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 | |
|---|---|
 |
 |
| [[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 |
1
2
0
|
| 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
Lemons, oranges, limes, and other citrus fruits contain high concentrations of citric acid.
Speciation diagram for a 10-millimolar solution of citric acid
Powdered citric acid being used to prepare lemon pepper seasoning
Structure of an iron(III) citrate complex
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
<ref>tag; no text was provided for refs namedchemister. - ↑ "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)