Magnesium chloride 562007 225842742 2008-07-15T17:33:32Z 145.53.176.195 add. sources solution mining and medical applications {{chembox new | ImageFile = Magnesium chloride.jpg | ImageSize = 200px | IUPACName = Magnesium chloride | SystematicName = | OtherNames = | Section1 = {{Chembox Identifiers | Abbreviations = | CASNo = [7786-30-3] (anhydrous)<br>[7791-18-6] (hexahydrate) | EINECS = | EINECSCASNO = | PubChem = | SMILES = | InChI = | RTECS = OM2975000 | MeSHName = | ChEBI = | KEGG = | ATCCode_prefix = | ATCCode_suffix = | ATC_Supplemental =}} | Section2 = {{Chembox Properties | Formula = MgCl<sub>2</sub> (anhydrous)<br>MgCl<sub>2</sub>.6H<sub>2</sub>O (hexahydrate) | MolarMass = 95.211 g/mol (anhydrous)<br>203.31 g/mol (hexahydrate) | Appearance = white or colourless crystalline solid | Density = 2.32 g/cm³ (anhydrous solid)<br>1.56 g/cm³ (hexahydrate solid) | MeltingPt = 714 °C (987 K) | Melting_notes = | BoilingPt = 1412 °C (1685 K) | Boiling_notes = | Solubility = | SolubleOther = | Solvent = | LogP = | VaporPressure = | HenryConstant = | AtmosphericOHRateConstant = | pKa = | pKb = }} | Section3 = {{Chembox Structure | CrystalStruct = [[Cadmium chloride#Crystal structure|CdCl<sub>2</sub>]] | Coordination = (octahedral, 6-coordinate) | MolShape = }} | Section4 = {{Chembox Thermochemistry | DeltaHf = | DeltaHc = | Entropy = | HeatCapacity = }} | Section5 = {{Chembox Pharmacology | AdminRoutes = | Bioavail = | Metabolism = | HalfLife = | ProteinBound = | Excretion = | Legal_status = | Legal_US = | Legal_UK = | Legal_AU = | Legal_CA = | PregCat = | PregCat_AU = | PregCat_US = }} | Section6 = {{Chembox Explosive | ShockSens = | FrictionSens = | ExplosiveV = | REFactor = }} | Section7 = {{Chembox Hazards | EUClass = | EUIndex = | MainHazards = irritant | NFPA-H = | NFPA-F = | NFPA-R = | NFPA-O = | RPhrases = | SPhrases = {{S22}},{{S23}},{{S24}},{{S25}} | RSPhrases = | FlashPt = | Autoignition = | ExploLimits = | LD50 = | PEL = }} | Section8 = {{Chembox Related | OtherAnions = [[Magnesium fluoride]]<br> [[Magnesium bromide]]<br> [[Magnesium iodide]] | OtherCations = [[beryllium chloride]]<br>[[calcium chloride]] | OtherFunctn = | Function = | OtherCpds = }} }} '''Magnesium chloride''' is the name for the [[chemical compound]]s with the [[chemical formula|formula]]s MgCl<sub>2</sub> and its various [[water of hydration|hydrate]]s MgCl<sub>2</sub>(H<sub>2</sub>O)<sub>x</sub>. These salts are typical ionic halides, being highly soluble in water. The hydrated magnesium chloride can be extracted from [[brine]] or [[sea water]]. Magnesium chloride as the natural mineral Bischofite is also extrated (solution mining) out of ancient seabeds, for example the Zechstein seabed in NW Europe. [[Anhydrous]] magnesium chloride is the principal precursor to magnesium metal, which is produced on a large scale. ==Structure, preparation, basic properties== MgCl<sub>2</sub> crystallizes in the [[cadmium chloride]] motif, which features octahedral Mg. A variety of hydrates are known with the formula MgCl<sub>2</sub>(H<sub>2</sub>O)<sub>x</sub>, and each loses water with increasing temperature: x = 12 (-16.4 °C), 8 (-3.4 °C), 6 (116.7 °C), 4 (181 °C), 2 (ca. 300 °C).<ref>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.</ref> In the hexahydrate, the Mg<sup>2+</sup> remains [[Octahedral molecular geometry|octahedral]], but is coordinated to six water [[ligand]]s.<ref>Wells, A. F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.</ref> As suggested by the existence of several hydrates, anhydrous MgCl<sub>2</sub> is a [[Lewis acid]], although a relatively weak one. In the [[Dow process]], magnesium chloride is regenerated from magnesium hydroxide using [[hydrochloric acid]]: :[[Magnesium hydroxide|Mg(OH)<sub>2</sub>]]([[solid|s]]) + 2 HCl → MgCl<sub>2</sub>(aq) + 2 [[water|H<sub>2</sub>O]]([[liquid|l]]) It can also be prepared from [[magnesium carbonate]] by a similar reaction. In most of its derivatives, MgCl<sub>2</sub> forms octahedral complexes. Derivatives with tetrahedral Mg<sup>2+</sup> are less common. Examples include salts of ([[tetraethylammonium]])<sub>2</sub>MgCl<sub>4</sub> and [[adduct]]s such as MgCl<sub>2</sub>([[TMEDA]].<ref>N. N. Greenwood, A. Earnshaw, ''Chemistry of the Elements'', Pergamon Press, 1984.</ref> ==Applications== Magnesium chloride serves as precursor to other magnesium compounds, for example by precipitation: :MgCl<sub>2</sub>([[aqueous|aq]]) + [[calcium hydroxide|Ca(OH)<sub>2</sub>]](aq) → [[magnesium hydroxide|Mg(OH)<sub>2</sub>]]([[solid|s]]) + [[calcium chloride|CaCl<sub>2</sub>]](aq) It can be [[electrolysis|electrolysed]] to give [[magnesium]] metal:<ref name="Hill">Hill, Petrucci, McCreary, Perry, "General Chemistry", 4th ed., Pearson/Prentice Hall, Upper Saddle River, New Jersey, USA.</ref> :MgCl<sub>2</sub>([[liquid|l]]) → Mg([[liquid|l]]) + Cl<sub>2</sub>([[gas|g]]) This process is practiced on a substantial scale: In 1990, US production was around one million [[tonne]]s, with a bulk price around $180 per tonne.{{Fact|date=May 2007}} The thermal dehydration of the hydrates MgCl<sub>2</sub>(H<sub>2</sub>O)<sub>x</sub> (x = 6, 12) does not occur straightforwardly.<ref>see notes in Rieke, R. D.; Bales, S. E.; Hudnall, P. M.; Burns, T. P.; Poindexter, G S. “Highly Reactive Magnesium for the Preparation of Grignard Reagents: 1-Norbornane Acid” Organic Syntheses, Collected Volume 6, p.845 (1988). http://www.orgsyn.org/orgsyn/pdfs/CV6P0845.pdf</ref> Magnesium chloride is used for a variety of other applications besides the production of [[magnesium]]: the manufacture of [[textiles]], [[paper]], [[fireproofing|fireproofing agents]], [[cement]]s and [[refrigeration]] brine,<ref name="Hill" /> and dust and erosion control. Mixed with hydrated magnesium oxide, magnesium chloride forms a hard material called [[Sorel cement]]. Magnesium chloride is also used as an important component in the [[polymerase chain reaction]], a procedure used to amplify DNA fragments. Magnesium chloride is also used in several medical and topical (skin related) aplications. ===Culinary use=== Magnesium chloride is an important coagulant used in the preparation of [[tofu]] from [[soy milk]]. In Japan it is sold as ''nigari'' (the term is derived from the Japanese word for "bitter"), a white powder produced from seawater after the [[sodium chloride]] has been removed, and the water evaporated. In China it is called "lushui"(卤水 in Chinese). Nigari or Lushui consists mostly of magnesium chloride, with some [[magnesium sulfate]] and other trace elements. It is also an ingredient in baby formula milk. ===Use as an anti-icer=== A number of state highway departments throughout the United States have decreased the use of [[rock salt]] and sand on roadways and have increased the use of liquid magnesium chloride as a de-icer or anti-icer. Magnesium chloride is much less toxic to plant life surrounding highways and airports, and is less corrosive to concrete and steel (and other iron alloys) than sodium chloride. The liquid magnesium chloride is sprayed on dry pavement (tarmac) prior to precipitation or wet pavement prior to freezing temperatures in the winter months to prevent snow and ice from adhering and bonding to the roadway. The application of anti-icers is utilized in an effort to improve highway safety. Magnesium chloride is also sold in crystal form for household and business use to de-ice sidewalks and driveways. In these applications, the compound is applied after precipitation has fallen or ice has formed, instead of previously. The use of this compound seems to show an improvement in driving conditions during and after freezing precipitation yet it seems to be negatively affecting electric utilities. Two main issues have been raised regarding the anti-icer magnesium chloride as it relates to electric utilities: contamination of insulators causing tracking and arcing across them, and corrosion of steel and [[aluminium]] poles and pole hardware. ===Use in dust and erosion control=== Road departments and private industry may apply liquid or powdered magnesium chloride to control dust and erosion on unimproved (dirt or gravel) roads and dusty job sites such as quarries. Its [[hygroscopy]] makes it absorb moisture from the air, controlling the number of small particles which become airborne. Similarly, owners of indoor arenas (e.g. for horse riding) may apply magnesium chloride to sand or other floor materials to control dust. ===Use in hydrogen storage=== Magnesium chloride has shown promise as a storage material for [[hydrogen]]. [[Ammonia]], which is rich in hydrogen atoms, is used as an intermediate storage material. Ammonia can be effectively absorbed onto solid magnesium chloride, forming Mg(NH<sub>3</sub>)<sub>6</sub>Cl<sub>2</sub>. Ammonia is released by mild heat, and is then passed through a catalyst to give hydrogen gas. == References == <references /> * ''Handbook of Chemistry and Physics'', 71st edition, CRC Press, Ann Arbor, Michigan, 1990. == External links == * [http://www.usda.gov/rus/electric/engineering/2001/magnesium_chloride.htm Magnesium Chloride as a De-Icing Agent] * [http://www.mgwater.com] [[Category:Chlorides]] [[Category:Magnesium compounds]] [[Category:Metal halides]] [[Category:Deliquescent substances]] [[ca:Clorur de magnesi]] [[cs:Chlorid hořečnatý]] [[da:Magnesiumchlorid]] [[de:Magnesiumchlorid]] [[es:Cloruro de magnesio]] [[fr:Chlorure de magnésium]] [[gl:Cloruro de magnesio]] [[hu:Magnézium-klorid]] [[nl:Magnesiumchloride]] [[ja:塩化マグネシウム]] [[pl:Chlorek magnezu]] [[pt:Cloreto de magnésio]] [[ru:Хлорид магния]] [[sk:Chlorid horečnatý]] [[sr:Магнезијум хлорид]] [[sv:Magnesiumklorid]] [[zh:氯化镁]]