Chemical compound

Magnesium nitrate refers to inorganic compounds with the formula Mg(NO3)2(H2O)x, where x = 6, 2, and 0. All are white solids.[2] The anhydrous material is hygroscopic, quickly forming the hexahydrate upon standing in air. All of the salts are very soluble in both water and ethanol.

Occurrence, preparation, structure

Being highly water soluble, magnesium nitrate occurs naturally only in mines and caverns as nitromagnesite (hexahydrate form).[3]

The magnesium nitrate used in commerce is made by the reaction of nitric acid and various magnesium salts.

Structure of [Mg(H2O)6]2+ in the dinitrate salt.[4]

Use

The principal use is as a dehydrating agent in the preparation of concentrated nitric acid.[2]

Its fertilizer grade has 10.5% nitrogen and 9.4% magnesium, so it is listed as 10.5-0-0 + 9.4% Mg. Fertilizer blends containing magnesium nitrate also have ammonium nitrate, calcium nitrate, potassium nitrate and micronutrients in most cases; these blends are used in the greenhouse and hydroponics trade.

Reactions

Magnesium nitrate reacts with alkali metal hydroxide to form the corresponding nitrate:

Mg(NO3)2 + 2 NaOH → Mg(OH)2 + 2 NaNO3.

Since magnesium nitrate has a high affinity for water, heating the hexahydrate does not result in the dehydration of the salt, but rather its decomposition into magnesium oxide, oxygen, and nitrogen oxides:

2 Mg(NO3)2 → 2 MgO + 4 NO2 + O2.

The absorption of these nitrogen oxides in water is one possible route to synthesize nitric acid. Although inefficient, this method does not require the use of any strong acid.

It is also occasionally used as a desiccant.

References

  1. ^ Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. ISBN 0-8493-0487-3.
  2. ^ a b Thiemann, Michael; Scheibler, Erich and Wiegand, Karl Wilhelm (2005). "Nitric Acid, Nitrous Acid, and Nitrogen Oxides". Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a17_293. ISBN 3527306730.{{cite encyclopedia}}: CS1 maint: uses authors parameter (link)
  3. ^ Mindat, http://www.mindat.org/min-2920.html
  4. ^ Schefer, J.; Grube, M. (1995). "Low temperature structure of magnesium nitrate hexahydrate, Mg (N O3)2 . 6(H2 O): a neutron diffraction study at 173 K". Materials Research Bulletin. 30: 1235–1241. doi:10.1016/0025-5408(95)00122-0.{{cite journal}}: CS1 maint: uses authors parameter (link)