Iron(II) nitrate is the nitrate salt of iron(II). It is commonly encountered as the green hexahydrate, Fe(NO3)2·6H2O, which is a metal aquo complex, however it is not commercially available unlike iron(III) nitrate due to its instability to air. The salt is soluble in water serves as a ready source of ferrous ions.
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| Properties | |
| Fe(NO3)2 | |
| Molar mass | 179.86 g/mol |
| Appearance | Green crystals (hexahydrate) |
| Melting point | 60 °C (140 °F; 333 K)[2] (hexahydrate) |
| Boiling point | 61 °C (142 °F; 334 K)[1] (decomposes) |
| 87.525 g/100 mL | |
| Structure | |
| Orthorhombic[3] | |
| Thermochemistry | |
Std enthalpy of formation (ΔfH⦵298) | -497.9 kJ/mol[1] |
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LD50 (median dose) | 428 mg/kg (subcutaneous, rabbit)[4] |
| Related compounds | |
Other anions | Iron(II) phosphate |
Other cations | Manganese(II) nitrate Cobalt(II) nitrate |
Related compounds | Iron(III) nitrate |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
Structure
No structure of any salt Fe(NO3)2·xH2O has been determined by X-ray crystallography. Nonetheless, the nature of the aquo complex [Fe(H2O)6]2+ is well known and relatively insensitive to the anion. The Fe-O distances are longer for [Fe(H2O)6]2+ (2.13 Å) than for the ferric analogue [Fe(H2O)6]3+ (1.99 Å).[5] Both [Fe(H2O)6]n+ complexes are high spin, which results in pale colors, paramagnetism, and weak Fe-O bonds.
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Production
Iron(II) nitrate can be produced in multiple ways, such as the reaction of iron metal with cold dilute nitric acid:
- 3 Fe + 8 HNO3 + 12 H2O → 3 Fe(NO3)2(H2O)6 + 2 NO
If this reaction is conducted below -10 °C, nonahydrate is produced. It readily releases water to give the hexahydrate.[1]
The above reaction can also co-produce ferric nitrate. Reacting iron(II) sulfate and lead nitrate under dilute ethanol and then evaporating the solution leads to the formation of the green crystals of the hexahydrate. A solution of iron(II) nitrate is produced by the ion-exchange reaction of iron(II) sulfate and barium nitrate, producing a concentration of up to 1.5 M due to the limited solubility of barium nitrate.[1][6][7]
The solution of the iron(II) nitrate-hydrazine complex is produced by the reaction of hydrazine nitrate and ferric nitrate at 40 °C with copper(II) nitrate as a catalyst:[8]
- 4 Fe(NO3)3 + N2H5NO3 → 4 Fe(NO3)2 + N2 + 4 HNO3
If the compound is used in situ, the compound is produced by the reaction of iron(II) chloride and calcium nitrate:[9][10]
- FeCl2 + Ca(NO3)2 → Fe(NO3)2 + CaCl2
Reactions
The hexahydrate melts at 60 °C and then decomposes at 61 °C into iron(III) oxide rather than iron(II) oxide.[1] A solution of iron(II) nitrate is much more stable, decomposing at 107 °C to iron(III), with the presence of nitric acid lowering the decomposition temperature. Concentrated nitric acid oxidizes iron(II) nitrate into iron(III) nitrate:[6]
- 3 Fe(NO3)2 + 4 HNO3 → 3 Fe(NO3)3 + NO + 2 H2O
Uses
Iron(II) nitrate has no uses, however, there is a potential use for dye removal.[10][9]