Formula FeS Density 4.84 g/cm³ | Molar mass 87.91 g/mol | |
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Related compounds Appearance black solid, sometimes in lumps or powder | ||
Iron ii sulfide
Iron(II) sulfide or ferrous sulfide (Br.E. sulphide) is a chemical compound with the formula FeS. In practice, iron sulfides are often iron-deficient non-stoichiometric. Powdered iron sulfide is pyrophoric (ignites spontaneously in air).
Contents
Chemical reactions
Iron sulfide reacts with hydrochloric acid, releasing the malodorous (rotten egg smell) and very toxic gas, hydrogen sulfide
FeS + 2 HCl → FeCl2 + H2SFeS can be obtained by the heating of iron and sulfur:
Fe + S → FeSDilute sulphuric acid is added over iron(ii) sulphide:
FeS + H2SO4 --> FeO + H2O + SO2
Biology and biogeochemistry
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.
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 is due to iron(II) sulfide which forms as iron from the yolk meets hydrogen sulfide released from the egg white by the heat. This reaction occurs more rapidly in older eggs as the whites are more alkaline.
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.