The short answer
Citric acid is a weak tribasic organic acid. Formula C6H8O7, anhydrous CAS 77-92-9, molecular weight 192.12 g/mol. It is a white crystalline solid, extremely soluble in water, and non-toxic at the levels used in food.
It is bought for three properties that rarely occur together: it is a food-safe acid with a clean, bright sourness; it is a strong chelator of calcium, magnesium and iron; and it is readily biodegradable. That combination is why it appears in a soft drink, a descaling liquid and a metal passivation bath alike.
Formula, molecular weight and identifiers
| Form | Formula | CAS | Molecular weight | Acid content |
|---|---|---|---|---|
| Anhydrous | C6H8O7 | 77-92-9 | 192.12 g/mol | 100 % |
| Monohydrate | C6H8O7·H2O | 5949-29-1 | 210.14 g/mol | 91.4 % |
IUPAC name: 2-hydroxypropane-1,2,3-tricarboxylic acid. Food additive number E330. HS code 2918.14; the citrate salts sit under 2918.15. Melting point of the anhydrous form is about 153 °C, density about 1.66 g/cm3, and solubility in water is very high — roughly 59 g per 100 mL at 20 °C and rising steeply with temperature.
Anhydrous versus monohydrate
The two forms are the same acid; the monohydrate simply carries one molecule of water in the crystal lattice. Which one you get out of a crystalliser is decided by temperature: below about 36.6 °C the monohydrate is the stable solid, above it the anhydrous.
Three things follow for a buyer:
- Dosing. The monohydrate is about 8.6 % water, so you need roughly 1.09 kg of it to replace 1 kg of anhydrous. Swapping one for the other without recalculating will shift your pH.
- Moisture sensitivity. In effervescent tablets, dry drink mixes and anhydrous powder blends, the monohydrate's water can start the acid–bicarbonate reaction in the pack. Those applications specify anhydrous.
- Caking and handling. The anhydrous form is slightly more hygroscopic in humid storage; the monohydrate is more stable on the shelf but loses water if warmed above the transition point. Both need a sealed, dry warehouse.
Three acid groups and what they do
Citric acid has three carboxylic acid groups, which ionise one after another with approximate pKa values of 3.13, 4.76 and 6.40. Those three closely spaced constants are what make it such a useful buffer: together with sodium citrate it holds pH steadily anywhere between roughly 3 and 6.5, which covers most of the food, beverage and topical cosmetic range.
The first dissociation is strong enough to give real acidity — a 1 % solution sits near pH 2.2 — while the acid itself remains weak, so it does not attack equipment or skin the way a mineral acid does. This is the reason a soft drink can be as acidic as pH 2.5 and still be drinkable.
Why citric acid chelates metals
Three carboxylate groups and a hydroxyl group on the same small molecule can wrap around a metal ion and hold it from several directions at once. Citrate binds calcium, magnesium, iron, copper and zinc in stable, water-soluble complexes.
That single property explains a long list of uses. It keeps hardness ions from precipitating soap in a detergent, which is why citrate is a standard phosphate-free builder. It holds iron in solution during metal cleaning instead of letting it redeposit as rust stain. It stops trace copper and iron catalysing fat oxidation in food, so it works as a synergist alongside antioxidants. And it is used to strip iron oxide from stainless steel and passivate the surface, a far gentler alternative to nitric acid.
How citric acid is made
Essentially all commercial citric acid comes from submerged fermentation. A carbohydrate feedstock — cane molasses, corn starch hydrolysate or cassava starch — is fermented with Aspergillus niger, which excretes citric acid into the broth. The acid is then recovered, historically by precipitation as calcium citrate and re-acidification, increasingly by solvent extraction or ion exchange, and finally crystallised to the anhydrous or monohydrate form.
Two practical consequences. The residual impurity profile — oxalate, sulphate, residual solvent, colour — depends on the recovery route, not on the assay, so those limits belong in your specification. And because the feedstock can be corn or cassava starch, buyers with a non-GMO, allergen or Halal or Kosher requirement should ask about the substrate and get the declaration in writing.
Commercial grades and particle size
| Grade | Typical assay | What is controlled |
|---|---|---|
| Technical | 99.5 %+ | Assay, moisture, sulphated ash, colour |
| Food (E330 / FCC) | 99.5 to 100.5 % | Oxalate, sulphate, heavy metals, readily carbonisable substances, residual solvent |
| Pharmacopoeial (IP / BP / USP / EP) | Per monograph | Full monograph including identification, related substances, bacterial endotoxins where applicable |
| Analytical reagent | 99.5 %+ | Full trace-element profile |
Particle size is specified separately and matters more than people expect. Fine grades dissolve fast and suit liquids and instant powders; granular grades resist caking, dose accurately by volume and segregate less in a dry blend; and a direct-compression tablet formulation will call for a defined mesh range rather than any convenient powder.
Scapex Exports supplies citric acid anhydrous food grade, citric acid monohydrate, pharma grade, technical grade and detergent grade.
What citric acid is used for
- Food and beverage. The dominant use. Acidulant and flavour enhancer in soft drinks, juices, confectionery, jams and canned goods; pH control for pectin gels; and an antioxidant synergist that ties up the trace metals which would otherwise catalyse rancidity.
- Household cleaning. Descaler for kettles, boilers, coffee machines and washing machines; phosphate-free builder in laundry and dishwash formulations; and the acid in many bathroom and limescale products.
- Pharmaceutical. The acid half of effervescent tablets and granules, a pH adjuster in syrups and injectables, and an anticoagulant as sodium citrate in blood collection.
- Metal treatment. Descaling and passivation of stainless steel, and boiler and heat exchanger cleaning, where its chelating power keeps dissolved iron from re-plating on the surface.
- Cosmetics. pH adjustment in creams, shampoos and serums, and a mild exfoliant as an alpha hydroxy acid.
- Textiles and construction. pH control in dyeing and finishing, and a set retarder in cement and gypsum systems.
Handling, packing and export documents
- Hazard. Not classified as a dangerous good for transport. It is a skin and serious eye irritant as a dust or concentrated solution, so goggles, gloves and dust extraction are appropriate.
- Materials. Solutions attack carbon steel and, given time, will dull galvanised surfaces. Use stainless steel, HDPE, polypropylene, FRP or lined equipment.
- Segregation. Keep away from strong oxidisers and from alkalis and carbonates, which react vigorously and generate carbon dioxide.
- Storage. Cool and dry, off the floor, bags sealed. Both forms cake if they take up moisture; the anhydrous form is the more sensitive of the two.
- Packing. 25 kg paper or PP bags with an inner liner, and 1000 to 1250 kg jumbo bags. Food and pharma grades take a food-contact liner.
An export consignment should carry a certificate of analysis stating assay, water, sulphated ash, oxalate, sulphate, chloride, heavy metals, colour and particle size distribution; a 16-section GHS safety data sheet; commercial invoice and packing list; certificate of origin; and for food and pharmacopoeial grades the E330, FCC or monograph reference with any Halal, Kosher, non-GMO or allergen declarations the destination requires.
Enquire with a specification
Citric acid anhydrous and monohydrate are supplied by Scapex Exports as a manufacturer and supplier from qualified Indian producers, in technical, food, pharmacopoeial and analytical grades, in the mesh range your process needs, with certificate of analysis, safety data sheet and full export documentation.
Send the form, grade, assay, particle size, packing and destination port, along with any Halal, Kosher or non-GMO requirement, and you will get a quotation written against that specification rather than a generic one.
Frequently asked questions
What is the formula of citric acid?
C6H8O7. The anhydrous form has CAS number 77-92-9 and a molecular weight of 192.12 g/mol. The monohydrate, C6H8O7 H2O, has CAS 5949-29-1 and a molecular weight of 210.14 g/mol. Structurally it is 2-hydroxypropane-1,2,3-tricarboxylic acid: three carboxylic acid groups and one hydroxyl group on a three-carbon backbone.
What is the difference between anhydrous and monohydrate citric acid?
One molecule of water of crystallisation. The monohydrate contains about 8.6 % water by mass, so on an acid basis one kilogram of monohydrate delivers about 914 g of citric acid. Which one crystallises depends on temperature: below about 36.6 degrees C you get the monohydrate, above it the anhydrous. Anhydrous is preferred wherever moisture would harm the formulation, as in effervescent tablets and dry beverage mixes.
Is citric acid the same as E330?
Yes. E330 is the European food additive number for citric acid. The same material may also be specified against the Food Chemicals Codex, the European Pharmacopoeia, the United States Pharmacopeia or the Indian Pharmacopoeia, which set tighter limits on oxalate, sulphate, heavy metals and residual solvents than a technical grade would.
Is citric acid made from citrus fruit?
Almost none of it is, despite the name. Commercial citric acid is produced by submerged fermentation of a carbohydrate feedstock such as molasses, corn starch or cassava starch using the mould Aspergillus niger, then recovered and crystallised. Citrus extraction was displaced commercially in the first half of the twentieth century because fermentation is far cheaper.
Why is citric acid used as a descaler and cleaner?
Because it does two jobs at once. It is acidic enough to dissolve carbonate scale, and it chelates calcium, magnesium and iron, binding them in solution so they do not redeposit. It is also biodegradable and far less aggressive to skin and metal than mineral acids, which is why it has displaced them in consumer descalers and in phosphate-free detergent builders.
What is citric acid?
Citric Acid Anhydrous (CAS 77-92-9) is supplied as a white crystalline powder, with the molecular formula C6H8O7 and a molecular weight of 192.12 g/mol. Its main applications include food acidulant, beverages and cleaning agents. Scapex Exports exports and supplies it from India in ≥99.5% Food Grade, with a batch Certificate of Analysis (COA) and MSDS.
What is citric acid used for?
The main applications of Citric Acid Anhydrous are food acidulant, beverages and cleaning agents.
Is citric acid soluble in water?
Our product data gives the solubility of Citric Acid Anhydrous as: in water, 3.83 × 10⁵ mg/L at 25 °C.