Wikipedia

Sulfur dioxide

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Template:Chembox/SectGeneralTemplate:Chembox/IUPACName
Sulfur dioxide
Sulfur dioxide Sulfur dioxide
Other names Sulfur(IV) oxide
Sulfurous anhydride
Molecular formula SO2
Molar mass 64.054 g mol−1
Appearance colourless gas
CAS number [7446-09-5]
EINECS number 231-195-2
Properties
Density and phase 2.551 g/L, gas
Solubility in water 22 g/100ml (0 °C)

15 g/100ml (10 °C)

11 g/100ml (20 °C)

9.4 g/100 ml (25 °C)

8 g/100ml (30 °C)

6.5 g/100ml (40 °C)

5 g/100ml (50 °C)

4 g/100ml (60 °C)

3.5 g/100ml (70 °C)

3.4 g/100ml (80 °C)

3.5 g/100ml (90 °C)

3.7 g/100ml (100 °C)

Melting point −72.4 °C (200.75 K)
Boiling point −10 °C (263 K)
Critical Point 157.2°C at 7.87 MPa
Acidity (pKa) 1.81
Structure
Molecular shape bent
Dipole moment 1.63 D
Thermodynamic data
Standard enthalpy
of formation ΔfH°gas 		−296.84 kJ mol−1
Standard molar entropy
S°gas 		248.21 J K−1 mol−1
Safety data
EU classification Toxic
R-phrases R23, R34
S-phrases S1/2, S9, S26
S36/37/39, S45
NFPA 704
NFPA 704
safety square
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability (red): no hazard codeInstability (yellow): no hazard codeSpecial hazards (white): no code
3
PEL-TWA (OSHA) 5 ppm (13 mg m−3)
IDLH (NIOSH) 100 ppm
Flash point non-flammable
RTECS number WS4550000
Supplementary data page
Structure and
properties 		n, εr, etc.
Thermodynamic
data 		Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Other cations Selenium dioxide
Tellurium dioxide
Related compounds Sulfur trioxide
Sulfuric acid
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references

Sulfur dioxide (also sulphur dioxide, sulfurous anhydride or sulphurous anhydride) has the chemical formula SO2. The gas is irritating to the lungs and is frequently described as smelling of burning sulfur.

It is produced by volcanoes and in various industrial processes. In particular, poor-quality coal and petroleum contain sulfur compounds, and generate sulfur dioxide when burned: the gas reacts with water and atmospheric oxygen, usually in the presents of a catalyst such as nitrogen dioxide (NO2) to form sulfuric acid (H2SO4) and thus acid rain.

Preparation

Sulfur dioxide is often prepared by burning sulfur in air:

S(s) + O2(g) → SO2(g)

Hydrogen sulfide from crude oil may also be burned.

2H2S(g) + 3O2(g) → 2H2O(g) + 2SO2(g)

Sulfide ores such as iron pyrites and sphalerite (zinc blende) may also be used:

4FeS2(s) + 11O2(g) → 2Fe2O3(s) + 8SO2(g)
2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2

When anhydrous CaSO4 is heated with coke and sand in the manufacture of cement, CaSiO3, sulfur dioxide is a by-product.

2CaSO4(s) + 2SiO2(s) + C(s) → 2CaSiO3(s) + 2SO2(g) + CO2(g)

Uses

Sulfur dioxide is sometimes used as a preservative in alcoholic drinks, or dried apricots and other dried fruits. The preservative is used to maintain the appearance of the fruit rather than prevent rotting. This can give fruit a distinctive chemical taste.

Sulfur dioxide is also a good reductant. In the presence of water, sulfur dioxide is able to decolorize substances that can be reduced by it; thus making it a useful reducing bleach for papers and delicate materials such as clothes.

This bleaching effect normally does not last very long. Oxygen in the atmosphere reoxidizes the reduced dyes, restoring the color. This might explain why older newspapers turn yellow, because paper used for newspaper is naturally yellow.

Sulfur dioxide is also used to make sulfuric acid, being converted to sulfur trioxide, and then to oleum, which is made into sulfuric acid. Sulfur dioxide for this purpose is made when sulfur combines with oxygen. This is called the contact process.

Prior to the development of Freons, sulfur dioxide was used as a refrigerant in home refrigerators.

H2SO3 is also called "hydrogen sulfite" or sulfurous acid.

Emissions

According to the US EPA (as presented by the 2002 World Almanac or in chart form [1]), the following amount of thousands of short tons of Sulfur dioxide were released in the U.S. per year:

*1999 18,867
*1998 19,491
*1997 19,363
*1996 18,859
*1990 23,678
*1980 25,905
*1970 31,161

Due largely to the US EPA’s Acid Rain Program, the U.S. has witnessed a 33 percent decrease in emissions between 1983 and 2002. This improvement resulted from flue gas desulfurization, a technology that enables SO2 to be chemically bound in power plants burning sulfur-containing coal or oil. In particular, calcium oxide reacts with sulfur dioxide to form calcium sulfite:

CaO + SO2 → CaSO3

As of 2006, China is the world's largest Sulfur Dioxide polluter, with 2005 emissions estimated to be 25.49 million tons. This amount represents a 27% increase since 2000, and is roughly comparable with U.S. emissions in 1980.[2]

Aerobic oxidation converts this CaSO3 into CaSO4, gypsum. Most gypsum sold in Europe comes from flue gas desulfurization.

See also

Template:ChemicalSources

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