Ammonium bichromate

Ammonium dichromate

Names
IUPAC name Ammonium dichromate
Other names Ammonium bichromate Ammonium pyrochromate
Identifiers
CAS Number	7789-09-5 Y
3D model (JSmol)	Interactive image
ChemSpider	23002 Y
ECHA InfoCard	100.029.221
PubChem CID	24600
RTECS number	HX7650000
UNII	5J18BP595G N
UN number	1439
InChI InChI=1S/2Cr.2H3N.7O/h;;2*1H3;;;;;;;/q;;;;;;;;;2*-1/p+2 Y Key: JOSWYUNQBRPBDN-UHFFFAOYSA-P Y InChI=1/2Cr.2H3N.7O/h;;2*1H3;;;;;;;/q;;;;;;;;;2*-1/p+2/rCr2O7.2H3N/c3-1(4,5)9-2(6,7)8;;/h;2*1H3/q-2;;/p+2 Key: JOSWYUNQBRPBDN-RFRSXZKWAS
SMILES [O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O.[NH4+].[NH4+]
Properties
Chemical formula	(NH4)2Cr2O7
Molar mass	252.07 g/mol
Appearance	Orange-red crystals
Density	2.115 g/cm3
Melting point	180 °C (356 °F; 453 K) decomposes
Solubility in water	18.2 g/100ml (0 °C) 35.6 g/100ml (20 °C) 40 g/100ml (25 °C) 156 g/100ml (100 °C)
Solubility	insoluble in acetone soluble in alcohol
Hazards
Safety data sheet	ICSC 1368
GHS pictograms
GHS hazard statements	H272, H301, H312, H314, H317, H330, H334, H340, H350, H360, H372, H410
GHS precautionary statements	P201, P220, P260, P273, P280, P284
NFPA 704	1 2 1 OX
Autoignition temperature	190 °C (374 °F; 463 K)
Related compounds
Other cations	Potassium dichromate Sodium dichromate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

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

Ammonium dichromate is sometimes known as Vesuvian Fire, because of its use in demonstrations of tabletop "volcanoes". However, this demonstration has become unpopular in schools due to the compound's carcinogenic nature. It has also been used in pyrotechnics and in the early days of photography.

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.

The (NH₄)₂Cr₂O₇ crystal (C2/c, z=4) contains a single type of ammonium ion, at sites of symmetry C₁(2,3). Each NH₄⁺ centre is surrounded irregularly by eight oxygen atoms at N—O distances ranging from ca. 2.83 to ca. 3.17 Å, typical of hydrogen bonds.

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. It is also used as a mordant for dyeing pigments, in the manufacturing of alizarin, chrome alum, leather tanning and oil purification.