Metaphosphoric Acid | Glacial phosphoric acid

Metaphosphoric Acid
Other Names: Polymetaphosphoric acid, Glacial phosphoric acid
CAS Number: 37267-86-0
Sum Formula: (HPO₃)ₙ
Molar Mass: Variable (depends on polymerization degree)
Appearance: White, glassy or crystalline solid

Metaphosphoric acid is a polymeric form of phosphoric acid composed of repeating HPO₃ units. It exists as a glassy, hygroscopic solid and is used in analytical chemistry, metal treatment, and chemical synthesis. It acts as a strong dehydrating agent and a medium for specific precipitation reactions.

Chemical and Physical Properties
Density: ~2.2 g/cm³
Melting Point: Softens at ~80°C, decomposes upon strong heating
Boiling Point: Decomposes before boiling
Solubility in Water: Slowly hydrolyzes to orthophosphoric acid
Solubility in Organic Solvents: Practically insoluble
Odor: Odorless
Acidity (pKa): Strong acid
Stability: Hygroscopic, reacts with moisture

Applications
Used as a reagent in analytical chemistry (e.g., protein precipitation)
Applied in metal surface treatment and passivation
Intermediate in specialty phosphate compound production
Used in laboratory synthesis as a dehydration and condensation agent
Applied in non-aqueous titrations and separation techniques

Safety

Signal Word: Danger

First Aid Measures
Eye Contact: Rinse immediately with plenty of water for at least 15 minutes. Seek immediate medical attention
Skin Contact: Remove contaminated clothing. Rinse with water and wash thoroughly with soap
Inhalation: Move to fresh air. If symptoms occur, seek medical help
Ingestion: Rinse mouth with water. Do not induce vomiting. Seek urgent medical attention

Handling and Storage
Store in a tightly sealed container in a cool, dry, and well-ventilated area
Protect from moisture to prevent hydrolysis
Keep away from bases and reactive metals
Handle under fume hood with proper PPE