Citric acid

Citric acid
IUPAC name	2-hydroxypropane-1,2,3-tricarboxylic acid
Other names	3-carboxy-3-hydroxypentanedioic acid
Identifiers
CAS number	77-92-9
PubChem	311
DrugBank	DB04272
KEGG	D00037
ChEBI	CHEBI:30769
SMILES	C(C(=O)O)C(CC(=O)O)(C(=O)O)O
InChI InChI=1/C6H8O7/c7-3(8)1-6(13,5(11)12)2-4(9)10/h13H,1-2H2,(H,7,8)(H,9,10)(H,11,12)
Properties
Molecular formula	C6H8O7
Molar mass	192.124 g/mol (anhydrous) 210.14 g/mol (monohydrate)
Appearance	crystalline white solid
Density	1.665 g/cm3(1.5g/cm3 for monohydrate)
Melting point	153 °C, 426 K, 307 °F
Boiling point	175 °C, 448 K, 347 °F (decomposes)
Solubility in water	73 g/100 ml (20 °C)
Acidity (pKa)	pKa1 = 3.09 pKa2 = 4.75 pKa3 = 5.41
Hazards
Main hazards	skin and eye irritant
Related compounds
Related compounds	sodium citrate, calcium citrate
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 acts like a preservative. 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

• 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.

Other websites

• Citric acid analysis - free spreadsheet for titration of acids and pH calculation