Silver sulfide

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Silver sulfide
Ball-and-stick model of silver sulfide
Sample of silver sulfide
Identifiers
CAS number 21548-73-2 YesY
PubChem 166738 YesY
ChemSpider 145878 YesY
UNII 9ZB10YHC1C YesY
EC-number 244-438-2
Jmol-3D images Image 1
Properties
Molecular formula Ag2S
Molar mass 247.80 g mol−1
Appearance Grayish-black crystal
Odor Odorless
Density 7.234 g/cm3 (25 °C)[1][2]
7.12 g/cm3 (117 °C)[3]
Melting point 836 °C (1,537 °F; 1,109 K)[1]
Solubility in water 0.14 mg/L (20 °C)[4][5]
Solubility product, Ksp 6·10−51[4]
Solubility Soluble in aq. HCN, aq. citric acid with KNO3
Insoluble in acids, alkalies, aqueous ammoniums[6]
Structure
Crystal structure Monoclinic, mP12 (α-form)
Cubic, cI8 (β-form)
Cubic, cF12 (γ-form)[3][7]
Space group P21/n, No. 14 (α-form)[7]
Im3m, No. 229 (β-form)
Fm3m, No. 225 (γ-form)[3]
Point group 2/m (α-form)[7]
4/m 3 2/m (β-form, γ-form)[3]
Lattice constant a = 4.23 Å, b = 6.91 Å, c = 7.87 Å (α-form)[7]
Lattice constant α = 90°, β = 99.583°, γ = 90°
Coordination
geometry
Tetrahedral (Ag+)
Thermochemistry
Specific
heat capacity
C
76.57 J/mol·K[8]
Std molar
entropy
So298
143.93 J/mol·K[8]
Std enthalpy of
formation
ΔfHo298
−32.59 kJ/mol[8]
Gibbs free energy ΔG −40.71 kJ/mol[8]
Hazards
GHS pictograms The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)[2]
GHS signal word Warning
GHS hazard statements H315, H319, H335[2]
GHS precautionary statements P261, P305+351+338[2]
EU classification Irritant Xi
R-phrases R36/37/38
S-phrases S26, S36
Main hazards May cause irritation
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g., sodium chloride Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Silver sulfide (Ag
2
S
) is the sulfide of silver. It useful as a photosensitizer in photography.

Properties[edit]

This dense black solid constitutes the tarnish that forms over time on silverware and other silver objects.[9] 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.[10] 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. [11]

Structure[edit]

Three forms are known: monoclinic acanthite (α-form), stable below 179 °C, body centered cubic so-called argentite (β-form), stable above 180 °C, and a high temperature face-centred cubic (γ-form) stable above 586 °C.[7] The higher temperature forms are electrical conductors. 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.

References[edit]

  1. ^ a b Lide, David R., ed. (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4200-9084-0. 
  2. ^ a b c d Sigma-Aldrich Co., Silver sulfide. Retrieved on 2014-07-13.
  3. ^ a b c d Tonkov, E. Yu (1992). High Pressure Phase Transformations: A Handbook 1. Gordon and Breach Science Publishers. p. 13. ISBN 2-88124-761-X. 
  4. ^ a b "Solubility Products". http://www.saltlakemetals.com. Utah, USA: Salt Lake Metals. Retrieved 2014-07-13. 
  5. ^ a b "MSDS of Silver Sulfide". http://www.saltlakemetals.com. Utah, USA: Salt Lake Metals. Retrieved 2014-07-13. 
  6. ^ Comey, Arthur Messinger; Hahn, Dorothy A. (1921-02). A Dictionary of Chemical Solubilities: Inorganic (2nd ed.). New York: The MacMillan Company. p. 835.  Check date values in: |date= (help)
  7. ^ a b c d e "Silver sulfide (Ag2S) crystal structure" 41C. Springer Berlin Heidelberg. 1998. pp. 1–4. doi:10.1007/10681727_86. ISBN 978-3-540-31360-1. 
  8. ^ a b c d Pradyot, Patnaik (2003). Handbook of Inorganic Chemicals. The McGraw-Hill Companies, Inc. p. 845. ISBN 0-07-049439-8. 
  9. ^ "Silver". http://www.chemistryexplained.com. Advameg, Inc. Retrieved 2014-07-13. 
  10. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419. 
  11. ^ Zumdahl, Steven S.; DeCoste, Donald J. (2013). Chemical Principles (7th ed.). p. 505. ISBN 978-1-111-58065-0. 

External links[edit]

Tarnishing of Silver: A Short Review V&A Conservation Journal