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Citric acid

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Citric acid
Zitronensäure - Citric acid.svg
Zitronensäure Kristallzucht.jpg
CAS number 77-92-9
PubChem 311
EC number 201-069-1
DrugBank DB04272
KEGG D00037
RTECS number GE7350000
Molecular formula C6H8O7
Molar mass 192.09 g mol-1
Appearance Crystalline white solid
Odor Odorless
Density 1.665 g/cm3 (anhydrous)
1.542 g/cm3 (18 °C, monohydrate)
Melting point

156 °C, 429 K, 313 °F

Boiling point

310 °C, 583 K, 590 °F

Solubility in water 117.43 g/100 mL (10 °C)
147.76 g/100 mL (20 °C)
180.89 g/100 mL (30 °C)
220.19 g/100 mL (40 °C)
382.48 g/100 mL (80 °C)
547.79 g/100 mL (100 °C)[2]
Solubility soluble in acetone, alcohol, ether, ethyl acetate, DMSO
insoluble in C6H6, CHCl3, CS2, toluene[3]
Solubility in ethanol 62 g/100 g (25 °C)[3]
Solubility in amyl acetate 4.41 g/100 g (25 °C)[3]
Solubility in diethyl ether 1.05 g/100 g (25 °C)[3]
Solubility in 1,4-Dioxane 35.9 g/100 g (25 °C)[3]
log P −1.64
Acidity (pKa) pKa1 = 3.13
pKa2 = 4.76
pKa3 = 6.39,[4] 6.40[5]
Refractive index (nD) 1.493–1.509 (20 °C)[2]
1.46 (150 °C)[3]
Viscosity 6.5 cP (50% aq. sol.)[2]
Crystal structure Monoclinic
Std enthalpy of
−1548.8 kJ/mol[2]
Std enthalpy of
−1960.6 kJ/mol[6]
−1972.34 kJ/mol (monohydrate)[2]
Standard molar
252.1 J/(mol·K)[6]
Specific heat capacity, C 226.51 J/(mol·K) (26.85 °C)[6]
ATC code
Main hazards skin and eye irritant
NFPA 704

NFPA 704.svg

Explosive limits 8%
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Citric acid crystals, magnified about 200 times, seen through a polarizing filter.

Citric acid is a weak organic acid. It can be found in citrus fruits ( like oranges). It is used by organisms for Krebs cycle. It acts like a preservative when added to food. It is also used to add a sour (acidic) taste to foods and soft drinks. In the European Union it is known as E 330, as a food additive.

Carl Wilhelm Scheele was the first who could extract citric acid from lemons, in 1782. The substance was probably known to alchemists, perhaps with a different name. The Arabian alchemist Geber is said to have discovered citric acid in the 9th century. Citric Acid contains 6 Carbon atoms, 8 Hydrogen atoms and 7 Oxygen atoms. Its chemical formula is C6H8O7.

Main uses


  1. CID 22230 from PubChem
  2. 2.0 2.1 2.2 2.3 2.4 CID 311 from PubChem
  3. 3.0 3.1 3.2 3.3 3.4 3.5 Cite error: Invalid <ref> tag; no text was provided for refs named chemister.
  4. "Data for Biochemical Research". ZirChrom Separations, Inc. Retrieved January 11, 2012. 
  5. "Ionization Constants of Organic Acids". Michigan State University. Retrieved January 11, 2012. 
  6. 6.0 6.1 6.2 Template:Nist

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