Mohr's salt ; Ammonium iron(II) sulfate ; ammonium ferrous sulfate ; ammonium ferrous alum

Mohr’s Salt
Other Names: Ammonium iron(II) sulfate, Ammonium ferrous sulfate hexahydrate

Summary Formula: (NH₄)₂Fe(SO₄)₂·6H₂O
Molar Mass: 392.14 g/mol
CAS Number: 7783-85-9
EC Number: 233-151-8
Appearance: Light green crystalline powder

Mohr’s salt is a stable, double salt composed of ammonium sulfate and iron(II) sulfate, crystallized with six molecules of water. It is widely used in laboratories and industrial applications as a source of ferrous ions. Its stability against air oxidation makes it particularly suitable for analytical procedures.

Chemical and Physical Properties

Density: ~1.86 g/cm³
Melting Point: Decomposes upon heating (loses water)
Boiling Point: Not applicable (decomposes)
Solubility in Water: Highly soluble
Solubility in Other Solvents: Practically insoluble
Odor: Odorless

Applications

Analytical Chemistry: Used as a primary standard in redox titrations (e.g., permanganometry) due to its stability in air.

Pigment Preparation: Used in the synthesis of iron-based pigments.

Industrial Chemistry: Serves in wastewater treatment and as a reducing agent in chemical synthesis.

Education and Teaching: Commonly used in laboratory demonstrations of redox reactions.

Safety

Signal Word: Warning

Hazard Statements:

• H315: Causes skin irritation

• H319: Causes serious eye irritation

• H335: May cause respiratory irritation

Precautionary Statements:

• P261: Avoid breathing dust

• P280: Wear protective gloves, clothing, and eye protection

• P305+P351+P338: IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing

• P337+P313: If eye irritation persists: Get medical advice/attention

First Aid Measures

Eye Contact: Rinse cautiously with water for several minutes. Seek medical attention if irritation develops.
Skin Contact: Wash thoroughly with soap and water. Remove contaminated clothing.
Inhalation: Move to fresh air. Seek medical help if respiratory symptoms appear.
Ingestion: Rinse mouth with water. Do not induce vomiting. Seek medical attention if larger amounts are ingested.

Handling and Storage

Storage Conditions: Store in a tightly closed container in a cool, dry place. Protect from air and moisture to prevent oxidation.
Handling Precautions: Avoid generation and inhalation of dust. Use appropriate PPE during handling.