Skip to Content

Phosphoric acid

**Production and Purification:**
– Phosphoric acid is produced through wet or dry processes.
– Wet process involves treating phosphate-containing minerals with sulfuric acid.
– Dry process involves reducing phosphate ore with coke in an electric arc furnace.
– Thermal process produces high-concentration phosphoric acid.
– Purification methods include liquid-liquid extraction and nanofiltration.
– Nanofiltration reduces impurities like cadmium and aluminum.
– Fractional crystallization produces high-purity phosphoric acid.
– Static crystallizers are used in the fractional crystallization process.

**Properties and Acidic Properties:**
– Phosphoric acid behaves as a triprotic acid in aqueous solution.
– Aqueous solutions exhibit freezing-point depression.
– Concentrated phosphoric acid may resist crystallization.
– Phosphoric acid can undergo self-condensation.
– pH adjustments yield monohydrogen phosphate or dihydrogen phosphate.
– Different pH values determine the type of phosphate salts formed.

**Industrial Uses:**
– Dominant use is in fertilizers, consuming approximately 90% of production.
– Used as a food and beverage acidifier and preservative.
– Contributes to the tangy taste in colas and jams.
– Soft drinks containing phosphoric acid can cause dental erosion.
– Potential to contribute to kidney stone formation, especially in excessive consumption.

**Safety Concerns:**
– Phosphoric acid can cause skin irritation at moderate concentrations.
– Concentrated solutions can lead to severe skin burns and permanent eye damage.
– Long-term regular cola intake linked to osteoporosis in women.
– Safety data sheets list phosphoric acid as immediately dangerous to life or health at certain concentrations.
– Colas associated with low bone mineral density in older women.

**Additional Information:**
– Safety information related to phosphoric acid can be found in the NIOSH Pocket Guide to Chemical Hazards.
– Various studies and articles provide data on the density, solubilities, and vapor pressure of phosphoric acid solutions.
– Books and publications cover topics such as purification, uses, and technology of phosphoric acid.
– Industry sources provide information on production, purification, and additives of phosphoric acid.
– Guidelines on dietary and pharmacologic management to prevent health issues related to phosphoric acid consumption are available.

Related Articles:
Phosphoric acid (Wikipedia)
This article is about orthophosphoric acid. For other acids commonly called "phosphoric acid", see Phosphoric acids and phosphates.
Not to be confused with Phosphorous acid.

Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula H3PO4. It is commonly encountered as an 85% aqueous solution, which is a colourless, odourless, and non-volatile syrupy liquid. It is a major industrial chemical, being a component of many fertilizers.

Phosphoric acid
Structural formula of phosphoric acid, showing dimensions
Ball-and-stick model
Ball-and-stick model
Space-filling model
Space-filling model
Names
IUPAC name
Phosphoric acid
Other names
Orthophosphoric acid
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.028.758 Edit this at Wikidata
EC Number
  • 231-633-2
E number E338 (antioxidants, ...)
KEGG
RTECS number
  • TB6300000
UNII
UN number 1805
  • InChI=1S/H3O4P/c1-5(2,3)4/h(H3,1,2,3,4) checkY
    Key: NBIIXXVUZAFLBC-UHFFFAOYSA-N checkY
  • InChI=1/H3O4P/c1-5(2,3)4/h(H3,1,2,3,4)
    Key: NBIIXXVUZAFLBC-UHFFFAOYAI
  • OP(=O)(O)O
Properties
H3PO4
Molar mass 97.994 g·mol−1
Appearance Colorless solid
Odor Odorless
Density 1.6845 g/cm3 (25 °C, 85%), 1.834 g/cm3 (solid)
Melting point 42.35 °C (108.23 °F; 315.50 K) anhydrous
29.32 °C (84.78 °F; 302.47 K) hemihydrate
Boiling point
  • 212 °C (414 °F)(only water evaporates)
  • 392.2 g/(100 g) (−16.3 °C)
  • 369.4 g/(100 mL) (0.5 °C)
  • 446 g/(100 mL) (15 °C)
  • 548 g/(100 mL) (20 °C)
Solubility Soluble in ethanol
log P −2.15
Vapor pressure 0.03 mmHg (20 °C)
Conjugate base Dihydrogen phosphate
−43.8·10−6 cm3/mol
  • 1.3420 (8.8% w/w aq. soln.)
  • 1.4320 (85% aq. soln) 25 °C
Viscosity 2.4–9.4 cP (85% aq. soln.)
147 cP (100%)
Structure
Monoclinic
Tetrahedral
Thermochemistry
145.0 J/(mol⋅K)
150.8 J/(mol⋅K)
−1271.7 kJ/mol
−1123.6 kJ/mol
Hazards
GHS labelling:
GHS05: Corrosive
Danger
H290, H314
P280, P305+P351+P338, P310
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
3
0
0
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
1530 mg/kg (rat, oral)
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 1 mg/m3
REL (Recommended)
 TWA 1 mg/m3 ST 3 mg/m3
IDLH (Immediate danger)
 1000 mg/m3
Safety data sheet (SDS) ICSC 1008
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

The compound is an acid. Removal of all three H+ ions gives the phosphate ion PO3−4. Removal of one or two protons gives dihydrogen phosphate ion H2PO−4, and the hydrogen phosphate ion HPO2−4, respectively. Phosphoric acid forms esters, called organophosphates.

The name "orthophosphoric acid" can be used to distinguish this specific acid from other "phosphoric acids", such as pyrophosphoric acid. Nevertheless, the term "phosphoric acid" often means this specific compound; and that is the current IUPAC nomenclature.