Molar Mass of Citric Acid (C₆H₈O₇)
Learn how chemists calculate the molar mass of Citric Acid (C₆H₈O₇), with a clear formula breakdown, worked steps, and study notes · IUPAC name: 2-Hydroxypropane-1,2,3-tricarboxylic acid.
Quick answer
The molar mass of Citric Acid (C₆H₈O₇) is
192.123g/mol
One mole of Citric Acid therefore has a mass of 192.123 grams—the value you use for stoichiometry and laboratory preparation.
Reviewed for educational accuracy · Accuracy policy
- CAS Registry Number
- 77-92-9
- PubChem CID
- 311
- SMILES
- C(C(=O)O)C(CC(=O)O)(C(=O)O)O
Step-by-step calculation
Let's find the molar mass of Citric Acid (C₆H₈O₇) together—step by step, as if you are seeing the formula for the first time.
Step 1 — Look at the chemical formula
The formula is C₆H₈O₇. Each letter stands for an element. The little number after a letter (the subscript) tells you how many atoms of that element are in one molecule or formula unit.
- 6 Carbon atoms (C)
- 8 Hydrogen atoms (H)
- 7 Oxygen atoms (O)
Step 2 — Look up each atomic mass
Atomic mass comes from the periodic table. It is the average mass of one mole of atoms of that element, in grams per mole (g/mol). Think of it as the "price tag" for one mole of that element.
- Carbon (C) = 12.011 g/mol
- Hydrogen (H) = 1.008 g/mol
- Oxygen (O) = 15.999 g/mol
Step 3 — Multiply atoms × atomic mass
Why multiply? If one oxygen atom "costs" about 16 g/mol, then two oxygen atoms cost twice as much. Each element's contribution is: number of atoms × atomic mass.
- 6 × 12.011 = 72.066 g/mol (Carbon)
- 8 × 1.008 = 8.064 g/mol (Hydrogen)
- 7 × 15.999 = 111.993 g/mol (Oxygen)
Step 4 — Add the contributions
Why add? The molar mass of the whole compound is simply the total mass of every atom in the formula. Add each element's contribution:
72.066 + 8.064 + 111.993 = 192.123 g/mol
Step 5 — Final answer
Molar mass of Citric Acid = 192.123 g/mol
That means one mole of Citric Acid (C₆H₈O₇) has a mass of about 192.12 grams.
Quick summary
Read the formula → count atoms → look up atomic masses → multiply → add → report g/mol. For C₆H₈O₇, the total is 192.123 g/mol.
Common beginner mistakes
- Treating citric acid as monoprotic — it has three dissociable protons with distinct pKa values.
- Confusing citric acid (from citrus/fermentation) with ascorbic acid (vitamin C) — both are food acids but structurally and metabolically distinct.
- Assuming all citric acid is fruit-derived — the vast majority sold commercially is produced by fungal fermentation.
Memory trick
Draw the three carboxyl groups and central hydroxyl to remember why citric acid is triprotic and a strong chelator.
Mini practice
Without looking above, list the atoms in C₆H₈O₇ and write one multiplication line for the heaviest element. Then check your work against Step 3.
Real-world example
If a recipe asks for 0.100 mol of Citric Acid, mass needed = 0.100 × 192.123 = 19.212 g. That is how chemists turn a mole amount into a weighable sample.
Atomic contribution table
Each row shows how much mass one element contributes to the total for C₆H₈O₇.
| Element | Atoms | Atomic mass | Contribution | Mass % |
|---|---|---|---|---|
| C | 6 | 12.011 | 72.066 g/mol | 37.5% |
| H | 8 | 1.008 | 8.064 g/mol | 4.2% |
| O | 7 | 15.999 | 111.993 g/mol | 58.3% |
| Total molar mass | 192.123 g/mol | 100% | ||
Mass contribution chart
Count every atom in this formula, multiply by atomic mass, then add. That total is the molar mass used in lab weighing.
Download study sheets
Save a printable summary, revision sheet, practice worksheet, or laboratory reference for Citric Acid (C₆H₈O₇).
Practice this calculation
Without looking above, write the atom count for C₆H₈O₇, then compute the molar mass. Check your answer against 192.123 g/mol.
Next challenge: how many grams are in 0.250 mol of Citric Acid? Multiply 0.250 × 192.123 to get 48.031 g.
Physical and chemical properties
Physical properties
| Appearance | White crystalline powder or colorless crystals |
| Color | White to colorless |
| Odor | Odorless |
| State (STP) | Solid |
| Density | 1.665 g/cm³ (anhydrous) |
| Melting point | 153–154 °C (anhydrous) |
| Boiling point | Decomposes above 175 °C |
| Solubility | 1,330 g/L water at 20 °C (highly soluble) |
| Crystal structure | Monoclinic (anhydrous and monohydrate forms) |
Chemical properties
| Classification | Weak triprotic carboxylic acid / hydroxy tricarboxylic acid |
| Family | Tricarboxylic acids / hydroxy acids |
| Acidity | Weak triprotic (pKa₁ = 3.13, pKa₂ = 4.76, pKa₃ = 6.40) |
| Polarity | Highly polar (multiple hydrogen-bonding groups) |
| Geometry | Trigonal planar at each carboxyl carbon; tetrahedral at central carbon |
| Oxidation states | Variable across carbons; central carbon bears –OH substituent |
Applications
Industrial uses
- Food and beverage acidulant (E330) in soft drinks, candies, and jams
- Metal cleaning and descaling agents (chelation of calcium and iron scale)
- Cosmetic and personal care pH adjustment and preservation
- Biodegradable chelating agent replacing phosphates in some detergents
Laboratory uses
- Citrate buffer preparation across a wide pH range (pH 3–7)
- Anticoagulant in blood collection tubes (calcium chelation)
- Metal ion masking agent in titrations and complexometric analysis
- Model compound for triprotic acid dissociation and titration curves
Central intermediate of the citric acid (Krebs/TCA) cycle in aerobic respiration; naturally abundant in citrus fruits and involved in bone mineral regulation.
Preparation and production
Industrially produced by submerged fermentation of sugar substrates (corn starch, molasses, or sucrose syrup) with Aspergillus niger under controlled trace-metal and nitrogen-limited conditions that favor citrate overproduction. Laboratory-grade material is purified by crystallization from the fermentation broth after removing biomass and impurities.
Global citric acid production exceeds 2 million tonnes annually, almost entirely via fermentation; China is the dominant producer, supplying the majority of world demand for food, beverage, and industrial-grade material.
Important reactions of Citric Acid
C₆H₈O₇ + 3 NaOH → Na₃C₆H₅O₇ + 3 H₂O
- Reaction type
- Acid–base neutralization (complete, triprotic)
- Conditions
- Excess strong base
- Explanation
- All three carboxyl protons are neutralized to form trisodium citrate; partial neutralization gives mono- or disodium citrate salts at lower base ratios.
- Products
- Trisodium citrate and water
- Why it matters
- Citrate salt production, buffer and food additive manufacture
Related ideas: Triprotic acids · Multiple equivalence points · Salt formation
C₆H₈O₇ + 3 NaHCO₃ → Na₃C₆H₅O₇ + 3 H₂O + 3 CO₂
- Reaction type
- Acid–carbonate (effervescence)
- Conditions
- Aqueous, room temperature
- Explanation
- Citric acid reacts with sodium bicarbonate to release carbon dioxide gas, the basis of effervescent tablets and fizzing drink powders.
- Products
- Trisodium citrate, water, and carbon dioxide gas
- Why it matters
- Effervescent tablet formulation, food and pharmaceutical products
Related ideas: Gas evolution · Acid–base reactions · Formulation chemistry
Acetyl-CoA + Oxaloacetate + H₂O → Citrate + CoA-SH
- Reaction type
- Enzymatic condensation (citrate synthase, biochemical)
- Conditions
- Mitochondrial matrix, aqueous, enzyme-catalyzed
- Explanation
- Citrate synthase catalyzes the condensation of a two-carbon acetyl unit with four-carbon oxaloacetate to form six-carbon citrate, the entry step of the Krebs cycle.
- Products
- Citrate and free coenzyme A
- Why it matters
- Cellular respiration, metabolic biochemistry
Related ideas: Krebs cycle · Enzyme catalysis · Cellular metabolism
C₆H₈O₇ + 3 Fe³⁺ → [Fe(C₆H₅O₇)]-type chelate complexes
- Reaction type
- Metal chelation (complex ion formation)
- Conditions
- Aqueous, varies with pH
- Explanation
- Deprotonated citrate carboxylate groups coordinate metal cations such as Fe³⁺ and Ca²⁺, forming soluble chelate complexes that resist precipitation and catalytic side reactions.
- Products
- Soluble metal–citrate chelate complexes
- Why it matters
- Food preservation, anticoagulant blood tubes, descaling formulations
Related ideas: Chelation · Complex ions · Coordination chemistry
History and discovery
Carl Wilhelm Scheele first isolated citric acid from lemon juice in 1784. Industrial production shifted from citrus extraction to microbial fermentation after James Currie discovered in 1917 that Aspergillus niger mold could excrete large quantities of citric acid from sugar, a process Pfizer commercialized in 1919 and which remains the dominant production method today. Hans Krebs elucidated the citric acid cycle's central metabolic role in 1937, earning the 1953 Nobel Prize in Physiology or Medicine.
Carl Wilhelm Scheele, 1784 — isolated citric acid crystals from lemon juice.
Interesting facts
- Lemons and limes owe their sour taste largely to citric acid, which can make up 5–8% of their juice by weight.
- The citric acid cycle processes roughly two-thirds of the calories in a typical diet, making citrate one of biochemistry's most central small molecules.
- Aspergillus niger fermentation, first commercialized in 1919, produces more citric acid worldwide each year than could ever be practically extracted from citrus fruit.
- Citric acid's chelating power is strong enough that it is used to safely descale coffee makers and kettles without harsh mineral acids.
Comparison with similar compounds
Citric acid (192.12 g/mol, triprotic) is structurally and functionally distinct from ascorbic acid/vitamin C (176.12 g/mol) despite both being common 'sour' food acids — citric acid is a tricarboxylic Krebs cycle intermediate, while ascorbic acid is a lactone with antioxidant vitamin activity.
Storage, handling, and safety
Store the anhydrous or monohydrate crystalline solid in a dry, sealed container — citric acid is mildly hygroscopic and the monohydrate can lose or gain water depending on humidity. Stable at room temperature away from strong oxidizers.
Low hazard; mild irritant to eyes and broken skin at high concentrations. Use standard laboratory gloves and eye protection when handling concentrated solutions or powder to avoid dust irritation.
Generally recognized as safe for food use; concentrated solid or solutions may mildly irritate eyes, skin, and respiratory tract.
- Mild eye and skin irritation from concentrated powder or solution
- Respiratory irritation from inhaled dust
- Dental enamel erosion with excessive, prolonged exposure (as with other food acids)
Classification: Not classified as hazardous under GHS for food-grade material at typical exposure levels
Exam notes and student tips
Exam notes
- Molar mass C₆H₈O₇ = 6(12.01) + 8(1.008) + 7(16.00) = 192.12 g/mol.
- Triprotic acid: pKa₁ = 3.13, pKa₂ = 4.76, pKa₃ = 6.40.
- Citrate synthase catalyzes the entry step of the Krebs cycle: acetyl-CoA + oxaloacetate → citrate.
- Effervescent reaction: C₆H₈O₇ + 3 NaHCO₃ → Na₃C₆H₅O₇ + 3 H₂O + 3 CO₂.
Student tips
- Draw the three carboxyl groups and central hydroxyl to remember why citric acid is triprotic and a strong chelator.
- Link citrate directly to the Krebs cycle diagram — it's the first stable product after acetyl-CoA enters.
- For titration curve questions, expect three distinct buffering regions and equivalence points spanning pH 3–7.
Common mistakes
- Treating citric acid as monoprotic — it has three dissociable protons with distinct pKa values.
- Confusing citric acid (from citrus/fermentation) with ascorbic acid (vitamin C) — both are food acids but structurally and metabolically distinct.
- Assuming all citric acid is fruit-derived — the vast majority sold commercially is produced by fungal fermentation.
Misconceptions
- Citric acid is not 'weak' in the sense of being harmless in all forms — concentrated solid can still irritate skin and eyes.
- The Krebs cycle is not identical to citric acid itself — citrate is one key intermediate in a multi-step enzymatic cycle.
- Citric acid is not primarily extracted from lemons commercially — fermentation of sugar substrates dominates production.
Practice questions
1. Calculate the molar mass of citric acid (C₆H₈O₇).
Show answer
6(12.01) + 8(1.008) + 7(16.00) = 192.12 g/mol
2. How many grams of citric acid are needed to prepare 500 mL of 0.100 M solution?
Show answer
0.100 mol/L × 0.500 L = 0.0500 mol; 0.0500 × 192.12 = 9.61 g
3. How many moles of NaOH are required to fully neutralize 19.2 g of citric acid?
Show answer
19.2 g ÷ 192.12 g/mol = 0.100 mol citric acid; requires 3 × 0.100 = 0.300 mol NaOH (triprotic)
4. Which functional groups make citric acid an effective metal chelator?
Show answer
Its three carboxylate groups (and central hydroxyl) can simultaneously coordinate a metal cation, forming a stable ring-like chelate complex.
Frequently asked questions about Citric Acid
192.12 g/mol for anhydrous C₆H₈O₇.
Chemistry of Citric Acid
The sections above give the number you need for calculations. Here we look more closely at how Citric Acid (C₆H₈O₇) behaves chemically—so the molar mass connects to real reactions, properties, and laboratory practice.
Citric acid (C₆H₈O₇) is a triprotic organic acid with molar mass 192.12 g/mol (C 6 × 12.01 + H 8 × 1.008 + O 7 × 16.00), built around a central carbon bearing a hydroxyl group and three carboxylic acid arms. It occurs naturally in citrus fruits — lemons contain roughly 5–8% citric acid by weight — and is one of the most widely produced organic acids in the world, manufactured almost entirely today by fermenting sugar (usually from corn starch or molasses) with the mold Aspergillus niger rather than extracting it from fruit.
Citric acid's central importance in biochemistry comes from its role as the namesake of the citric acid cycle (also called the Krebs cycle or TCA cycle), the hub of aerobic metabolism where acetyl-CoA from carbohydrates, fats, and proteins is oxidized to release energy captured as NADH, FADH₂, and GTP, ultimately powering the electron transport chain and ATP synthesis in nearly all aerobic organisms. Citrate itself is the first stable intermediate formed in the cycle, condensing with oxaloacetate before undergoing a sequence of oxidative decarboxylations back to oxaloacetate.
As a food and industrial acidulant, citric acid provides the tart, refreshing sourness in soft drinks, candies, and jams (E330 on ingredient labels), while its three ionizable carboxyl groups and hydroxyl oxygen make it an excellent metal chelator — it binds calcium, iron, and other metal ions tightly, which underlies its use in food preservation (sequestering trace metal catalysts that promote oxidative spoilage), water softening, metal cleaning formulations, and even as an anticoagulant additive in blood collection tubes, where it chelates the calcium ions required for clotting.
C₆H₈O₇ contains three carboxyl groups (–COOH) and one hydroxyl group (–OH) attached to a central three-carbon backbone. Each carboxyl proton can dissociate stepwise (pKa₁ = 3.13, pKa₂ = 4.76, pKa₃ = 6.40), making citric acid triprotic, and the fully deprotonated citrate³⁻ ion is an excellent multidentate ligand for metal cations because its three carboxylate oxygens (and sometimes the hydroxyl) can coordinate simultaneously.
Citric acid behaves as a weak triprotic Brønsted acid, neutralizing bases stepwise to form mono-, di-, and tricitrate salts. Its chelating carboxylate groups bind di- and trivalent metal cations (Ca²⁺, Fe³⁺, Mg²⁺) strongly, forming soluble complexes that prevent metal-catalyzed oxidation and precipitation. It reacts with bicarbonate to release CO₂ (the fizz in effervescent tablets combining citric acid with sodium bicarbonate) and esterifies with alcohols at any of its three carboxyl groups.
Citrate as the entry point of the Krebs cycle
The citric acid cycle takes its name from citrate, the six-carbon molecule formed when acetyl-CoA condenses with oxaloacetate via citrate synthase. From there, citrate is isomerized and oxidatively decarboxylated through isocitrate, α-ketoglutarate, and succinate back to oxaloacetate, generating the reduced electron carriers (NADH, FADH₂) that feed the electron transport chain — making citric acid's chemistry a direct link between organic acid structure and cellular respiration.
Industrial fermentation over fruit extraction
Although citric acid was first isolated from lemon juice by Carl Wilhelm Scheele in 1784, essentially all commercial citric acid today is produced by fermenting sugar substrates (corn starch, molasses, or sucrose) with the mold Aspergillus niger, which excretes citric acid in large quantities under carefully controlled low-manganese, high-sugar conditions — a striking example of microbial fermentation displacing natural extraction for a compound most people associate with citrus fruit.
Metal chelation and its practical consequences
Citric acid's three carboxylate groups can wrap around metal cations to form stable, water-soluble chelate complexes. This property is exploited in food preservation (sequestering trace iron and copper that catalyze oxidative rancidity), descaling and metal-cleaning products (dissolving mineral scale by complexing calcium and magnesium), and anticoagulant blood-collection tubes, where citrate binds the calcium ions essential for the clotting cascade.
Stepwise triprotic dissociation and buffering
With three distinct pKa values (3.13, 4.76, 6.40) spanning roughly pH 3 to 7, citric acid and its conjugate citrate bases form an unusually versatile buffer system spanning a wide physiological and food-relevant pH range, which is why citrate–phosphate and citrate-only buffers are common choices in biochemistry labs and pharmaceutical formulations.
Effervescence chemistry in tablets and drink powders
Combining citric acid with sodium bicarbonate in a dry mixture produces the fizzing reaction of effervescent tablets and drink powders only once water is added: the acid protonates bicarbonate to carbonic acid, which decomposes to CO₂ gas and water, giving the characteristic bubbling and tangy taste of products like effervescent vitamin C tablets.
Recalculate any formula with the molar mass calculator, compare atoms on the periodic table, or browse more compounds in the organic library.
References and further reading
- PubChem CID 311: Citric acid compound data
- NIST Chemistry WebBook: Thermodynamic properties
- IUBMB: Citric acid (Krebs/TCA) cycle biochemistry