Silver sulfide

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Silver sulfide
Silver sulfide
Identifiers
CAS number 21548-73-2 YesY
Properties
Molecular formula Ag2S
Molar mass 247.8 g/mol
Appearance Black cubic crystal
Density 7.23 g/cm3
Melting point 825 °C; 1,517 °F; 1,098 K
Solubility in water 8.5−12 mg/L
Solubility soluble in nitric acid and sulfuric acid
Structure
Crystal structure orthogonal
Thermochemistry
Std molar
entropy
So298
144.0 J/mol·K
Std enthalpy of
formation
ΔfHo298
-32.6 kJ/mol
Hazards
Main hazards May cause irritation
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Silver sulfide (Ag
2
S
) is the sulfide of silver. This dense black solid constitutes the tarnish that forms over time on silverware and other silver objects.[1] Silver sulfide is insoluble in all solvents, but is degraded by strong acids. Silver sulfide features a covalent bond, as it is made up of silver (electronegativity of 1.98) and sulfur (electronegativity of 2.58). It is a component of classical qualitative inorganic analysis.[2] When formed on electrical contacts operating in an atmosphere rich in hydrogen sulfide, long filaments known as silver whiskers can form.

Degrading wooden treasure chests aboard sunken galleons can provide the sulfide needed for certain sulfide ion consuming bacteria to produce hydrogen sulfide gas. When combined with silver the hydrogen sulfide gas creates a layer of black silver sulfide patina on the silver, protecting the inner silver from further conversion to silver sulfide. [3]

Structure[edit]

Three forms are known: monoclinic acanthite, stable below 179 °C,[4] body centered cubic so-called argentite, stable above 179 °C,[4] and a high temperature face-centred cubic form stable above 586 °C.[5] The higher temperature forms are electrical conductors.[5] It is found in nature as relatively low temperature mineral acanthite. The name argentite refers to a cubic form, which, due to instability in "normal" temperatures, is found in form of the pseudomorphosis of acanthite after argentite. Acanthite is an important ore of silver. Ag2S is used as a photosensitizer in photography.

References[edit]

  1. ^ Silver, Chemical Element
  2. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419. 
  3. ^ Steven S. Zumdahl; Donald J. DeCoste (201page=505). Chemical Principles, 7th ed. p. 505. 
  4. ^ a b Acanthite Mineralogy Database. Accessed 17 March 2013.
  5. ^ a b Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN 0-19-855370-6