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Formic acid

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Formic acid
Formic acid.svg
Formic acid 85 percent.jpg
Other names Carbonous acid; Formylic acid; Hydrogen carboxylic acid; Hydroxy(oxo)methane; Metacarbonoic acid; Oxocarbinic acid; Oxomethanol
CAS number 64-18-6
PubChem 284
EC number 200-579-1
DrugBank DB01942
KEGG C00058
RTECS number LQ4900000
Molecular formula CH2O2
Molar mass 46.01 g mol-1
Appearance Colorless fuming liquid
Odor Pungent, penetrating
Density 1.220 g/mL
Melting point

8.4 °C, 282 K, 47 °F

Boiling point

100.8 °C, 374 K, 213 °F

Solubility in water Miscible
Solubility Miscible with ether, acetone, ethyl acetate, glycerol, methanol, ethanol
Partially soluble in benzene, toluene, xylenes
log P −0.54
Vapor pressure 35 mmHg (20 °C)[2]
Acidity (pKa) 3.77[3]
-19.90·10−6 cm3/mol
Refractive index (nD) 1.3714 (20 °C)
Viscosity 1.57 cP at 268 °C
Molecular shape Planar
Dipole moment 1.41 D (gas)
Std enthalpy of
−425.0 kJ/mol
Std enthalpy of
−254.6 kJ/mol
Standard molar
131.8 J/mol K
ATC code
Main hazards Corrosive; irritant;
NFPA 704

NFPA 704.svg

R-phrases Template:R10 R35
S-phrases (S1/2) S23 S26 S45
Explosive limits 14–34%[source?]
18%–57% (90% solution)[2]
U.S. Permissible
exposure limit (PEL)
TWA 5 ppm (9 mg/m3)[2]
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Formic acid is named after the ants that use it for attack and defense

Formic acid, or methanoic acid, is the simplist carboxylic acid and has the chemical formula HCO2H. Many animals use for defence. The word "formic" comes from the Latin word for ant, formica, referring to its early isolation by the distillation of ant bodies, and the trivial name in some languages means "ant-acid", such as Dutch mierenzuur, Danish myresyre, Faroese meyrusýra, Français acide formique and German Ameisensäure. Esters, salts, and the anions derived from formic acid are called formates.

In the 15th century, many alchemists reported that ants use an acidid fluid for defense. English naturalist John Ray was the first to get formic acid, by distilling ants, in 1671.

In nature, it is found in most ants[4]. The wood ants from the genus Formica can spray formic acid on their preys or to defend the nest. It is also known from the trichomes of stinging nettle (Urtica dioica). Formic acid is a naturally occurring component of the atmosphere due primarily to forest emissions [5].


  1. 1.0 1.1 Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 745. doi:10.1039/9781849733069 . ISBN 978-0-85404-182-4 . 
  2. 2.0 2.1 2.2 "NIOSH Pocket Guide to Chemical Hazards #0296". National Institute for Occupational Safety and Health (NIOSH). 
  3. Brown, H. C. et al., in Braude, E. A. and Nachod, F. C., Determination of Organic Structures by Physical Methods, Academic Press, New York, 1955.
  4. Hoffman, Donald R. "Ant venoms" Current Opinion in Allergy and Clinical Immunology 2010, vol. 10, pages 342–346. doi:10.1097/ACI.0b013e328339f325
  5. Sanhueza, E., & Andreae, M. O. (1991). "Emission of formic and acetic acids from tropical savanna soils.". Geophysical Research Letters 18 (9): 1707-1710.