Hydrogen sulfide

Hydrogen sulfide
Systematic name Hydrogen sulfide
Other names	Dihydrogen monosulfide Dihydrogen sulfide Sewer gas Stink damp Sulfane Sulfurated hydrogen Sulfureted hydrogen Sulfuretted hydrogen Sulfur hydride
Identifiers
CAS number	7783-06-4
PubChem	402
EC number	231-977-3
KEGG	C00283
MeSH	Hydrogen+sulfide
ChEBI	CHEBI:16136
RTECS number	MX1225000
SMILES	S
InChI InChI=1/H2S/h1H2
Beilstein Reference	3535004
Gmelin Reference	303
3DMet	B01206
Properties
Molecular formula	H2S
Molar mass	34.08 g mol-1
Appearance	Colorless gas
Odor	faint rotten egg
Density	1.363 g dm-3
Melting point	-82 °C, 191 K, -116 °F
Boiling point	-60 °C, 213 K, -76 °F
Solubility in water	4 g dm-3 (at 20 °C)
Vapor pressure	1740 kPa (at 21 °C)
Acidity (pKa)	7.0
Basicity (pKb)	6.95
Refractive index (nD)	1.000644 (0 °C)
Structure
Molecular shape	Bent
Dipole moment	0.97 D
Thermochemistry
Std enthalpy of formation ΔfHo298	−21 kJ·mol−1
Standard molar entropy So298	206 J·mol−1·K−1
Specific heat capacity, C	1.003 J K-1 g-1
Hazards
EU classification	F+ T+ N
EU Index	016-001-00-4
NFPA 704	4 4 0
R-phrases	Template:R12, Template:R26, R50
S-phrases	(S1/2), Template:S9, Template:S16, S36, Template:S38, S45, S61
Flash point	-82.4 °C.
Autoignition temperature	232 °C
Explosive limits	4.3–46%
Related compounds
Related hydrogen chalcogenides	Water Hydrogen selenide Hydrogen telluride Hydrogen polonide Hydrogen disulfide Sulfanyl
Related compounds	Phosphine
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Hydrogen sulfide (British English: hydrogen sulphide) is the chemical compound with the formula H₂S, is a colorless, toxic, flammable gas that is responsible for the foul smell of rotten eggs and flatulence. It often results when bacteria break down organic matter in the absence of oxygen. This happens in swamps, and sewers (alongside the process of anaerobic digestion). It also occurs in volcanic gases, natural gas and some well waters. This is the smell that people often think to be that of sulfur. But sulfur itself does not smell.

Hydrogen sulfide is also known as sulfane, sulfur hydride, sour gas, sulfurated hydrogen, hydrosulfuric acid, sewer gas and stink damp. IUPAC accepts the names "hydrogen sulfide" and "sulfane". When people speak of more complicated compounds they always use the term "sulfane".

Occurrence

Deposit of sulfur on a rock, caused by volcanic gases containing hydrogen sulfide

Small amounts of hydrogen sulfide can be found in crude petroleum. Sour natural gas can contain up to 28%. But, sour natural gas must be cleaned before it can enter a long distance pipeline. Pipelines limit hydrogen sulfide to 3 grains per thousand cubic feet of natural gas. Volcanoes and hot springs give off some H₂S, where it probably is made by the hydrolysis of sulfide minerals, i.e. MS + H₂O to give MO + H₂S.

Normal average concentration in clean air is about 0.0001-0.0002 ppm.

Safety

Hydrogen sulfide is a highly toxic and flammable gas. Because it is heavier than air it tends to accumulate at the bottom of poorly ventilated spaces.

Toxicity

Hydrogen sulfide is considered a broad-spectrum poison, meaning that it can poison several different systems in the body, although the nervous system is most affected. The toxicity of H₂S is comparable with that of hydrogen cyanide.

Reference

• "Hydrogen Sulfide", Committee on Medical and Biological Effects of Environmental Pollutants, University Park Press, 1979, Baltimore. ISBN 0-8391-0127-9

Other websites

• International Chemical Safety Card 0165
• Concise International Chemical Assessment Document 53
• National Pollutant Inventory - Hydrogen sulfide fact sheet
• NIOSH Pocket Guide to Chemical Hazards
• MSDS safety data sheet
• Abstract of survey article on H₂S as used by the body, by P. Kamoun
• Computational Chemistry Wiki