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| Names | |
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Other names
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| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChEMBL | |
| ChemSpider |
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| ECHA InfoCard | 100.029.176 |
| EC Number |
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| E number | E511(acidity regulators, ...) |
| 9305 | |
| RTECS number |
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| UNII |
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| Properties | |
| MgCl2 | |
| Molar mass | 95.211 g/mol (anhydrous) 203.31 g/mol (hexahydrate) |
| Appearance | white or colourless crystalline solid |
| Density | 2.32 g/cm3 (anhydrous) 1.569 g/cm3 (hexahydrate) |
| Melting point | 714 °C (1,317 °F; 987 K) anhydrous 117 °C (243 °F; 390 K) hexahydrate on rapid heating; slow heating leads to decomposition from 300 °C (572 °F; 573 K) |
| Boiling point | 1,412 °C (2,574 °F; 1,685 K) |
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| Solubility | slightly soluble inacetone,pyridine |
| Solubility inethanol | 7.4 g/(100 mL) (30 °C) |
| −47.4·10−6 cm3/mol | |
Refractive index (nD) | 1.675 (anhydrous) 1.569 (hexahydrate) |
| Structure | |
| CdCl2 | |
| (octahedral, 6-coordinate) | |
| Thermochemistry | |
| 71.09 J/(mol·K) | |
Std molar entropy(S⦵298) | 89.88 J/(mol·K) |
Std enthalpy of formation(ΔfH⦵298) | −641.1 kJ/mol |
Gibbs free energy(ΔfG⦵) | −591.6 kJ/mol |
| Pharmacology | |
| A12CC01 (WHO) B05XA11 (WHO) | |
| Hazards[1] | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | Irritant |
| GHS labelling: | |
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| Warning | |
| H319,H335 | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 2800 mg/kg (oral, rat) |
| Safety data sheet (SDS) | ICSC 0764 |
| Related compounds | |
Otheranions | |
Othercations | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Magnesium chloride is aninorganic compound with theformulaMgCl2. It formshydratesMgCl2·nH2O, wheren can range from 1 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which occur in nature, have a variety of practical uses.Anhydrous magnesium chloride is the principal precursor to magnesium metal, which is produced on a large scale. Hydrated magnesium chloride is the form most readily available.[2]
Magnesium chloride can be extracted frombrine orsea water. In North America and South America, it is obtained primarily fromGreat Salt Lake brine. In theJordan Valley, it is obtained from theDead Sea. The mineralbischofite (MgCl2·6H2O) is extracted (by solution mining) out of ancient seabeds, for example, theZechstein seabed in northwest Europe. Some deposits result from high content of magnesium chloride in the primordial ocean.[3] Some magnesium chloride is made from evaporation of seawater.
In theDow process, magnesium chloride is regenerated from magnesium hydroxide usinghydrochloric acid:
It can also be prepared frommagnesium carbonate by a similar reaction.
MgCl2 crystallizes in thecadmium chlorideCdCl2 motif, therefore it loses water upon heating:n = 12 (−16.4 °C), 8 (−3.4 °C), 6 (116.7 °C), 4 (181 °C), 2 (about 300 °C).[4] In the hexahydrate, theMg2+ is alsooctahedral, being coordinated to six waterligands.[5] The octahydrate and the dodecahydrate can be crystallized from water below 298K. As verified byX-ray crystallography, these "higher" hydrates also feature [Mg(H2O)6]2+ ions.[6] A decahydrate has also been crystallized.[7]
AnhydrousMgCl2 is produced industrially by heating thecomplex salt named hexamminemagnesium dichloride[Mg(NH3)6]2+(Cl−)2.[2] The thermal dehydration of the hydratesMgCl2·nH2O (n = 6, 12) does not occur straightforwardly.[8]
As suggested by the existence of hydrates, anhydrousMgCl2 is aLewis acid, although a weak one. One derivative istetraethylammonium tetrachloromagnesate[N(CH2CH3)4]2[MgCl4]. TheadductMgCl2(TMEDA) is another.[9] In thecoordination polymer with the formulaMgCl2(dioxane)2, Mg adopts an octahedral geometry.[10] The Lewis acidity of magnesium chloride is reflected in itsdeliquescence, meaning that it attracts moisture from the air to the extent that the solid turns into a liquid.
AnhydrousMgCl2 is the main precursor to metallic magnesium. The reduction ofMg2+ into metallic Mg is performed byelectrolysis inmolten salt.[2][11] As it is also the case foraluminium, an electrolysis in aqueous solution is not possible as the produced metallic magnesium would immediately react with water, or in other words that the waterH+ would be reduced into gaseousH2 before Mg reduction could occur. So, the direct electrolysis of moltenMgCl2 in the absence of water is required because the reduction potential to obtain Mg is lower than the stability domain of water on an Eh–pH diagram (Pourbaix diagram).
The production of metallic magnesium at thecathode (reduction reaction) is accompanied by the oxidation of the chloride anions at theanode with release of gaseouschlorine. This process is developed at a large industrial scale.
Magnesium chloride is one of many substances used for dust control,soil stabilization, andwind erosion mitigation.[12] When magnesium chloride is applied to roads and bare soil areas, both positive and negative performance issues occur which are related to many application factors.[13]
Ziegler-Natta catalysts, used commercially to producepolyolefins, often containMgCl2 as acatalyst support.[14] The introduction ofMgCl2 supports increases the activity of traditional catalysts and allowed the development of highly stereospecific catalysts for the production ofpolypropylene.[15]
Magnesium chloride is also aLewis acid catalyst inaldol reactions.[16]
Magnesium chloride is used for low-temperature de-icing ofhighways,sidewalks, andparking lots. When highways have dangerous ice buildup, road maintainers apply magnesium chloride to deter ice from bonding to the pavement, allowingsnow plows to clear treated roads more efficiently.
For the purpose of preventing ice from forming on pavement, magnesium chloride is applied in three ways: anti-icing, which involves spreading it on roads to prevent snow from sticking and forming; prewetting, which means a liquid formulation of magnesium chloride is sprayed directly onto salt as it is being spread onto roadway pavement, wetting the salt so that it sticks to the road; and pretreating, when magnesium chloride and salt are mixed together before they are loaded onto trucks and spread onto paved roads.Calcium chloride damages concrete twice as fast as magnesium chloride.[17] The amount of magnesium chloride is supposed to be controlled when it is used for de-icing as it may cause pollution to the environment.[18]
Magnesium chloride is used innutraceutical andpharmaceutical preparations. The hexahydrate is sometimes advertised as "magnesium oil". Magnesium Chloride is also anelectrolyte.
Magnesium chloride (E511[19]) is an importantcoagulant used in the preparation oftofu fromsoy milk.
In Japan it is sold asnigari (にがり, derived from the Japanese word for "bitter"), a white powder produced fromseawater after thesodium chloride has been removed, and the water evaporated. In China, it is calledlushui (卤水).
Nigari or Lushui is, in fact, natural magnesium chloride, meaning that it is not completely refined (it contains up to 5%magnesium sulfate and various minerals). The crystals originate from lakes in the Chinese province ofQinghai, to be then reworked in Japan.
Because magnesium is a mobile nutrient, magnesium chloride can be effectively used as a substitute formagnesium sulfate (Epsom salt) to help correct magnesium deficiency in plants viafoliar feeding. The recommended dose of magnesium chloride is smaller than the recommended dose of magnesium sulfate (20 g/L).[20] This is due primarily to the chlorine present in magnesium chloride, which can easily reach toxic levels if over-applied or applied too often.[21]
It has been found that higher concentrations of magnesium intomato and somepepper plants can make them more susceptible to disease caused by infection of the bacteriumXanthomonas campestris, since magnesium is essential for bacterial growth.[22]
It is used to supply the magnesium necessary to precipitate phosphorus in the form of struvite from agricultural waste[23] as well as human urine.
Magnesium concentrations in naturalseawater are between 1250 and 1350 mg/L, around 3.7% of the total seawater mineral content.Dead Sea minerals contain a significantly higher magnesium chloride ratio, 50.8%. Carbonates and calcium[clarification needed] are essential for all growth ofcorals,coralline algae,clams, andinvertebrates. Magnesium can be depleted bymangrove plants and the use of excessivelimewater or by going beyond natural calcium,alkalinity, andpH values.[24] The most common mineral form of magnesium chloride is its hexahydrate, bischofite.[25][26] Anhydrous compound occurs very rarely, as chloromagnesite.[26] Magnesium chloride-hydroxides, korshunovskite and nepskoeite, are also very rare.[27][28][26]
Magnesium ions are bitter-tasting, and magnesium chloride solutions are bitter in varying degrees, depending on the concentration.
Magnesium toxicity from magnesium salts is rare in healthy individuals with a normal diet, because excess magnesium is readily excreted inurine by thekidneys. A few cases oforal magnesium toxicity have been described in persons with normal renal function ingesting large amounts of magnesium salts, but it is rare. If a large amount of magnesium chloride is eaten, it will have effects similar tomagnesium sulfate, causing diarrhea, although the sulfate also contributes to the laxative effect in magnesium sulfate, so the effect from the chloride is not as severe.
Chloride (Cl−) and magnesium (Mg2+) are both essential nutrients important for normal plant growth. Too much of either nutrient may harm a plant, although foliar chloride concentrations are more strongly related with foliar damage than magnesium. High concentrations ofMgCl2 ions in the soil may be toxic or change water relationships such that the plant cannot easily accumulate water and nutrients. Once inside the plant, chloride moves through the water-conducting system and accumulates at the margins of leaves or needles, where dieback occurs first. Leaves are weakened or killed, which can lead to the death of the tree.[29]
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