Ammonium dichromate

Chembox new
Name = Ammonium dichromate
ImageFile = (NH4)2Cr2O7.jpg
ImageName =
IUPACName = Ammonium dichromate
OtherNames = Ammonium Pyrochromate
Section1 = Chembox Identifiers
CASNo = 7789-09-5
RTECS = HX7650000
Section2 = Chembox Properties
Formula = H₈N₂Cr₂O₇
MolarMass = 252.07 g/mol
Appearance = Orange crystals
Density = 2.15 g/cm³
Solubility = 36.4 g/100 mL (20 °C)
MeltingPt = 180°C (? K)
BoilingPt = decomposes
Section3 = Chembox Structure
Coordination = see dichromate
CrystalStruct =
Section7 = Chembox Hazards
ExternalMSDS =
MainHazards = oxidizer
RPhrases = R45 R46 R60 R61 R2 R8 R21 R25 R26 R34 R42/43 R48/23 R50/53
SPhrases = S53 S45 S60 S61
Section8 = Chembox Related
OtherCations = Potassium dichromate
sodium dichromate

Ammonium dichromate is the inorganic compound with the formula (NH₄)₂Cr₂O₇. This salt is sometimes known as "Vesuvian Fire", because of its use in the formation of tabletop "volcanoes". It has been used in pyrotechnics and in the early days of photography.

The volcano demonstration involves igniting a pile of the salt, which initiates the following conversion::(NH₄)₂Cr₂O₇(s) → Cr₂O₃(s) + N₂(g) + 4H₂O(g)Like the well-known explosive ammonium nitrate, ammonium dichromate contains both an oxidizer (dichromate) and a reducer (ammonium). [G.A.P. Dalgaard, A.C. Hazell and R.G. Hazell"The Crystal Structure of Ammonium Dichromate, (NH₄)₂Cr₂O₇" Acta Chemica Scandinavica A28 (1974) 541-545] The reaction proceeds to completion once initiated. This demonstration finds only limited use because the chromium(III) oxide ash produced by this reaction is toxic, possibly carcinogenic.

References