Litium karbida
Litium karbida, Li2C2, sering dikenal sebagai dilitium asetilida, adalah senyawa kimia dari litium dan karbon, suatu asetilida. Ia merupakan senyawa antara yang dihasilkan selama prosedur penanggalan radiokarbon. Li2C2 adalah salah satu dari serangkaian senyawa litium-karbon yang meliputi senyawa kaya litium: Li4C, Li6C2, Li8C3, Li6C3, Li4C3, Li4C5, dan senyawa interkalasi grafit: LiC6, LiC12, dan LiC18.
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| Nama | |
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| Nama IUPAC (preferensi)
Lithium carbide | |
| Nama IUPAC (sistematis)
Dilithium(1+) ethyne | |
| Nama lain
Dilitium asetilida
Litium dikarbon | |
| Penanda | |
Model 3D (JSmol)
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| 3DMet | {{{3DMet}}} |
| ChemSpider | |
| Nomor EC | |
PubChem CID
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| Nomor RTECS | {{{value}}} |
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| Sifat | |
| Li2C2 | |
| Massa molar | 37,9034 g/mol |
| Densitas | 1,3 g/cm³[1] |
| Titik lebur | > 550°C |
| Kelarutan | tidak larut dalam pelarut organik |
Kecuali dinyatakan lain, data di atas berlaku pada suhu dan tekanan standar (25 °C [77 °F], 100 kPa). | |
 verifikasi (apa ini   ?)
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| Referensi | |
Li2C2 adalah senyawa kaya litium yang paling stabil secara termodinamika[2] dan satu-satunya yang dapat diperoleh langsung dari unsurnya. Ia pertama kali dibuat oleh Moissan, pada tahun 1896[3] yang mereaksikan arang dengan litium karbonat. Senyawa kaya litium lainnya dibuat dengan mereaksikan uap litium dengan hidrokarbon terklorinasi, misalnya CCl4.
Litium karbida kadang-kadang dibingungkan dengan obat litium karbonat, Li2O3, karena kemiripan namanya.
Preparation and chemistry
In the laboratory samples may be prepared by treating acetylene with a solution of lithium in ammonia.
- C2H2 + 2 Li → Li2C2 + H2
Samples prepared in this manner generally are poorly crystalline. Crystalline samples may be prepared by a reaction between molten lithium and graphite at over 1000 °C.[2] Li2C2 can also be prepared by reacting CO2 with molten lithium.
Lithium carbide is hydrolyses readily to form acetylene:
- C2Li2 + H2O → C2H2 + LiOH
Structure
Li2C2 is a Zintl phase compound and exists as a salt, 2Li+C22−. Its reactivity, combined with the difficulty in growing suitable single crystals, has made the determination of its crystal structure difficult. It adopts a distorted anti-fluorite crystal structure, similar to that of rubidium peroxide (Rb2O2) and caesium peroxide (Cs2O2). Each Li atom is surrounded by six carbon atoms from 4 different acetylides, with two acetylides co-ordinating side -on and the other two end-on.[2][4] The observed C-C distance of 120 pm indicates the presence of a C≡C triple bond. At high temperatures Li2C2 transforms reversibly to a cubic anti-fluorite structure.[5]
Use in radiocarbon dating
There are a number of procedures employed, some that burn the sample producing CO2 that is then reacted with lithium, and others where the carbon containing sample is reacted directly with lithium metal.[6] The outcome is the same: Li2C2 is produced, which can then be used to create species easy to mass, like acetylene and benzene.[7] Note that lithium nitride may be formed and this produces ammonia when hydrolyzed, which contaminates the acetylene gas.
References
- ^ R. Juza; V. Wehle; H.-U. Schuster (1967). "Zur Kenntnis des Lithiumacetylids". Zeitschrift für anorganische und allgemeine Chemie. 352 (5–6): 252. doi:10.1002/zaac.19673520506.
- ^ a b c Ruschewitz, Uwe (September 2003). "Binary and ternary carbides of alkali and alkaline-earth metals". Coordination Chemistry Reviews. 244 (1-2): 115–136. doi:10.1016/S0010-8545(03)00102-4.
- ^ H. Moissan Comptes Rendus hebd. Seances Acad. Sci. 122, 362 (1896)
- ^ Juza, Robert; Opp, Karl (November 1951). "Metallamide und Metallnitride, 24. Mitteilung. Die Kristallstruktur des Lithiumamides". Zeitschrift für anorganische und allgemeine Chemie (dalam bahasa German). 266 (6): 313–324. doi:10.1002/zaac.19512660606.
- ^ U. Ruschewitz; R. Pöttgen (1999). "Structural Phase Transition in Li2C2". Zeitschrift für anorganische und allgemeine Chemie. 625 (10): 1599–1603. doi:10.1002/(SICI)1521-3749(199910)625:10<1599::AID-ZAAC1599>3.0.CO;2-J.
- ^ Swart E.R. (1964). "The direct conversion of wood charcoal to lithium carbide in the production of acetylene for radiocarbon dating". Cellular and Molecular Life Sciences. 20: 47. doi:10.1007/BF02146038.
- ^ University of Zurich Radiocarbon Laboratory webpage