Ammonium iron(II) sulfate

Ammonium iron(II) sulfate

Names

IUPAC name
Ammonium iron(II) sulfate

Other names
Ferrous ammonium sulfate
Ammonium iron sulfate
Mohr\’s salt

Identifiers

CAS Number

anhydrous: 10045-89-3 checkYhexahydrate: 7783-85-9

3D model (JSmol)

Interactive image

ChEBI

anhydrous: CHEBI:76243hexahydrate: CHEBI:76181 checkY

ChemSpider

anhydrous: 23246 checkYhexahydrate: 13084980 checkY

ECHA InfoCard

100.030.125 Edit this at Wikidata

EC Number

233-151-8

PubChem CID

anhydrous: 24863hexahydrate: 15942308

UNII

anhydrous: 9Q764AYJ9G checkYhexahydrate: 99A04ICQ3J

CompTox Dashboard (EPA)

DTXSID4041028 Edit this at Wikidata

InChI
InChI=1S/Fe.2H3N.2H2O4S/c;;;2*1-5(2,3)4/h;2*1H3;2*(H2,1,2,3,4)/q+2;;;;/p-2 checkYKey: IMBKASBLAKCLEM-UHFFFAOYSA-L checkYInChI=1/Fe.2H3N.2H2O4S/c;;;2*1-5(2,3)4/h;2*1H3;2*(H2,1,2,3,4)/q+2;;;;/p-2Key: IMBKASBLAKCLEM-NUQVWONBAX

SMILES
.S(=O)(=O).S()(=O)=O..

Properties

Chemical formula

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

Solubility in water

269 g/L (hexahydrate)

Hazards

GHS labelling:

Pictograms

GHS07: Exclamation mark

Signal word

Warning

Hazard statements

H315, H319, H335

Precautionary statements

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)

NFPA 704 four-colored diamond

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Safety data sheet (SDS)

Fisher MSDS

Related compounds

Related compounds

Ammonium iron(III) sulfate

Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa).
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Infobox references

Chemical compound

Ammonium iron(II) sulfate, or Mohr\’s salt, is the inorganic compound with the formula (NH4)2Fe(SO4)2(H2O)6. Containing two different cations, Fe2+ and NH+4, it is classified as a double salt of ferrous sulfate and ammonium 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 the aquo complex 2+, which has octahedral molecular geometry. Its mineral form is mohrite.

Structure of ferrous ammonium sulfate with hydrogen bonding network highlighted (N is violet, O is red; S is orange, Fe = large red).

Mohr\’s salt is named after the German chemist Karl Friedrich Mohr, who made many important advances in the methodology of titration in the 19th century.

Applications

In analytical 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. Sulfuric acid is commonly added to solutions to reduce oxidation to ferric iron.

It is used in the Fricke\’s dosimeter to measure high doses of gamma rays.

Preparation

Mohr\’s salt is prepared by dissolving an equimolar mixture of hydrated ferrous sulfate and ammonium sulfate in water containing a little sulfuric acid, and then subjecting the resulting solution to crystallization. Ferrous ammonium sulfate forms light green crystals. This salt, when heated, ionises to give all cations and anions present in it.

Contaminants

Common impurities include magnesium, nickel, manganese, lead, and zinc, many of which form isomorphous salts.

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