Molar Mass of Acetic Acid (C₂H₄O₂)
Learn how chemists calculate the molar mass of Acetic Acid (C₂H₄O₂), with a clear formula breakdown, worked steps, and study notes · IUPAC name: Ethanoic acid.
Quick answer
The molar mass of Acetic Acid (C₂H₄O₂) is
60.052g/mol
One mole of Acetic Acid therefore has a mass of 60.052 grams—the value you use for stoichiometry and laboratory preparation.
Reviewed for educational accuracy · Accuracy policy
- CAS Registry Number
- 64-19-7
- PubChem CID
- 176
- SMILES
- CC(=O)O
Step-by-step calculation
Let's find the molar mass of Acetic Acid (C₂H₄O₂) 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 C₂H₄O₂. 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.
- 2 Carbon atoms (C)
- 4 Hydrogen atoms (H)
- 2 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.
- 2 × 12.011 = 24.022 g/mol (Carbon)
- 4 × 1.008 = 4.032 g/mol (Hydrogen)
- 2 × 15.999 = 31.998 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:
24.022 + 4.032 + 31.998 = 60.052 g/mol
Step 5 — Final answer
Molar mass of Acetic Acid = 60.052 g/mol
That means one mole of Acetic Acid (C₂H₄O₂) has a mass of about 60.05 grams.
Quick summary
Read the formula → count atoms → look up atomic masses → multiply → add → report g/mol. For C₂H₄O₂, the total is 60.052 g/mol.
Common beginner mistakes
- Treating acetic acid as strong acid — it is weak (partial dissociation).
- Confusing with ethanoic acid naming (same compound, IUPAC vs. common).
- Using C₂H₄O₂ without clarifying isomer (could theoretically be methyl formate).
Memory trick
Write CH₃COOH to identify carboxylic acid in isomer problems.
Mini practice
Without looking above, list the atoms in C₂H₄O₂ 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 Acetic Acid, mass needed = 0.100 × 60.052 = 6.005 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 C₂H₄O₂.
| Element | Atoms | Atomic mass | Contribution | Mass % |
|---|---|---|---|---|
| C | 2 | 12.011 | 24.022 g/mol | 40.0% |
| H | 4 | 1.008 | 4.032 g/mol | 6.7% |
| O | 2 | 15.999 | 31.998 g/mol | 53.3% |
| Total molar mass | 60.052 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 Acetic Acid (C₂H₄O₂).
Practice this calculation
Without looking above, write the atom count for C₂H₄O₂, then compute the molar mass. Check your answer against 60.052 g/mol.
Next challenge: how many grams are in 0.250 mol of Acetic Acid? Multiply 0.250 × 60.052 to get 15.013 g.
Physical and chemical properties
Physical properties
| Appearance | Colorless liquid (glacial); clear vinegar when dilute |
| Color | Colorless |
| Odor | Pungent, vinegar-like |
| State (STP) | Liquid |
| Density | 1.049 g/cm³ (glacial, 25 °C); ~1.01 g/cm³ (5% vinegar) |
| Melting point | 16.6 °C (glacial — 'glacial' threshold) |
| Boiling point | 118.1 °C |
| Solubility | Miscible with water, ethanol, ether; soluble in most organic solvents |
| Crystal structure | Monoclinic (solid below 16.6 °C) |
Chemical properties
| Classification | Carboxylic acid / weak organic acid |
| Family | Carboxylic acids (two-carbon) |
| Acidity | Weak acid (pKa = 4.76) |
| Polarity | Polar (carboxyl group, hydrogen bonding) |
| Geometry | Trigonal planar at carboxyl carbon |
| Oxidation states | C: −3 (methyl), +3 (carboxyl carbon) |
Applications
Industrial uses
- Vinyl acetate monomer production (PVA, emulsions, adhesives)
- Purified terephthalic acid (PTA) for PET polyester
- Cellulose acetate fibers and films
- Acetic anhydride precursor (aspirin, heroin synthesis historically)
Laboratory uses
- Weak acid standard for buffer preparation (acetic acid/sodium acetate)
- Solvent for recrystallization and organic synthesis
- Esterification reactions (Fischer esterification)
Vinegar preservation inhibits bacterial growth via pH reduction; acetic acid is a normal fatty acid metabolism intermediate (acetyl-CoA).
Preparation and production
Industrial: methanol carbonylation. Laboratory: oxidize ethanol with potassium dichromate or distil vinegar. Glacial acetic acid from acetic anhydride hydrolysis or fractional crystallization of dilute acid.
Methanol carbonylation dominates (>90% of new capacity). Fermentation accounts for food-grade vinegar.
Important reactions of Acetic Acid
CH₃COOH + NaOH → CH₃COONa + H₂O
- Reaction type
- Acid–base neutralization
- Conditions
- Aqueous, equimolar
- Explanation
- Weak acid–strong base neutralization forming sodium acetate; titration curve lacks sharp initial rise of strong acid.
- Products
- Sodium acetate and water
- Why it matters
- Buffer preparation, titration experiments
Related ideas: Weak acids · Neutralization · Salt hydrolysis
CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O
- Reaction type
- Fischer esterification
- Conditions
- Acid catalyst (H₂SO₄), heat, reflux
- Explanation
- Carboxylic acid condenses with alcohol to form ester and water; equilibrium driven by excess reagent or water removal.
- Products
- Ethyl acetate and water
- Why it matters
- Ester synthesis, solvent production
Related ideas: Esterification · Equilibrium · Organic synthesis
2 CH₃COOH → (CH₃CO)₂O + H₂O
- Reaction type
- Dehydration (anhydride formation)
- Conditions
- P₂O₅ or heat with acetyl chloride
- Explanation
- Two acetic acid molecules lose water to form acetic anhydride, a reactive acetylating agent.
- Products
- Acetic anhydride and water
- Why it matters
- Acetic anhydride production for aspirin synthesis
Related ideas: Anhydrides · Condensation reactions
CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂
- Reaction type
- Acid–carbonate
- Conditions
- Aqueous, room temperature
- Explanation
- Weak acid reacts with bicarbonate to release CO₂ — fizzing test distinguishes carboxylic acids from phenols.
- Products
- Sodium acetate, water, carbon dioxide
- Why it matters
- Baking soda–vinegar reactions, qualitative carboxylic acid test
Related ideas: Gas evolution · Weak acid strength · Qualitative analysis
History and discovery
Traces of acetic acid found in Egyptian urns (~3000 BCE). Pasteur proved acetic acid fermentation is biological (1864). Industrial synthesis replaced wood distillation (pyroligneous acid) in the early 20th century; Monsanto process (1966) revolutionized production economics.
Known since antiquity in vinegar; Louis Pasteur elucidated bacterial fermentation pathway in 1864.
Interesting facts
- Acetic acid molar mass 60.05 g/mol — close to 60 for quick mental math.
- The name 'glacial' refers to the ice-like appearance when pure acetic acid freezes at 16.6 °C.
- Acetic acid dimer (two molecules H-bonded) has doubled effective molar mass in vapor phase measurements.
- Vinegar has been used medicinally and as preservative for over 10,000 years.
Comparison with similar compounds
Acetic acid (60.05 g/mol, pKa 4.76) is weaker than formic acid (46.03 g/mol, pKa 3.77) due to methyl group's electron-donating inductive effect stabilizing the acid form.
Storage, handling, and safety
Glacial acetic acid in corrosion-resistant containers with tight seals (hygroscopic). Dilute vinegar stable indefinitely. Keep away from bases and oxidizers.
Glacial acetic acid causes severe burns and eye damage. Use fume hood and acid-resistant gloves. Vinegar (5%) is mild but avoid eye contact.
Glacial acetic acid is corrosive and flammable at elevated temperatures; vapors irritate respiratory tract.
- Corrosive burns (glacial form)
- Flammable at high concentrations and temperatures (flash point 39 °C glacial)
- Respiratory and eye irritation from vapors
Classification: GHS: Flam. Liq. 3, Skin Corr. 1A (glacial)
Exam notes and student tips
Exam notes
- Molar mass CH₃COOH = 2(12.01) + 4(1.008) + 2(16.00) = 60.05 g/mol.
- Weak acid: pKa = 4.76; Ka = 1.8 × 10⁻⁵.
- 1 mol acetic acid neutralized by 1 mol NaOH (monoprotic carboxylic acid).
- Functional group: carboxyl –COOH; gives –COO⁻ conjugate base.
Student tips
- Write CH₃COOH to identify carboxylic acid in isomer problems.
- Buffer: pH = pKa + log([A⁻]/[HA]) with acetate/acetic acid system.
- Link to acetyl-CoA in biochemistry (2-carbon unit, 60 g/mol fragment).
Common mistakes
- Treating acetic acid as strong acid — it is weak (partial dissociation).
- Confusing with ethanoic acid naming (same compound, IUPAC vs. common).
- Using C₂H₄O₂ without clarifying isomer (could theoretically be methyl formate).
Misconceptions
- Vinegar is not 'mostly acid' — 5% acetic acid means 95% water.
- Glacial acetic acid is not a solid at room temperature — it is liquid above 16.6 °C.
- All acids are not strong — acetic acid is weak despite corrosive concentrated form.
Practice questions
1. Calculate the molar mass of acetic acid (CH₃COOH).
Show answer
2(12.01) + 4(1.008) + 2(16.00) = 60.05 g/mol
2. What is the pH of 0.10 M acetic acid? (Ka = 1.8 × 10⁻⁵)
Hint: Use weak acid approximation: x = √(Ka × C).
Show answer
Ka = x²/0.10; x = [H⁺] ≈ 1.34 × 10⁻³ M; pH ≈ 2.87
3. How many grams of NaOH to neutralize 120 g acetic acid?
Show answer
120 g ÷ 60.05 g/mol = 2.0 mol; need 2.0 mol NaOH = 80 g
4. Why is acetic acid called a weak acid?
Show answer
Only ~1% dissociates in 0.1 M solution; equilibrium favors undissociated CH₃COOH.
Frequently asked questions about Acetic Acid
60.05 g/mol.
Chemistry of Acetic Acid
The sections above give the number you need for calculations. Here we look more closely at how Acetic Acid (C₂H₄O₂) behaves chemically—so the molar mass connects to real reactions, properties, and laboratory practice.
Acetic acid (CH₃COOH) is the simplest carboxylic acid with molar mass 60.05 g/mol, consisting of a methyl group bonded to a carboxyl group (–COOH). The carboxyl proton is weakly acidic (pKa = 4.76), partially dissociating in water: CH₃COOH ⇌ CH₃COO⁻ + H⁺. Household vinegar is ~5% acetic acid by mass; glacial acetic acid refers to the anhydrous form that freezes at 16.6 °C into ice-like crystals.
Acetic acid is produced industrially via methanol carbonylation: CH₃OH + CO → CH₃COOH (rhodium or iridium catalyst, Monsanto/Cativa process). Global demand exceeds 15 million tonnes annually, primarily for vinyl acetate monomer (PVA, adhesives), purified terephthalic acid (PET bottles), and cellulose acetate. Dilute acetic acid from fermentation (2C₂H₅OH + O₂ → 2 CH₃COOH + 2 H₂O, Acetobacter) gives vinegar its sour taste and preservative action.
C₂H₄O₂ can be written CH₃COOH to highlight the carboxyl functional group. The formula shows two carbons, four hydrogens, and two oxygens — one in the carbonyl (C=O) and one in the hydroxyl (O–H). The carboxyl carbon is sp² hybridized; the acidic proton is on the hydroxyl oxygen, not the methyl hydrogens.
Acetic acid is a weak Brønsted acid. It reacts with bases to form acetate salts, with alcohols to form esters (Fischer esterification), and with metals (Mg, Zn) to release H₂. It does not oxidize as readily as nitric acid. Concentrated acetic acid is corrosive and has a pungent vapor; it forms dimer hydrogen-bonded pairs in the gas phase and non-polar solvents.
Vinegar fermentation vs. glacial acetic acid
Household vinegar is a dilute (roughly 4–8%) aqueous solution of acetic acid produced by Acetobacter bacteria oxidizing ethanol in a two-step fermentation (sugar to ethanol, then ethanol to acetic acid), while 'glacial' acetic acid refers to the concentrated, nearly anhydrous form (≥99.5%) that freezes into ice-like crystals at 16.6 °C — the same chemical compound at drastically different concentrations, with correspondingly different handling hazards and uses.
Acetic acid vs. formic acid: carboxylic acid strength trend
Acetic acid (pKa 4.76) is a noticeably weaker acid than its simpler homolog formic acid (pKa 3.77), because acetic acid's methyl group donates electron density toward the carboxylate through the inductive effect, destabilizing the negative charge on the conjugate base relative to formate's unsubstituted structure — a clear, memorable illustration of how alkyl substitution affects carboxylic acid strength.
The carboxyl group: structure and reactivity hub
Acetic acid's reactivity centers entirely on its carboxyl group (–COOH), which combines a resonance-stabilized, partially acidic hydroxyl proton with an electrophilic carbonyl carbon; this dual character allows the same functional group to act as a Brønsted acid toward bases, a nucleophile-accepting electrophile toward alcohols in esterification, and a hydrogen-bond donor/acceptor responsible for its characteristic gas-phase dimerization.
Historical and industrial fermentation-to-synthesis shift
For most of human history, acetic acid was obtained exclusively through fermentation or wood distillation (pyroligneous acid); the 20th-century shift to methanol carbonylation (the Monsanto and later Cativa processes) transformed acetic acid from a fermentation-derived commodity into a large-scale petrochemical product, even as fermentation remains essential for food-grade vinegar production specifically.
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 176: Acetic acid data
- NIST Chemistry WebBook: Thermodynamic properties
- IUPAC: Carboxylic acid nomenclature