Magnesium chloride hexahydrate is the magnesium salt of the hydrochloric acid, HCl. Its molecular formula is Cl2H12MgO6 or MgCl2(H2O)6 and its molar mass is 203.3 grams per mole. It is highly soluble in water. Its density is 1.569 grams per cubic centimeter, compared to 2.32 for the anhydrous form, and its melting point is 117 degrees Celsius compared to 714 degrees for the anhydrous compound.
Magnesium chloride hexahydrate is usually extracted from sea water or brine. The anhydrous form is obtained from ancient seabeds or from the evaporation of seawater due to sunlight. Magnesium chloride can also be obtained from the reaction of magnesium hydroxide, Mg(OH)2, with hydrochloric acid. The anhydrous substance is largely used in the industry to produce magnesium metal through the process of electrolysis.
Magnesium chloride has a range of other practical uses, including as a component of fire extinguishers and skin care products. It's also used in the processes of dust and erosion control, soil stabilization, and controlling ice during winter storms, as well as for hydrogen storage and as a nutritional supplement. It is used as a plant nutrient in agriculture, but high levels of magnesium promote bacterial growth, which makes plants such as tomatoes and peppers more vulnerable to disease. Magnesium chloride is also used as a coagulating agent in the production of tofu from soy milk.