M

Mohr's Salt

FeSO₄·(NH₄)₂SO₄·6H₂O; M = 392.14 g/mol; double salt
Quick Reference
Formula / NotationFeSO₄·(NH₄)₂SO₄·6H₂O; M = 392.14 g/mol; double salt
Also Known AsAmmonium iron(II) sulfate hexahydrate, ferrous ammonium sulfate, Mohr salt

What is Mohr's Salt?

Ammonium iron(II) sulfate hexahydrate, (NH₄)₂Fe(SO₄)₂·6H₂O. It is a primary standard in volumetric analysis because it is stable in air (iron(II) in this salt is resistant to oxidation). Named after the German chemist Karl Friedrich Mohr.

Formula & Notation

FeSO₄·(NH₄)₂SO₄·6H₂O; M = 392.14 g/mol; double salt

Other Names / Synonyms: Ammonium iron(II) sulfate hexahydrate, ferrous ammonium sulfate, Mohr salt

Properties & Characteristics

Mohr's salt (ammonium iron(II) sulfate hexahydrate) is a pale green crystalline double salt of the formula FeSO₄·(NH₄)₂SO₄·6H₂O. It is a more stable source of Fe²⁺ than ferrous sulfate alone (resistant to aerial oxidation due to the slightly acidic solution formed on dissolution). It dissolves in water to give Fe²⁺, NH₄⁺, and SO₄²⁻ ions. It is a primary standard in redox titrimetry.

Uses & Applications

Mohr's salt is used as a primary standard in permanganate and dichromate titrations, as a source of standard Fe²⁺ solutions in analytical chemistry, as a reducing agent, in preparing dilute iron solutions for biological experiments, and as a reference material in colorimetry.

Safety Information

Mohr's salt is of low acute toxicity. Iron(II) compounds are mildly irritating to skin, eyes, and mucous membranes. Ingestion of large amounts can cause iron poisoning. The compound slowly oxidises in air to Fe³⁺ (turns brown/yellow) — use fresh preparations for primary standardisation.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Mohr's Salt
Formula FeSO₄·(NH₄)₂SO₄·6H₂O; M = 392.14 g/mol; double salt
Synonyms Ammonium iron(II) sulfate hexahydrate, ferrous ammonium sulfate, Mohr salt

Frequently Asked Questions

Ammonium iron(II) sulfate hexahydrate, (NH₄)₂Fe(SO₄)₂·6H₂O. It is a primary standard in volumetric analysis because it is stable in air (iron(II) in this salt is resistant to oxidation). Named after the German chemist Karl Friedrich Mohr.

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