Iron(II) sulfide

Iron(II) sulfide
Names
Other names
Iron sulfide, ferrous sulfide, black iron sulfide, protosulphuret of iron
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.013.881
Properties
FeS
Molar mass 87.910 g/mol
Appearance Gray, sometimes in lumps or powder
Density 4.84 g/cm3
Melting point 1,194 °C (2,181 °F; 1,467 K)
negligible (insoluble)
Solubility reacts in acid
+1074·10−6 cm3/mol
Hazards
Main hazards Source of hydrogen sulfide, can be pyrophoric
NFPA 704
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g., diesel fuelHealth code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentineReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorusSpecial hazards (white): no codeNFPA 704 four-colored diamond
2
1
2
variable
Related compounds
Related compounds
 Iron(II) oxide
Iron disulfide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Iron(II) sulfide or ferrous sulfide (Br.E. sulphide) is one of a family chemical compounds and minerals with the approximate formula FeS. Iron sulfides are often iron-deficient non-stoichiometric. All are black, water-insoluble solids.

Preparation and structure

FeS can be obtained by the heating of iron and sulfur:[1]

Fe + S → FeS

FeS adopts the nickel arsenide structure, featuring octahedral Fe centers and trigonal prismatic sulfide sites.

Reactions

Iron sulfide reacts with hydrochloric acid, releasing hydrogen sulfide

FeS + 2 HCl → FeCl2 + H2S
FeS + H2SO4 → FeO + H2O + SO2

In moist air, iron sulfides oxidize to hydrated ferrous sulfate.

Biology and biogeochemistry

Iron sulfides occur widely in nature in the form of iron–sulfur proteins.

As organic matter decays under low-oxygen (or hypoxic) conditions such as in swamps or dead zones of lakes and oceans, sulfate-reducing bacteria reduce various sulfates present in the water, producing hydrogen sulfide. Some of the hydrogen sulfide will react with metal ions in the water or solid to produce iron or 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.

Pyrrhotite 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 color change is due to iron(II) sulfide, which forms as iron from the yolk reacts with 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. ↑ H. Lux "Iron (II) Sulfide" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1502.
  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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