Fluorophosphoric acid

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Fluorophosphoric acid
Structure of fluorophosphonic acid
IUPAC name
Fluorophosphonic acid[1]
Other names
  • Fluorophosphoric acid[1]
  • Monoluorophosphoric acid[1]
  • Phosphorofluoridic acid[1]
3D model (JSmol)
ECHA InfoCard 100.202.790 Edit this at Wikidata
EC Number
  • 233-433-0
  • InChI=1S/FH2O3P/c1-5(2,3)4/h(H2,2,3,4)
  • OP(=O)(O)F
Molar mass 99.985 g·mol−1
Appearance Colorless liquid[1]
Odor Practically odorless[1]
Density 1.818 g/cm3[1]
Melting point −78 °C (−108 °F; 195 K)[1]
Boiling point Decomposes
Occupational safety and health (OHS/OSH):
Main hazards
Causes skin burns and eye damage.
GHS labelling:
GHS05: CorrosiveGHS06: Toxic
H301, H311, H314, H330
P260, P264, P270, P271, P280, P284, P301+P310, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P310, P312, P320, P321, P322, P330, P361, P363, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Fluorophosphoric acid is the inorganic compound with the formula H2PO3F. It is a colorless viscous liquid that solidifies to a rigid glass upon cooling at −78 °C (−108 °F).[2][1]


Fluorophosphoric acid is produced commercially by treating phosphorus pentoxide with hydrogen fluoride. A less pure product can also be prepared by hydrolysis of phosphorus oxyfluoride, a reaction that first produces difluorophosphoric acid:[2]

POF3 + H2O → HPO2F2 + HF

The next steps give monofluorophosphoric acid:

HPO2F2 + H2O → H2PO3F + HF


Fluorophosphoric acid is a dibasic acid, with pKa1 of 5.5 and pKa2 of around 8.5.[1] The conjugate bases are the monofluorophosphates, which are hydrolytically robust. When fluorophosphoric acid is diluted with water, it hydrolyzes, producing phosphoric acid. Fluorophosphoric acid is not flammable.[1]


Fluorophosphoric acid is used to make protective coatings on metal surfaces, as a metal cleaner and as an electrolytic or chemical polishing agent. The sodium salt of this acid, sodium monofluorophosphate, is the most used dentifrice additive for the reduction of tooth decay.[1]


Fluorophosphoric acid is corrosive to living tissue. It can cause severe skin burns and permanent eye damage. Ingestion can cause severe burns and permanent damage to gastrointestinal system. Inhalation of this acid may cause severe burns to respiratory system and chemical pneumonia. Inhalation, ingestion or contact with skin with this acid may cause severe injury or death. Symptoms from contact or inhalation may be delayed.[1]


  1. ^ a b c d e f g h i j k l m https://pubchem.ncbi.nlm.nih.gov/compound/Fluorophosphoric-acid
  2. ^ a b Charles B. Lindahl, Tariq Mahmood (2000). "Fluorine Compounds, Inorganic, Phosphorus". Kirk‐Othmer Encyclopedia of Chemical Technology. doi:10.1002/0471238961.1608151912091404.a01. ISBN 9780471484943.{{cite encyclopedia}}: CS1 maint: uses authors parameter (link)