Magnesium nitrate

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Magnesium nitrate
Magnesium nitrate hexahydrate fertilizer sample.jpg
Magnesium nitrate fertilizer on a watchglass
Names
IUPAC name
Magnesium nitrate
Other names
Magnesium dinitrate
Nitric acid, magnesium salt
Nitromagnesite
Properties
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
Odor Odorless
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
Hazards
Safety data sheet Sigma-Aldrich (hexahydrate)
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
5,440 mg/kg (rat, oral)
Related compounds
Related compounds
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).
Infobox references

Magnesium nitrate is a hygroscopic magnesium salt, with the formula Mg(NO3)2, widely used as fertilizer.

Properties

Chemical

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.

Physical

Magnesium nitrate is a hygroscopic white solid, which readily dissolves in water.

Availability

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 it's difficult, as it tends to decompose at high temperatures.

Lastly, it can be purchased from chemical suppliers.

Preparation

Can be prepared by mixing magnesium sulfate, aka Epsom salt with calcium nitrate.

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.

Adding nitric acid to magnesium oxide, hydroxide or carbonate will give magnesium nitrate.

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.

Projects

Handling

Safety

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.

Storage

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.

Disposal

No special disposal is required, can be safely used as fertilizer.

References

Relevant Sciencemadness threads