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Citric acid
Zitronensäure - Citric acid.svg
IUPAC name 2-hydroxypropane-1,2,3-tricarboxylic acid
Other names 3-carboxy-3-hydroxypentanedioic acid
CAS number 77-92-9
PubChem 311
DrugBank DB04272
KEGG D00037
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
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 is a weak organic acid. It occurs naturally in citrus fruits. 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.

Industrial-scale citric acid production first began in 1890 based on the Italian citrus fruit industry. More than a million tons of citric acid are manufactured every year.

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.

Natural occurrence and industrial production

Citric acid exists in greater than trace amounts in a variety of fruits and vegetables, most notably citrus fruits. Lemons and limes have particularly high concentrations of the acid; it can constitute as much as 8% of the dry weight of these fruits.


Food and drink

Powdered citric acid being used to prepare lemon pepper seasoning

Because it is one of the stronger edible acids, the dominant use of citric acid is used as a flavoring and preservative in food and beverages, especially soft drinks.

Citric acid can be added to ice cream as an emulsifying agent to keep fats from separating, to caramel to prevent sucrose crystallization, or in recipes in place of fresh lemon juice. Citric acid is used with sodium bicarbonate in a wide range of effervescent formulae, both for ingestion (e.g., powders and tablets) and for personal care (e.g., bath salts, bath bombs, and cleaning of grease).

Cleaning and chelating agent

Citric acid crystals, magnified about 200 times, seen through a polarizing filter.

Citric acid is an excellent chelating agent, binding metals by making them soluble. It is used to remove and discourage the buildup of limescale from boilers and evaporators. It can be used to treat water, which makes it useful in improving the effectiveness of soaps and laundry detergents. By chelating the metals in hard water, it lets these cleaners produce foam and work better without need for water softening. Citric acid is the active ingredient in some bathroom and kitchen cleaning solutions. A solution with a six percent concentration of citric acid will remove hard water stains from glass without scrubbing. In industry, it is used to dissolve rust from steel. Citric acid can be used in shampoo to wash out wax and coloring from the hair.


Lemons, oranges, limes, and other citrus fruits possess high concentrations of citric acid

Although a weak acid, exposure to pure citric acid can cause adverse effects. Inhalation may cause cough, shortness of breath, or sore throat. Over-ingestion may cause abdominal pain and sore throat. Exposure of concentrated solutions to skin and eyes can cause redness and pain. Long-term or repeated consumption may cause erosion of tooth enamel.

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See also

Kids robot.svg In Spanish: Ácido cítrico para niños

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