Sulfur dioxide
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| Sulfur dioxide | |
|---|---|
| Other names | Sulfur(IV) oxide Sulfurous anhydride |
| Molecular formula | SO2 |
| Molar mass | 64.06 g/mol |
| 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) |
| 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 |
| 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 | Image:Nfpa h3.pngImage:Nfpa f0.pngImage:Nfpa r0.png |
| PEL-TWA (OSHA) | 5 ppm (13 mg/m3) |
| 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 to form sulfuric acid (H2SO4) and thus acid rain.
Contents |
Preparation
Sulfur dioxide is often prepared by burning sulfur in air:
Hydrogen sulfide from crude oil may also be burned.
Sulfide ores such as iron pyrites and sphalerite (zinc blende) may also be used:
When anhydrous CaSO4, is heated with coke and sand in the manufacture of cement, CaSiO3, sulfur dioxide is a by-product.
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 Freon, sulfur dioxide was used as a refrigerant in home refrigerators.
H2SO3 is also called "hydrogen sulfite" or sulfurous acid.
Emissions
According to the 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 EPA’s Acid Rain Program there has been a 33 percent decrease in emissions between 1983 and 2002, partly due to flue gas desulfurization.
In power plants using sulfur containing coal or oil the sulfur dioxide can be chemically bound by flue gas desulfurization . Calcium oxide reacts with sulfur dioxide to form calcium sulfate (gypsum). Most of the gypsum sold in europe comes from this source.
See also
External links
- United States Environmental Protection Agency Sulfur Dioxide page
- International Chemical Safety Card 0074
- IARC Monograph "Sulfur Dioxide and some Sulfites, Bisulfites and Metabisulfites"
- NIOSH Pocket Guide to Chemical Hazards
- Food Intolerance Network - Sulfite factsheet
- Sulfur Dioxide, Molecule of the Monthbg:Серен диоксид
ca:Diòxid de sofre cs:Oxid siřičitý de:Schwefeldioxid es:Dióxido de azufre fi:Rikkidioksidi fr:Dioxyde de soufre it:Diossido di zolfo nl:Zwaveldioxide ja:二酸化硫黄 pl:Tlenek siarki(IV) pt:Dióxido de enxofre ru:Диоксид серы sr:Сумпор диоксид sv:Svaveldioxid uk:Діоксид сірки zh:二氧化硫