Silver cyanide is the chemical compound with the formula AgCN. It is a white salt that is precipitated upon treatment of solutions containing Ag+ with cyanide, which is used in some schemes to recover silver from solution. Silver cyanide is used in silver-plating.
 40 grams of silver cyanide on a scale.
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| Names | |
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| IUPAC name
Silver cyanide
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| Other names
Argentous cyanide
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| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.007.317 |
| EC Number |
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PubChem CID
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| RTECS number |
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| UNII | |
| UN number | 1684 |
CompTox Dashboard (EPA)
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| Properties | |
| AgCN | |
| Molar mass | 133.8856 g/mol |
| Appearance | colorless, gray (impure) crystals |
| Odor | odorless |
| Density | 3.943 g/cm3 |
| Melting point | 335 °C (635 °F; 608 K) (decomposes) |
| 0.000023 g/100 mL (20 °C) | |
Solubility product (Ksp)
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5.97×10−17[1] |
| Solubility | soluble in concentrated ammonia, boiling nitric acid, ammonium hydroxide, KCN insoluble in alcohol, dilute acid |
| −43.2·10−6 cm3/mol | |
Refractive index (nD)
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1.685 |
| Structure | |
| hexagonal | |
| linear | |
| Thermochemistry | |
Std molar
entropy (S⦵298) |
84 J·mol−1·K−1[2] |
Std enthalpy of
formation (ΔfH⦵298) |
146 kJ·mol−1[2] |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards
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toxic |
| GHS labelling: | |
  
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| Danger | |
| H290, H300, H310, H315, H318, H330, H410 | |
| P234, P260, P262, P264, P270, P271, P273, P280, P284, P301+P310, P302+P350, P302+P352, P304+P340, P305+P351+P338, P310, P320, P321, P322, P330, P332+P313, P361, P362, P363, P390, P391, P403+P233, P404, P405, P501 | |
| NFPA 704 (fire diamond) | |
| Flash point | 320 °C (608 °F; 593 K) |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose)
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123 mg/kg (oral, rat) |
| Related compounds | |
Other anions
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AgCl |
Other cations
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NaCN Copper(I) cyanide |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Structure
editThe structure of silver cyanide consists of -[Ag-CN]- chains in which the linear two-coordinate Ag+ ions are bridged by the cyanide ions,[3] typical of silver(I) and other d10 ions. This is the same binding mode as seen in the more famous case of Prussian blue. These chains then pack hexagonally with adjacent chains offset by +/- 1/3 of the c lattice parameter. This is the same as the structure adopted by the high temperature polymorph of copper(I) cyanide. The silver to carbon and silver to nitrogen bond lengths in AgCN are both ~2.06 Å[4] and the cyanide groups show head-to-tail disorder.[5]
Reactions
editAgCN precipitates upon the addition of sodium cyanide to a solution containing Ag+. On the addition of further cyanide, the precipitate dissolves to form linear [Ag(CN)2]−(aq) and [Ag(CN)3]2−(aq). Silver cyanide is also soluble in solutions containing other ligands such as ammonia or tertiary phosphines.
Silver cyanides form structurally complex materials upon reaction with other anions.[6] Some silver cyanides are luminescent.[7]
Uses
edit"Cyanidation" is widely used in the isolation of silver from its ores. Partial purification of silver compounds is usually effected by froth flotation. The silver ion is then separated from the skimmed froth with cyanide, yielding a solution of [Ag(CN)2]−. The silver metal can then be plated out by electrolysis of such solutions.[8]
Both AgCN and KAg(CN)2 have been used in silver-plating solutions since at least 1840 when the Elkington brothers patented their recipe for a silver-plating solution. A typical, traditional silver-plating solution would contain 15-40 g·L−1 KAg(CN)2 , 12-120 g·L−1 KCN and 15 g·L−1 K2CO3.[9]
See also
editReferences
edit- ^ John Rumble (June 18, 2018). CRC Handbook of Chemistry and Physics (99 ed.). CRC Press. pp. 5–189. ISBN 978-1138561632.
- ^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN 978-0-618-94690-7.
- ^ Bowmaker, Graham A.; Kennedy, Brendan J.; Reid, Jason C. (1998). "Crystal Structures of AuCN and AgCN and Vibrational Spectroscopic Studies of AuCN, AgCN, and CuCN". Inorg. Chem. 37 (16): 3968–3974. doi:10.1021/ic9714697. PMID 11670511.
- ^ Hibble, S. J.; Cheyne, S. M.; Hannon, A. C.; Eversfield, S. G. (2002). "Beyond Bragg scattering: the structure of AgCN determined from total neutron diffraction". Inorganic Chemistry. 41 (5): 1042–1044. doi:10.1021/ic015610u. PMID 11874335.
- ^ Bryce, David L.; Wasylishen, Roderick E. (2002). "Insight into the Structure of Silver Cyanide from 13C and 15N Solid-State NMR Spectroscopy". Inorganic Chemistry. 41 (16): 4131–4138. doi:10.1021/ic0201553. ISSN 0020-1669. PMID 12160400.
- ^ Urban, Victoria; Pretsch, Thorsten; Hartl, Hans (2005-04-29). "From AgCN Chains to a Fivefold Helix and a Fishnet-Shaped Framework Structure". Angewandte Chemie International Edition. 44 (18): 2794–2797. doi:10.1002/anie.200462793. ISSN 1433-7851. PMID 15830404.
- ^ Omary, Mohammad A.; Webb, Thomas R.; Assefa, Zerihun; Shankle, George E.; Patterson, Howard H. (1998). "Crystal Structure, Electronic Structure, and Temperature-Dependent Raman Spectra of Tl[Ag(CN)2]: Evidence for Ligand-Unsupported Argentophilic Interactions". Inorganic Chemistry. 37 (6): 1380–1386. doi:10.1021/ic970694l. ISSN 0020-1669. PMID 11670349.
- ^ Etris, S. F. (2010). "Silver and Silver Alloys". Kirk-Othmer Encyclopedia of Chemical Technology. pp. 1–43. doi:10.1002/0471238961.1909122205201809.a01.pub3. ISBN 978-0471238966.
- ^ Blair, Alan (2000). "Silver plating". Metal Finishing. 98 (1): 298–303. doi:10.1016/S0026-0576(00)80339-6.