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| Magnesium chloride | |
|---|---|
| General | |
| Systematic name | Magnesium chloride |
| Molecular formula | MgCl2 (anhydrous) MgCl2.6H2O (hexahydrate) |
| Molar mass | 95.22 g/mol (anhydrous) 203.31 g/mol (hexahydrate) |
| Appearance | white or colourless crystalline solid |
| CAS number | (anhydrous) [7791-18-6 (hexahydrate) |
| Properties | |
| Density and phase | 2.32 g/cm3 (anhydrous solid) 1.56 g/cm3 (hexahydrate solid) |
| Solubility in water | 54.2 g/100 cm3 (20 °C) |
| Solubility in ethanol | 7.4 g/100 cm3 (30 °C) |
| Melting point | 714 °C (987 K) |
| Boiling point | 1412 °C (1685 K) |
| Structure | |
| Coordination geometry | (octahedral, 6-coordinate?) |
| Crystal structure | CdCl2 |
| Dipole moment | ? D |
| Hydrates | Hexahydrate |
| Hazards | |
| MSDS | Magnesium chloride MSDS |
| Main hazards | irritant |
| NFPA 704 | |
| Flash point | ?°C |
| R/S statement | R: ? S: ? |
| RTECS number | ? |
| Supplementary data page | |
| Structure and properties | n, εr, etc. |
| Thermodynamic data | Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Other anions | magnesium fluoride magnesium bromide magnesium iodide |
| Other cations | beryllium chloride calcium chloride |
| Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) Chemical infobox | |
Magnesium chloride is composed of magnesium and chlorine and is a typical ionic halide, being highly polar and soluble in water. It is a weak Lewis acid, so not surprisingly the hexahydrate can undergo partial hydrolysis when heated. Magnesium chloride can be extracted from brine or sea water, and is a commonly used source of magnesium metal, which can be extracted from MgCl2 using electrolysis. In 1990, US production was around one million tonnes, with a bulk price around $180 per tonne.
Chemical properties
Magnesium chloride can serve as a source of magnesium compounds, for example by precipitation:
MgCl2(aq) + Ca(OH)2(aq) → Mg(OH)2(s) + CaCl2(aq)
It can be electrolysed to give magnesium metal:
Both of these reactions are used in the Dow process for production of metallic magnesium.* Unlike aluminium chloride, hydrated MgCl2 can be dehydrated without hydrolysis (under certain conditions). This allows anhydrous MgCl2 to be used as a cheap source of the metal via electrolysis.
Magnesium chloride can also act as a weak Lewis acid, and salts containing the MgCl42- are known, though rare.*
Preparation
In the Dow process, magnesium chloride is regenerated from magnesium hydroxide using hydrochloric acid:
Mg(OH)2(s) + 2 HCl → MgCl2(aq) + 2 H2O(l)
It may also be prepared from magnesium carbonate by a similar reaction.
Uses
Magnesium chloride is used for a variety of applications, besides the manufacture of magnesium via the Dow process discussed above. It is used in the manufacture of textiles, paper, fireproofing agents, cements and refrigeration brine.*
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. Nigari consists mostly of magnesium chloride, with some magnesium sulfate and other trace elements.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. 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. The use of this product 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 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 to solid Magnesium chloride, forming Mg(NH3)6Cl2. Ammonia is released by mild heat, and is then passed through a catalyst to give hydrogen gas.
Precautions
Irritant. Wear gloves and goggles. For more details see a MSDS-sheet.
References
- Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.
- N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, 1984.
- Hill, Petrucci, McCreary, Perry, "General Chemistry", 4th ed., Pearson/Prentice Hall, Upper Saddle River, New Jersey, USA.
External links
Suppliers/Manufacturers
Chlorides | Magnesium compounds | Metal halides | Deliquescent substances
Magnesiumchlorid | Magnesiumchlorid | 塩化マグネシウム | Chlorek magnezu | Магнезијум хлорид
"Magnesium chloride"