 | |
| Names | |
|---|---|
| Other names Arsenic(V) oxide Neutral arsenic oxide (2:5) Arsenic anhydride | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider |
|
| ECHA InfoCard | 100.013.743 |
| EC Number |
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| RTECS number |
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| UNII | |
| UN number | 1559 |
| |
| |
| Properties | |
| As2O5 | |
| Molar mass | 229.8402 g/mol |
| Appearance | whitehygroscopic powder |
| Density | 4.32 g/cm3 |
| Melting point | 315 °C (599 °F; 588 K) (decomposes) |
| 59.5 g/100 mL (0 °C) 65.8 g/100 mL (20 °C) 8.20 g/100 mL (100 °C) | |
| Solubility | soluble inalcohol |
| Acidity (pKa) | 7 |
| Hazards | |
| GHS labelling: | |
   | |
| Danger | |
| H301,H331,H350,H410 | |
| P201,P202,P261,P264,P270,P271,P273,P281,P301+P310,P304+P340,P308+P313,P311,P321,P330,P391,P403+P233,P405,P501 | |
| NFPA 704 (fire diamond) | |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 8 mg/kg (rat, oral) |
| NIOSH (US health exposure limits): | |
PEL (Permissible) | [1910.1018] TWA 0.010 mg/m3[1] |
REL (Recommended) | Ca C 0.002 mg/m3 [15-minute][1] |
IDLH (Immediate danger) | Ca [5 mg/m3 (as As)][1] |
| Related compounds | |
Othercations | Phosphorus pentoxide Antimony pentoxide |
Related compounds | Arsenic trioxide Arsenic acid |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Arsenic pentoxide is theinorganic compound with the formula As2O5.[2] This glassy, white,deliquescent solid is relatively unstable, consistent with the rarity of the As(V) oxidation state. More common, and far more important commercially, isarsenic(III) oxide (As2O3). All inorganic arsenic compounds are highly toxic and thus find only limited commercial applications.
The structure consists of tetrahedral {AsO4} and octahedral {AsO6} centers linked by sharing corners.[3] The structure differs from that of the correspondingphosphorus(V) oxide; as a result, although there is still a solid solution with that oxide, it only progresses to the equimolar point, at which point phosphorus has substituted for arsenic in all of its tetrahedral sites. Likewise, arsenic pentoxide can also dissolve up to an equimolar amount ofantimony pentoxide, as antimony substitutes for arsenic only in its octahedral sites.[4]
 |  |  |
| As coordination | unit cell | cell packing |
Pierre Macquer found a crystallizable salt which he called "sel neutre arsenical". This salt was the residue obtained after distillingnitric acid from a mixture ofpotassium nitrate andarsenic trioxide. Previously Paracelsus heated a mixture of arsenic trioxide and potassium nitrate. He applied the term "arsenicum fixum" to the product. A.Libavius called the same product "butyrum arsenici" (butter of arsenic), although this term was actually used for arsenic trichloride. The products that Paracelsus and Libavius found were all impure alkali arsenates.[5]Scheele prepared a number of arsenates by the action of arsenic acid on the alkalies. One of the arsenates that he prepared, was arsenic pentoxide.[6] The water in the alkalies evaporated at 180˚C, and the arsenic pentoxide was stable below 400˚C.[5]
Arsenic pentoxide can be crystallized by heating As2O3 under oxygen. This reaction is reversible:[3]
Strongoxidizing agents such asozone,hydrogen peroxide, andnitric acid convert arsenic trioxide to the pentoxide.
Arsenic acid can be generated via routine processing of arsenic compounds including the oxidation of arsenic and arsenic-containing minerals in air. Illustrative is the roasting oforpiment, a typical arsenic sulfide ore:[7]
Like all inorganic arsenic compounds, the pentoxide is highly toxic. Its reduced derivative arsenite, which is an As(III) compound, is even more toxic since it has a high affinity for thiol groups ofcysteine residues in proteins.
It is classified as anextremely hazardous substance in the United States as defined in Section 302 of the U.S.Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.[8]
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