Molybdenum(VI) oxide
1912884
220563356
2008-06-20T13:35:56Z
65.112.42.84
Corrected chemical formula from MO6 to MoO6
{{Chembox new
| Name = Molybdenum(VI) oxide
| ImageFile = Molybdenum(VI) oxide.jpg
<!-- | ImageSize = 200px -->
| ImageName = Molybdenum(VI) oxide
| IUPACName = Molybdenum trioxide<br />Molybdenum(VI) oxide
| OtherNames = Molybdic anhydride<br />[[Molybdite]]<br />Molybdenum oxide<br />Molybdic trioxide
| Name = Solid properties
| Name = Liquid properties
| Name = Gas properties
| Section1 = {{Chembox Identifiers
| CASNo = 1313-27-5
}}
| Section2 = {{Chembox Properties
| Formula = MoO<sub>3</sub>
| MolarMass = 143.94 g/mol
| Appearance = yellow solid
| Density = 4.7 g/cm<sup>3</sup>, solid
| Solubility = 0.5 g/L (20 °C)
| MeltingPt = 795 °C
| BoilingPt = 1155 °C
| pKa =
}}
| Section3 = {{Chembox Structure
| Coordination = distorted [[Octahedron|octahedral]]
| CrystalStruct = [[orthorhombic]]
}}
| Section4 = {{Chembox Thermochemistry
| DeltaHf = −745.17 kJ/mol
| Entropy = 77.78 J/(mol K)
| Entropy = 114.93 J/(mol K)
| Entropy = 283.89 J/(mol K)
| DeltaHf = −745.17 kJ/mol
| Entropy = 77.78 J.K<sup>–1</sup>.mol<sup>–1</sup>
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS =
| EUClass = Harmful ('''Xn''')<br />Irritant ('''Xi''')
| RPhrases = {{R36/37}}, {{R48/20/22}}
| SPhrases = {{S2}}, {{S22}}, {{S25}}
| FlashPt = not applicable
}}
| Section8 = {{Chembox Related
| OtherAnions = [[Molybdenum disulfide]]
| OtherCations = [[Chromium trioxide]]<br />[[Molybdenum dioxide]]<br />[[Tungsten trioxide]]
| OtherCpds = [[Molybdic acid]]<br />[[Sodium molybdate]]}}
}}
'''Molybdenum(VI) oxide''' is [[chemical compound]] with the [[chemical formula|formula]] [[molybdenum|Mo]]O<sub>3</sub>. This compound is produced on the largest scale of any molybdenum compound. It occurs as the rare [[mineral]] molybdite. Its chief application is as an oxidation [[catalyst]] and as a raw material for the production of molybdenum metal.
Valency of Molybdenum is +6
==Structure==
In the gas phase, three oxygen atoms are double bonded to the central molybdenum atom. In the solid state, [[anhydrous]] MoO<sub>3</sub> is composed of layers of distorted MoO<sub>6</sub> octahedra in an orthorhombic crystal. The octahedra share edges and form chains which are cross-linked by oxygen atoms to form layers. The octahedra have one short molydenum-oxygen bond to a non-bridging oxygen.<ref>Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.</ref><br />
The image shows a section of the chain made up from edge sharing distorted octahedra. The oxygen atoms above and below the chain link to other chains to build the layer.[[Image:MoO3 chains.png|200px|MoO3]]
==Preparation and principal reactions==
MoO<sub>3</sub> is produced industrially by burning [[molybdenum disulfide]], the chief ore of molybdenum:
: 2 MoS<sub>2</sub> + 7 [[oxygen|O<sub>2</sub>]] → 2 MoO<sub>3</sub> + 4 SO<sub>2</sub>
The laboratory synthesis entails the acidification of aqueous solutions of [[sodium molybdate]]:<ref>Heynes, J. B. B.; Cruywagen, J. J. "Yellow Molybdenum(VI) Oxide Dihydrate" Inorganic Syntheses, 1986, volume 24, pp. 191. ISBN 0-471-83441-6.</ref>
:Na<sub>2</sub>MoO<sub>4</sub> + H<sub>2</sub>O + 2 [[Perchloric acid|HClO<sub>4</sub>]] → MoO<sub>3</sub>(H<sub>2</sub>O)<sub>2</sub> + 2 NaClO<sub>4</sub>
The dihydrate loses water readily to give the monohydrate. Both are bright yellow in color.
Molybdenum(VI) oxide dissolves slightly in water to give "molybdic acid." In base, it dissolves to afford the molybdate anion.
==Uses==
Molybdenum(VI) oxide is used to manufacture molybdenum metal, which serves as an additive to steel and corrosion-resistant alloys. The relevant conversion entails treatment of MoO<sub>3</sub> with hydrogen at elevated temperatures:
:MoO<sub>3</sub> + 3 H<sub>2</sub> → Mo + 3 H<sub>2</sub>O
It is also a component of the [[Catalysis|co-catalyst]] used in the industrial production of [[acrylonitrile]] by the [[oxidation]] of [[propene]] and [[ammonia]].
Because of its layered structure and the ease of the Mo(VI)/Mo(V) couple, MoO<sub>3</sub> is of interest in electrochemical devices and displays.<ref>Ferreira, F. F.; Souza Cruz, T. G.; Fantini, M. C. A.; Tabacniks, M. H.; de Castro, S. C.; Morais, J.; de Siervo, A.; Landers, R.; Gorenstein, A. ''Solid State Ionics.'' '''2000''', ''136-137'', 357.</ref>
==References==
<references/>
==External links==
* {{Greenwood&Earnshaw}}
* [http://ntp.niehs.nih.gov/index.cfm?objectid=070A72C6-E9C1-AE67-4BFAB97AD0F427E8/ U.S. Department of Health and Human Services National Toxicology Program]
* [http://hse.imoa.info/Default.asp?Page=156/ International Molybdenum Association]
*[http://periodic.lanl.gov/elements/42.html/ Los Alamos National Laboratory- Molybdenum]
[[Category:Molybdenum compounds]]
[[Category:Oxides]]
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