Citric acid (IUPAC name 2-hydroxypropane-1,2,3-tricarboxylic acid) is a weak organic acid, mostly used in the food industry, where it serves as a preservative and a food additive that gives a pleasant sour taste. It has the chemical formula C6H8O7.
Citric acid will react in solution with bases, carbonates and bicarbonates. It will also react with magnesium. As can be seen with its use as a preservative for fruits, it often serves as a reducing agent, similar to ascorbic acid, both in nature and some syntheses.
Citric acid is at standard conditions a white hygroscopic crystalline powder. It exists either in an anhydrous (water-free) form or as a monohydrate. The monohydrate can be converted to the anhydrous form by heating above 78 °C. It is soluble in water, ethanol, diethyl ether, ethyl acetate, DMSO and insoluble in benzene, toluene, chloroform, carbon disulfide.
Citric acid is available in stores as lemon salt, either pure or mixed with other additives. It can be found in pickling and canning sections of grocery stores already in pure, food-grade form.
Williams-Sonoma sells citric acid in small glass jars.
Citric acid can be prepared by reacting a citrate salt with a stronger acid.
Industrially it is extracted from Aspergillus niger cultures. However, because it's dirt cheap, citric acid is easier to buy than to make it yourself.
- Alka-Seltzer rocket
- Anthocyanin extraction
- HMTD synthesis
- Propane-1,2,3-tricarboxylic acid synthesis
Being a weak acid, it is not very toxic, but in high concentrations can irritate the skin and sensitive tissues. Ingesting large quantities of citric acid will upset the stomach and cause digestive problems, as well as metabolic acidosis.
Solid citric acid should be stored in closed bottles, in a dry place.
Storage of citrate-containing solutions often promotes the growth of bacteria that may metabolize it. Adding an antibacterial can prevents this.
Citric acid can be neutralized before disposal, though this is not always necessary. It can be poured down the drain or dumped in the ground.