Chemistry:Magnesium nitrate

Magnesium nitrate
Names
	IUPAC name Magnesium nitrate
	Other names Nitromagnesite (hexahydrate)
Identifiers
CAS Number	10377-60-3 ; 15750-45-5 (dihydrate) ; 13446-18-9 (hexahydrate) ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:64736 ;
ChemSpider	23415 ;
EC Number	233-826-7;
PubChem CID	25212;
RTECS number	OM3750000 (anhydrous); OM3756000 (hexahydrate);
UNII	77CBG3UN78 ; V85K20LJMK (hexahydrate) ;
UN number	1474
	InChI InChI=1S/Mg.2NO3/c;22-1(3)4/q+2;2-1 Key: YIXJRHPUWRPCBB-UHFFFAOYSA-N ; InChI=1/Mg.2NO3/c;22-1(3)4/q+2;2-1 Key: YIXJRHPUWRPCBB-UHFFFAOYAA;
	SMILES [N+](=O)([O-])[O-].[N+](=O)([O-])[O-].[Mg+2];
Properties
Chemical formula	Mg(NO3)2
Molar mass	148.32 g/mol (anhydrous); 184.35 g/mol (dihydrate); 256.41 g/mol (hexahydr.)
Appearance	White crystalline solid
Density	2.3 g/cm3 (anhydrous) ; 2.0256 g/cm3 (dihydrate) ; 1.464 g/cm3 (hexahydrate)
Melting point	129 °C (264 °F; 402 K) (dihydrate) ; 88.9 °C (hexahydrate)
Boiling point	330 °C (626 °F; 603 K) decomposes
Solubility in water	71 g/100 mL (25 °C)
Solubility	moderately soluble in ethanol, ammonia
Refractive index (nD)	1.34 (hexahydrate)
Structure
Crystal structure	cubic
Thermochemistry
Heat capacity (C)	141.9 J/mol K
Std molar; entropy (So298)	164 J/mol K
Std enthalpy of; formation (ΔfH⦵298)	-790.7 kJ/mol
Gibbs free energy (ΔfG˚)	-589.4 kJ/mol
Hazards
Main hazards	Irritant
Safety data sheet	External MSDS
GHS pictograms
GHS Signal word	Warning
GHS hazard statements	H272, H315, H319, H335
GHS precautionary statements	P210, P220, P221, P261, P264, P271, P280, P302+352, P304+340, P305+351+338, P312, P321, P332+313, P337+313, P362, P370+378, P403+233, P405, P501
NFPA 704 (fire diamond)	0 1 0 OX
Related compounds
Other anions	Magnesium sulfate; Magnesium chloride
Other cations	Beryllium nitrate; Calcium nitrate; Strontium nitrate; Barium nitrate
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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	Infobox references

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

↑ Lide, David R., ed (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. ISBN 0-8493-0487-3.
↑ ^2.0 ^2.1 Thiemann, Michael; Scheibler, Erich; Wiegand, Karl Wilhelm (2005). Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a17_293. ISBN 3-527-30673-0.
↑ Mindat, http://www.mindat.org/min-2920.html
↑ 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.