Chromium trioxide


Chromium trioxide
Chromium trioxide
Identifiers
CAS number 1333-82-0 YesY
PubChem 14915
ChemSpider 14212 YesY
UNII 8LV49809UC YesY
UN number 1463
ChEBI CHEBI:48240 YesY
RTECS number GB6650000
Jmol-3D images Image 1
Properties
Molecular formula CrO3
Molar mass 99.99 g mol−1
Appearance dark red granular solid
Odor odorless
Density 2.70 g/cm3 (20 °C)
Melting point

197 °C, 470 K, 387 °F

Boiling point

251 °C, 524 K, 484 °F (decomposes)

Solubility in water 61.7 g/100 mL (0 °C)
63 g/100 mL (25 °C)
67 g/100 mL (100 °C)
Solubility soluble in sulfuric acid, nitric acid
Hazards
MSDS ICSC 1194
EU Index 024-001-00-0
EU classification Oxidizer (O)
Carc. Cat. 1
Muta. Cat. 2
Repr. Cat. 3
Very toxic (T+)
Dangerous for the environment (N)
R-phrases R45, R46, R9, R24/25, R26, R35, R42/43, R48/23, R62, R50/53
S-phrases S53, S45, S60, S61
NFPA 704
NFPA 704.svg
1
3
1
OX
LD50 80 mg/kg
 YesY trioxide (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Chromium trioxide is the inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name.[1] This compound is a dark-red/orange brown solid, which dissolves in water concomitant with hydrolysis. Millions of kilograms are produced annually, mainly for electroplating.[2]

Contents

Production, structure, and basic reactions

Chromium trioxide is generated by treating sodium chromate or the corresponding sodium dichromate with sulfuric acid:[1]

H2SO4 + Na2CrO4 → CrO3 + Na2SO4 + H2O

Approximately 100M kg are produced annually by this or similar routes.[2]

The solid consists of chains of tetrahedrally coordinated chromium atoms that share vertices. Each chromium center, therefore, shares two oxygen centers with neighbors. Two oxygen atoms are not shared, giving an overall stoichiometry of 1:3.[3][4]

Ball-and-stick model of chains in the crystal structure of CrO3

The structure of monomeric CrO3 has been calculated using density functional theory, and is predicted to be pyramidal (point group C3v) rather than planar (point group D3h).[5]

Ball-and-stick model of the DFT-calculated structure of the CrO3 monomer

Chromium trioxide decomposes above 197°C liberating oxygen eventually giving Cr2O3:

4 CrO3 → 2 Cr2O3 + 3 O2

It is used in organic synthesis as an oxidant, often as a solution in acetic acid,[3] or acetone in the case of the Jones oxidation. In these oxidations, the Cr(VI) converts 1.5 equivalents of alcohols to the corresponding ketones or aldehydes:

2 CrO3 + 3 RCH2OH → Cr2O3 + 3 RCHO + 3 H2O

Applications

Chromium trioxide is mainly used in chrome-plating. It is typically employed with additives that affect the plating process but do not react with the trioxide. The trioxide reacts with cadmium, zinc, and other metals to generate passivating chromate films that resist corrosion. It is also used in the production of synthetic rubies.

Safety

Chromium trioxide ignition of ethanol

Chromium trioxide is highly toxic, corrosive, and carcinogenic.[6] It is the main example of hexavalent chromium, an environmental hazard. The related chromium(III) derivatives are not particularly dangerous; thus, reductants are used to destroy chromium(VI) samples.

Chromium trioxide, being a powerful oxidizer, will ignite some organic materials (such as ethanol) on contact.

References

  1. ^ a b "Chromium Trioxide". Chemicalland21. http://www.chemicalland21.com/industrialchem/inorganic/CHROMIUM%20TRIOXIDE.htm. 
  2. ^ a b Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinge. Chromium Compounds. in Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH, 2002. doi:10.1002/14356007.a07_067
  3. ^ a b Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN 0-471-19957-5 
  4. ^ Stephens, J. S.; Cruickshank, D. W. J. (1970). "The crystal structure of (CrO3)". Acta Cryst. B 26: 222–226. doi:10.1107/S0567740870002182. 
  5. ^ Zhai, Hua-Jin; Li, Shenggang; Dixon, David A.; Wang, Lai-Sheng (2008). "Probing the Electronic and Structural Properties of Chromium Oxide Clusters (CrO3)n and (CrO3)n (n = 1–5): Photoelectron Spectroscopy and Density Functional Calculations". J. Am. Chem. Soc. 130 (15): 5167–5177. doi:10.1021/ja077984d. 
  6. ^ "Chromium Trioxide (MSDS)". J. T. Baker. http://hazard.com/msds/mf/baker/baker/files/c4400.htm. Retrieved 2007-09-13. 

External links


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Look at other dictionaries:

  • chromium trioxide — chromo(VI) oksidas statusas T sritis chemija formulė CrO₃ atitikmenys: angl. chromic anhydrite; chromium trioxide; chromium(VI) oxide rus. хрома трехокись; хрома(VI) оксид; хромовой ангидрид ryšiai: sinonimas – chromo trioksidas …   Chemijos terminų aiškinamasis žodynas

  • chromium trioxide — see chromic acid …   Medical dictionary

  • chromium trioxide — noun : chromic anhydride …   Useful english dictionary

  • Chromium(IV) oxide — Chromium(IV) oxide[1] IUPAC name …   Wikipedia

  • Chromium(III) oxide — Chromium(III) oxide …   Wikipedia

  • Chromium oxide — may refer to: Chromium(II) oxide, CrO Chromium(III) oxide, Cr2O3 Chromium dioxide (chromium(IV) oxide), CrO2 Chromium trioxide (chromium(VI) oxide), CrO3 Chromium(VI) oxide peroxide, CrO5 Mixed valence species, such as Cr8O21 …   Wikipedia

  • chromium — /kroh mee euhm/, n. 1. a lustrous, hard, brittle, metallic element used in alloy steels for hardness and corrosion resistance, as in stainless steel, and for plating other metals: chromium salts are used as pigments and mordants. Symbol: Cr; at.… …   Universalium

  • Chromium — This article is about the chemical element. For other uses, see Chromium (disambiguation). vanadium ← chromium → manganese ↑ Cr ↓ Mo …   Wikipedia

  • chromium(VI) oxide — chromo(VI) oksidas statusas T sritis chemija formulė CrO₃ atitikmenys: angl. chromic anhydrite; chromium trioxide; chromium(VI) oxide rus. хрома трехокись; хрома(VI) оксид; хромовой ангидрид ryšiai: sinonimas – chromo trioksidas …   Chemijos terminų aiškinamasis žodynas

  • chromium — A metallic element, atomic no. 24, atomic wt. 51.9961. A dietary essential bioelement. 51Cr (half life of 27.70 days) is used as a diagnostic aid in many disorders ( e.g., gastrointestinal protein …   Medical dictionary


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