Iron(II) sulfide

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Iron(II) sulfide
Other names

Iron sulfide, ferrous sulfide, black iron sulfide

Identifiers
CAS number 1317-37-9 YesY
PubChem 10290742
ChemSpider 8466211 YesY
Jmol-3D images {{#if:[Fe+2].[S-2]|Image 1
Properties
Molecular formula FeS
Molar mass 87.910 g/mol
Appearance black solid, sometimes in lumps or powder
Density 4.84 g/cm3
Melting point 1194 °C
Solubility in water negligible (insoluble)
Solubility reacts in acid
Hazards
EU Index Not listed
Main hazards can be pyrophoric
Autoignition temperature variable
Related compounds
Related compounds Iron(II) oxide
Iron disulfide
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Iron(II) sulfide or ferrous sulfide (Br.E. sulphide) is a chemical compound with the formula FeS. In practice, iron sulfides are often non-stoichiometric. Powdered iron sulfide is pyrophoric (ignites spontaneously in air).

Forms of iron sulfide

"Iron sulfide" exists in several distinct forms, which differ in the ratio of sulfur to iron and properties:[1]

  • Pyrrhotite, Fe1-xS, a mineral, which displays ferrimagnetism and crystallizes in monoclinic system. Iron metal shows ferromagnetism; iron sulfides do not.
  • Troilite, FeS, a stoichiometric compound that adopts hexagonal symmetry.
  • Mackinawite, Fe1+xS the least stable form of iron sulfide; mackinawite has a layered structure.
  • Pyrite and marcasite, which are diamagnetic minerals, have the formula FeS2.
  • Greigite (Fe3S4) a ferromagnetic species akin to magnetite (Fe3O4).

Chemical reactions

Iron sulfide reacts with hydrochloric acid, releasing the malodorous (rotten egg smell) and very toxic gas, hydrogen sulfide

FeS + 2 HCl → FeCl2 + H2S

FeS can be obtained by the heating of iron and sulfur:

Fe + S → FeS

Biology and biogeochemistry

Sludge from a pond; the black color is due to metal sulfides

As organic matter decays under low-oxygen (or hypoxic) conditions such as in swamps or dead zones of lakes and oceans, sulfate-reducing bacteria will use the sulfates present in the water to oxidize the organic matter, producing hydrogen sulfide as waste. Some of the hydrogen sulfide will react with metal ions in the water to produce metal sulfides, which are not water soluble. These metal sulfides, such as iron(II) sulfide, are often black or brown, leading to the color of sludge.

Pyrrotite is a waste product of the Desulfovibrio bacteria, a sulfate reducing bacteria.

When eggs are cooked for a long time, the yolk's surface may turn green. This is due to iron(II) sulfide which forms as iron from the yolk meets hydrogen sulfide released from the egg white by the heat.[2] This reaction occurs more rapidly in older eggs as the whites are more alkaline.[3]

The presence of ferrous sulfide as a visible black precipitate in the growth medium peptone iron agar can be used to distinguish between microorganisms that produce the cysteine metabolizing enzyme cysteine desulfhydrase and those that do not. Peptone iron agar contains the amino acid cysteine and a chemical indicator, ferric citrate. The degradation of cysteine releases hydrogen sulfide gas that reacts with the ferric citrate to produce ferrous sulfide.

See also

References

  1. ↑ D., Vaughan; J., Craig (1978), Mineral chemistry of metal sulfides, Cambridge University Press, ISBN 0-521-21489-0 
  2. ↑ Belle Lowe (1937), "The formation of ferrous sulfide in cooked eggs", Experimental cookery from the chemical and physical standpoint, John Wiley & Sons 
  3. ↑ Harold McGee (2004), McGee on Food and Cooking, Hodder and Stoughton 
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