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Sulphur dioxide

Sulfur dioxide
Skeletal formula sulfur dioxide with assorted dimensions
Spacefill model of sulfur dioxide
Names
IUPAC name
Sulfur dioxide
Other names
Sulfurous anhydride
Sulfur(IV) oxide
Identifiers
7446-09-5 YesY
3D model (Jmol) Interactive image
3535237
ChEBI CHEBI:18422 YesY
ChEMBL ChEMBL1235997 N
ChemSpider 1087 YesY
ECHA InfoCard 100.028.359
EC Number 231-195-2
E number E220 (preservatives)
1443
KEGG D05961 YesY
MeSH Sulfur+dioxide
PubChem 1119
RTECS number WS4550000
UNII 0UZA3422Q4 YesY
UN number 1079, 2037
Properties
SO
2
Molar mass 64.066 g mol−1
Appearance Colorless gas
Odor Pungent; similar to a just-struck match
Density 2.6288 kg m−3
Melting point −72 °C; −98 °F; 201 K
Boiling point −10 °C (14 °F; 263 K)
94 g/L
Vapor pressure 237.2 kPa
Acidity (pKa) 1.81
Basicity (pKb) 12.19
−18.2·10−6 cm3/mol
Viscosity 0.403 cP (at 0 °C)
Structure
C2v
Digonal
Dihedral
1.62 D
Thermochemistry
248.223 J K−1 mol−1
−296.81 kJ mol−1
Hazards
Toxic T
R-phrases R23, R34, R50
S-phrases (S1/2), S9, S26, S36/37/39, S45
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Lethal dose or concentration (LD, LC):
3000 ppm (mouse, 30 min)
2520 ppm (rat, 1 hr)
993 ppm (rat, 20 min)
611 ppm (rat, 5 hr)
764 ppm (mouse, 20 min)
1000 ppm (human, 10 min)
3000 ppm (human, 5 min)
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 5 ppm (13 mg/m3)
REL (Recommended)
TWA 2 ppm (5 mg/m3) ST 5 ppm (13 mg/m3)
IDLH (Immediate danger)
100 ppm
Related compounds
Related sulfur oxides
Sulfur monoxide
Sulfur trioxide
Related compounds
Ozone

Selenium dioxide
Sulfurous acid
Tellurium dioxide

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Selenium dioxide
Sulfurous acid
Tellurium dioxide

Sulfur dioxide (also sulphur dioxide) is the chemical compound with the formula SO
2
. At standard atmosphere, it is a toxic gas with a pungent, irritating smell. The triple point is 197.69 K and 1.67 kPa. It is released naturally by volcanic activity.

Sulfur dioxide was used by the Romans in winemaking when they discovered that burning sulfur candles inside empty wine vessels kept them fresh and free from vinegar smell.

SO2 is a bent molecule with C2vsymmetry point group. A valence bond theory approach considering just s and p orbitals would describe the bonding in terms of resonance between two resonance structures.

The sulfur–oxygen bond has a bond order of 1.5. There is support for this simple approach that does not invoke d orbital participation. In terms of electron-counting formalism, the sulfur atom has an oxidation state of +4 and a formal charge of +1.

It is found on Earth and exists in very small concentrations and in the atmosphere at about 1 ppm.

On other planets, it can be found in various concentrations, the most significant being the atmosphere of Venus, where it is the third-most significant atmospheric gas at 150 ppm. There, it condenses to form clouds, and is a key component of chemical reactions in the planet's atmosphere and contributes to global warming. It has been implicated as a key agent in the warming of early Mars, with estimates of concentrations in the lower atmosphere as high as 100 ppm, though it only exists in trace amounts. On both Venus and Mars, its primary source, like on Earth, is thought to be volcanic. The atmosphere of Io is 90% sulfur dioxide and trace amounts are thought to also exist in the atmosphere of Jupiter.


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