dichromate can be bought from various chemical suppliers. It can also be found on eBay and Amazon.

Since September 2017, ammonium dichromate is banned in EU.

Preparation

Ammonium dichromate can be made by reacting sodium dichromate (which in turn can be made by the action of sodium hypochlorite aka household bleach to chromium(III) hydroxide or oxide) with ammonium chloride. Since sodium chloride is more soluble than ammonium dichromate at low temperatures, cooling the solution will cause ammonium dichromate to crystalize out of the solution.

Projects

Handling

Safety

Ammonium dichromate is flammable, oxidizer and a known carcinogen

Storage

Ammonium dichromate should be stored in closed bottles, away from acids and flame sources.

Disposal

Can be reduced to Cr(III) using aqueous solutions of ascorbic acid. Other reducing agents, such as sodium/potassium metabisulfite, sulfite, thiosulfate can be used.

Burning ammonium dichromate is not recommended, as small amounts of it will be spread in air.

References

Relevant Sciencemadness threads