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_oxide.jpg) | |
| Names | |
|---|---|
| IUPAC name Chromium trioxide | |
| Other names Chromic anhydride, Chromium(VI) oxide, Chromic acid (misnomer) | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChemSpider |
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| ECHA InfoCard | 100.014.189 |
| RTECS number |
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| UNII | |
| UN number | 1463 |
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| Properties | |
| CrO3 | |
| Molar mass | 99.993 g·mol−1 |
| Appearance | Dark red granular solid,deliquescent |
| Odor | Odorless |
| Density | 2.7 g/cm3 (20 °C)[1] |
| Melting point | 197 °C (387 °F; 470 K)[1] |
| Boiling point | 250 °C (482 °F; 523 K) decomposes[1] |
| Solubility | Soluble inH2SO4,HNO3,(CH3CH2)2O,CH3COOH,(CH3)2CO |
| +40·10−6 cm3/mol[1] | |
| Thermochemistry | |
Std molar entropy(S⦵298) | 73.2 J/(mol·K)[3] |
Std enthalpy of formation(ΔfH⦵298) | −589.3 kJ/mol[4] |
| Hazards | |
| GHS labelling: | |
     [5] | |
| Danger | |
| H271,H301+H311,H314,H317,H330,H334,H335,H340,H350,H361f,H372,H410[5] | |
| P210,P260,P280,P303+P361+P353,P304+P340+P310,P305+P351+P338[5] | |
| NFPA 704 (fire diamond) | |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 80 mg/kg (rats, oral)[6] |
| Safety data sheet (SDS) | ICSC 1194 |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Chromium trioxide (also known aschromium(VI) oxide orchromic anhydride) is aninorganic compound with theformulaCrO3. It is theacidic anhydride ofchromic acid, and is sometimes marketed under the same name.[6]This compound is a dark-purplesolid under anhydrous conditions and bright orange when wet. The substance dissolves in water accompanied by hydrolysis.[clarification needed] Millions of kilograms are produced annually, mainly forelectroplating.[7] Chromium trioxide is a powerful oxidiser, amutagen, and acarcinogen.[8]
Chromium trioxide is generated by treatingsodium dichromate withsulfuric acid:[6]
Approximately 100,000 tonnes are produced annually by this or similar routes.[7]
The solid consists of chains of tetrahedrally coordinated chromium atoms that share vertices. Eachchromium center therefore shares two oxygen centers with neighbors. Two oxygen atoms are not shared, giving an overall stoichiometry of 1:3.[9][10]
The structure of monomericCrO3 has been calculated usingdensity functional theory, and is predicted to bepyramidal (point group C3v) rather thanplanar (point group D3h).[11]
Chromium trioxide decomposes above 197 °C, liberating oxygen and eventually givingCr2O3:
It is used inorganic synthesis as an oxidant, often as a solution inacetic acid,[9] oracetone in the case of theJones oxidation. In these oxidations, the Cr(VI) convertsprimary alcohols to the correspondingcarboxylic acids andsecondary alcohols toketones. The reactions are shown below:
Chromium trioxide is mainly used inchrome plating. It is typically employed with additives that affect the plating process but do not react with the trioxide. The trioxide reacts withcadmium,zinc, and other metals to generate passivating chromate films that resistcorrosion. It is also used in the production ofsynthetic rubies. Chromic acid solution is also used in applying types ofanodic coating toaluminium, which are primarily used in aerospace applications. On the International Space Station, it is used to control bacteria growth in the wastewater storage tank. A chromic acid/phosphoric acid solution is also the preferredstripping agent of anodic coatings of all types.
Chromium trioxide is highly toxic, corrosive, and carcinogenic.[12] It is the main example ofhexavalent chromium, anenvironmental hazard.[13] 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 organic materials such asalcoholson contact.
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