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.
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:
MgCl2(l) → Mg(l) + Cl2(g)
Both of these reactions are used in the Dow process for production of metallic magnesium.[3]
Magnesium chloride can also act as a weak Lewis acid, and salts containing the MgCl42- are known, though rare.[2]
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.[3]
Magnesium chloride is also the foremost soy milk coagulant for the preparation of tofu.
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.
Precautions
Irritant. Wear gloves and goggles. For more details see a Baker MSDS.
Suppliers/Manufacturers
Aldrich: http://www.sigmaaldrich.com Alfa: http://www.alfa.com/alf/index.htm VWR: http://www.vwr.com/index.htm or Fisher: https://www1.fishersci.com/index.jsp
External links
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.
