(NH+4)2[Fe(H2O)6]2+[SO42−]2 | |
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| Names | |
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| IUPAC name Ammonium iron(II) sulfate | |
| Other names Ferrous ammonium sulfate Ammonium iron sulfate Mohr's salt | |
| Identifiers | |
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3D model (JSmol) | |
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| ChemSpider | |
| ECHA InfoCard | 100.030.125 |
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| Properties | |
| Fe(SO4)(NH4)2(SO4) (anhydrous) Fe(SO4)(NH4)2(SO4)·6H2O (hexahydrate) | |
| Molar mass | 284.05 g mol−1 (anhydrous) 392.14 g mol−1 (hexahydrate) |
| Appearance | Blue-green solid |
| Density | 1.86 g/cm3 |
| Melting point | 100 to 110 °C (212 to 230 °F; 373 to 383 K) |
| Boiling point | Not applicable |
| 269 g/L (hexahydrate) | |
| Hazards | |
| GHS labelling: | |
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| Warning | |
| H315,H319,H335 | |
| P261,P264,P271,P280,P302+P352,P304+P340,P305+P351+P338,P312,P321,P332+P313,P337+P313,P362,P403+P233,P405,P501 | |
| NFPA 704 (fire diamond) | |
| Safety data sheet (SDS) | Fisher MSDS |
| Related compounds | |
Related compounds | Ammonium iron(III) sulfate |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Ammonium iron(II) sulfate, orMohr's salt, is theinorganic compound with the formula(NH4)2SO4·Fe(SO4)·6H2O. Containing two differentcations, Fe2+ andNH+4, it is classified as adouble salt offerrous sulfate andammonium sulfate. It is a common laboratory reagent because it is readily crystallized, and crystals resist oxidation by air. Like the other ferrous sulfate salts, ferrous ammonium sulfate dissolves in water to give theaquo complex [Fe(H2O)6]2+, which hasoctahedral molecular geometry.[1] Its mineral form ismohrite.
This compound is a member of a group of double sulfates called Schönites orTutton's salts. Tutton's salts form monoclinic crystals and have formula M2N(SO4)2·6H2O (M = various monocations). With regards to the bonding, crystals consist ofoctahedra [Fe(H2O)6]2+ centers, which are hydrogen bonded to sulfate and ammonium.[2]
Mohr's salt is named after the German chemistKarl Friedrich Mohr, who made many important advances in the methodology of titration in the 19th century.
Inanalytical chemistry, this salt is the preferred source of ferrous ions as the solid has a long shelf life, being resistant to oxidation. This stability extends somewhat to solutions reflecting the effect of pH on the ferrous–ferric redox couple. This oxidation occurs more readily at high pH. The ammonium ions make solutions of Mohr's salt slightly acidic, which slows this oxidation process.[1][3] Sulfuric acid is commonly added to solutions to reduce oxidation to ferric iron.
It is used inGel dosimetry to measure high doses of gamma rays.[4]
Mohr's salt forms upon evaporation of an equimolar mixture of aqueousferrous sulfate andammonium sulfate.[5]
Common impurities includemagnesium,nickel,manganese,lead, andzinc, many of which form isomorphoussalts.[6]
