Magnesium nitrate fertilizer on a watchglass
| IUPAC name
| Other names
Nitric acid, magnesium salt
| Mg(NO3)2 (anhydrous)|
Mg(NO3)2·2 H2O (dihydrate)
Mg(NO3)2·6 H2O (hexahydrate)
|Molar mass|| 148.32 g/mol (anhydrous)|
184.35 g/mol (dihydrate)
256.41 g/mol (hexahydrate)
|Appearance||White hygroscopic 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 (192.0 °F; 362.0 K) (hexahydrate)
|Boiling point||330 °C (626 °F; 603 K) (decomposition)|
| 42 g/100 ml (20 °C)|
71.2 g/100 ml (25 °C)
|Solubility||Soluble in ethanol|
|Vapor pressure||0.494 mmHg at 25 °C|
|Safety data sheet||Sigma-Aldrich (hexahydrate)|
|Lethal dose or concentration (LD, LC):|
LD50 (Median dose)
|5,440 mg/kg (rat, oral)|
| Calcium nitrate|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Magnesium nitrate is a hygroscopic magnesium salt, with the formula Mg(NO3)2, widely used as fertilizer.
Heating magnesium nitrate will cause it to lose water, but it's extremely difficult to convert it into anhydrous form, as it decomposes to release nitrogen oxides, leaving behind magnesium oxide.
- 2 Mg(NO3)2 → 2 MgO + 4 NO2 + O2.
Magnesium nitrate is a hygroscopic white solid, which readily dissolves in water.
Magnesium nitrate is sold in many gardening stores as magnesium and nitrogen fertilizer (11-0-0 0-9.6), which is the hexahydrated form, and it's fairly pure. Magnesium nitrate is also found in other magnesium fertilizers, where it's mixed with other compounds. Purification is required to obtain this compound, though removing the water is difficult, as the salt tends to decompose at high temperatures.
Lastly, it can be purchased from chemical suppliers.
- MgSO4 + Ca(NO3)2 → Mg(NO3)2 + CaSO4
Filter off the insoluble calcium sulfate from the mixture to obtain a solution of Mg(NO3)2. To dry it, you will have to heat it gently on a water bath and then cool the concentrated solution. Use a seed crystal to obtain crystals of this compound and remove the excess water using vacuum.
Anhydrous magnesium nitrate can be obtained by boiling the hydrated form in concentrated nitric acid, though this route has not been confirmed. Passing nitrogen dioxide through heated magnesium oxide at 100 °C should give magnesium nitrate anhydrous and nitric oxide. Another route would be to mix anhydrous calcium or barium nitrate dissolved in anhydrous methanol or ethanol, with anhydrous magnesium sulfate.
- Make nitrogen dioxide and nitric acid
- Anhydrous magnesium nitrate can be used to increase the concentration of nitric acid past its azeotrope
Because of its hygroscopicity, magnesium nitrate cannot sustain an energetic mixture like potassium nitrate can, making it useful as a safe nitrate ion source. Skin contact with the anhydrous compound should be avoided as it can be irritating.
Magnesium nitrate should be kept in closed bottles, to prevent it from absorbing water from air and hardening.
Anhydrous Mg(NO3)2 should be kept in air-tight containers, or in a desiccator.
No special disposal is required, can be safely used as fertilizer.