Citric acid
Citric acid is a weak organic acid. It can be found in citrus fruits. 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.
Citric acid | |
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[[Image: | |
2-Hydroxypropane-1,2,3-tricarboxylic acid | |
Identifiers | |
CAS number | |
PubChem | |
EC number | 201-069-1 |
DrugBank | DB04272 |
KEGG | D00037 |
ChEBI | CHEBI:30769 |
RTECS number | GE7350000 |
SMILES | OC(=O)CC(O)(C(=O)O)CC(=O)O |
Properties | |
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 | |
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] |
Structure | |
Crystal structure | Monoclinic |
Thermochemistry | |
Std enthalpy of formation ΔfH |
−1548.8 kJ/mol[2] |
Std enthalpy of combustion ΔcH |
−1960.6 kJ/mol[6] −1972.34 kJ/mol (monohydrate)[2] |
Standard molar entropy S |
252.1 J/(mol·K)[6] |
Specific heat capacity, C | 226.51 J/(mol·K) (26.85 °C)[6] |
Pharmacology | |
ATC code | |
Hazards | |
Main hazards | skin and eye irritant |
NFPA 704 |
|
Explosive limits | 8% |
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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
- As a water softener
- It is often used in detergents, to avoid the smell of acid, esp. Acetic acid
- As a preserving agent
- Citric acid and its salts prevent blood clotting. Blood donations are kept liquid using citric acid.
Citric Acid Media
Speciation diagram for a 10-millimolar solution of citric acid
Powdered citric acid being used to prepare lemon pepper seasoning
References
- ↑ CID 22230 from PubChem
- ↑ 2.0 2.1 2.2 2.3 2.4 CID 311 from PubChem
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Cite error: Invalid
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. - ↑ "Data for Biochemical Research". ZirChrom Separations, Inc. Retrieved January 11, 2012.
- ↑ "Ionization Constants of Organic Acids". Michigan State University. Retrieved January 11, 2012.
- ↑ 6.0 6.1 6.2 Citric acid in Linstrom, Peter J.; Mallard, William G. (eds.); NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg (MD), http://webbook.nist.gov (retrieved 2014-06-02)