|Jmol-3D images||Image 1|
|Molar mass||99.99 g mol−1|
|Appearance||dark red granular solid
|Density||2.70 g/cm3 (20 °C)|
197 °C, 470 K, 387 °F
251 °C, 524 K, 484 °F (decomposes)
|Solubility in water||61.7 g/100 mL (0 °C)
63 g/100 mL (25 °C)
67.45 g/100 mL (100 °C)
|Solubility||soluble in sulfuric acid, nitric acid, ethyl ether, acetic acid, acetone|
|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|
|Std enthalpy of
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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. This compound is a dark-purple solid under anhydrous conditions, bright orange when wet and which dissolves in water concomitant with hydrolysis. Millions of kilograms are produced annually, mainly for electroplating.
Production, structure, and basic reactions
- H2SO4 + Na2Cr2O7 → 2CrO3 + Na2SO4 + H2O
Approximately 100M kg are produced annually by this or similar routes.
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.
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, or acetone in the case of the Jones oxidation. In these oxidations, the Cr(VI) converts primary alcohols to the corresponding carboxylic acids and secondary alcohols to ketones. The reactions are given below:
- Primary alcohols
- 4 CrO3 + 3 RCH2OH + 12 H+ → 3 RCOOH + 4 Cr3+ + 9 H2O
- Secondary alcohols
- 2 CrO3 + 3 R2CHOH + 6 H+ → 3 R2C=O + 2 Cr3+ + 6 H2O
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. Chromic acid solution is also used in applying types of anodic coating to aluminum, which are primarily used in aerospace applications. A Chromic Acid/Phosphoric Acid solution is also the preferred stripping agent of anodic coatings of all types.
Chromium trioxide is highly toxic, corrosive, and carcinogenic. 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.
- "Chromium Trioxide". Chemicalland21.
- 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
- 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
- Stephens, J. S.; Cruickshank, D. W. J. (1970). "The crystal structure of (CrO3)∞". Acta Cryst. B 26 (3): 222–226. doi:10.1107/S0567740870002182.
- 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.
- "Chromium Trioxide (MSDS)". J. T. Baker. Retrieved 2007-09-13.
|Wikimedia Commons has media related to Chromium trioxide.|
- ATSDR Case Studies in Environmental Medicine: Chromium Toxicity U.S. Department of Health and Human Services
- Chromium Trioxide at The Periodic Table of Videos (University of Nottingham)