Molybdenum trioxide
Orthorhombic
Pbnm
- A = 392 pm
- B = 1394 pm
- C = 366 pm
- Molybdenum trioxide
- Molybdic
- Water lead Earth
Yellowish green, odorless solid
Fixed
4.70 g · cm -3
795 ° C
1155 ° C
Poorly in water ( 0.5 g · l-1 at 20 ° C)
Attention
Repealed as carcinogenic
125 mg · kg -1 ( LD50, rat, oral)
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Molybdenum ( VI) oxide is a white powdery compound which remains in the roasting many molybdenum compounds.
History
1778, Carl Wilhelm Scheele from molybdenite by treatment with nitric acid to produce molybdenum (VI ) oxide. Peter Jacob Hjelm in 1782 reduced the oxide with carbon to elemental molybdenum.
Occurrence
In nature, it occurs in the form of the rare mineral Molybdit.
Production and representation
Molybdenum ( VI) oxide is produced industrially by oxidation of the molybdenum (IV ) sulfide obtained:
In the laboratory, it may also be obtained by reaction of nitric acid and ammonium or sodium molybdate in perchloric acid, and wherein each of molybdenum ( VI) oxide dihydrate arises:
The resulting dihydrate readily converts into the monohydrate. Both hydrates have a light yellow to yellowish green color. Above 450 ° C, put these in order to give the anhydride.
Properties
Molybdenum ( VI) oxide is present as a white powder that turns yellow when heated and after cooling becomes colorless again. It has the empirical formula MoO 3, a melting point of 795 ° C and a boiling point of 1155 ° C. Molybdenum ( VI) oxide is sparingly soluble in water, but goes in alkaline solution in the molybdate ion MoO42 - over. In dilute solution can be converted by this acidification into the molybdic acid H2MoO4.
It has a relatively high vapor pressure. Therefore, it sublimes appreciably from about 700 ° C, forming shiny, slightly greenish, crystalline baubles.
Molybdenum ( VI) oxide has an orthorhombic crystal structure. It consists of layers of distorted MoO6 octahedra in a orthorhombic crystal. Octahedra are connected at the edges to form chains, which are connected via oxygen atoms and form layers.
Use
Molybdenum ( VI) oxide is the starting material for the synthesis of most other molybdenum compounds, and it serves as an additional enamel for preparing pure molybdenum (for example, by reduction with hydrogen).
It is also a catalyst ( molybdenum trioxide - alumina powder ) for Hydroformier, alkylation, desulfurization and cracking processes in the petrochemical industry and in the manufacture of acrylonitrile.