Citric acid was first isolated in 1784 by the chemist Carl Wilhelm Scheele, who crystallized it from lemon juice. It can exist either in an anhydrous (water-free) form or as a monohydrate. The anhydrous form crystallizes from hot water, while the monohydrate forms when citric acid is crystallized from cold water. The monohydrate can be converted to the anhydrous form at about 78 °C. Citric acid also dissolves in absolute (anhydrous) ethanol (76 parts of citric acid per 100 parts of ethanol) at 15 °C. It decomposes with loss of carbon dioxide above about 175 °C.
Monohydrate citric acid has one water molecule as part of it’s chemical formula, and exists as a white powder. Citrate or citric acid is often used to adjust pH, to add sour flavor to foods and beverages, and to form the salt derivative of minerals and metals for pharmaceuticals, as in the case of potassium citrate, a dietary supplement.
|Molar mass||192.12 g·mol−1|
|Appearance||crystalline white solid|
|Density||1.542 g/cm3 (18 °C, monohydrate)|
|Melting point||156 °C (313 °F; 429 K)|
|Boiling point||310 °C (590 °F; 583 K) decomposes from 175 °C
|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)
|Solubility||soluble in alcohol, ether, ethyl acetate, DMSO
insoluble in C6H6, CHCl3, CS2, toluene
|Viscosity||6.5 cP (50% aq. sol.)|