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What it is. Glacial acetic acid (ethanoic acid, CH3COOH) is acetic acid in its nearly water-free form, assayed at 99.7% minimum for ACS grade. It is a clear, colorless liquid with a sharp vinegar odor and one of the most widely used organic acids in analytical, synthetic, pharmaceutical, and teaching labs.
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Why it is called glacial. Pure acetic acid freezes at about 16.6 °C (62 °F), only a few degrees below room temperature. In a cool stockroom or during winter shipping, it forms clear, ice-like crystals, which gave the concentrated grade its name. Freezing does not degrade the acid; it returns to a uniform liquid when gently warmed to room temperature. Acetic acid also contracts slightly as it freezes.
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Two grades for different requirements. The 500 mL size (ZA0075-16) is certified to ACS reagent specifications for analytical and bench work. The 2.5 L size (ZA0075-2.5L) carries a dual ACS/USP designation with a 99.5 to 100.5% USP assay range, so a single lot can serve both analytical testing and procedures that reference the United States Pharmacopeia monograph.
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Purity you can document. ACS reagent glacial acetic acid is held to tight limits that matter in trace and titration work: 99.7% minimum assay, color no darker than 10 APHA, acetic anhydride at 0.01% or less, chloride at 1 ppm or less, heavy metals (as Pb) at 0.5 ppm or less, and residue after evaporation at 0.001% or less. It must also pass a dilution test, which screens for impurities that cause haze when the acid is diluted with water.
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Acid strength and behavior in water. Acetic acid is a weak acid with a pKa of about 4.76, so only a small fraction ionizes in dilute solution. It mixes completely with water, ethanol, and ether. Diluting glacial acid with water releases heat and causes slight volume contraction, so make dilutions by adding acid to water in stages and allowing it to cool before bringing to volume.
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A useful solvent in its own right. Glacial acetic acid is a polar protic solvent with a low dielectric constant, allowing it to dissolve many organic compounds and some inorganic salts. Because it is a weaker proton acceptor than water, it enhances the apparent basicity of weak bases, which is why perchloric acid in glacial acetic acid is the standard titrant system for non-aqueous assays of amines and other weak bases in pharmacopeial methods.
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Building acetate buffers. Combined with sodium acetate, glacial acetic acid forms acetate buffers that hold pH between about 3.6 and 5.6. Equal molar amounts of acid and acetate give a pH close to the pKa of 4.76, and changing the ratio moves the pH up or down. Pair it with Lab Pro's Sodium Acetate Anhydrous Powder for buffer preparation in enzyme assays, chromatography, and sample preparation.
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Flammability and exposure at a glance. The glacial acid has a flash point near 40 °C (104 °F) and a lower explosive limit of about 4% in air, so its vapors can ignite above warm liquid. Its vapor is about twice as dense as air and irritates the eyes and respiratory tract; OSHA sets a permissible exposure limit of 10 ppm as an 8-hour average.
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Where it is used. In the lab, glacial acetic acid is used for acetate buffers, non-aqueous titrations, acetylation reactions, recrystallization of organic compounds, pH adjustment, and histology fixatives such as Carnoy's solution. Industrially, acetic acid is a major feedstock for vinyl acetate monomer, cellulose acetate, and acetic anhydride, making it one of the most-produced organic chemicals.
Technical Specifications
| Chemical Name |
Acetic acid, glacial |
| CAS Number |
64-19-7 |
| EC Number |
200-580-7 |
| PubChem CID |
176 |
| Synonyms |
Ethanoic acid, methanecarboxylic acid |
| Formula |
C2H4O2 (CH3COOH) |
| Molecular Weight |
60.05 g/mol |
| Grade |
ACS (500 mL); ACS/USP (2.5 L) |
| Assay |
ACS: 99.7% min; USP: 99.5 to 100.5% |
| Appearance |
Clear, colorless liquid with pungent vinegar odor |
| Freezing / Melting Point |
16.6 °C (62 °F) |
| Boiling Point |
118 °C (244 °F) |
| Density |
1.049 g/mL at 20 °C |
| Flash Point |
40 °C (104 °F) |
| Autoignition Temperature |
427 °C (801 °F) |
| Lower Explosive Limit |
4% by volume |
| Vapor Pressure |
1.52 kPa at 20 °C |
| Vapor Density |
2.1 (air = 1) |
| pKa |
4.76 (25 °C) |
| Solubility |
Miscible with water, ethanol, and ether |
| Color (APHA) |
10 max (ACS) |
| Acetic Anhydride |
0.01% max (ACS) |
| Chloride (Cl) |
1 ppm max (ACS) |
| Heavy Metals (as Pb) |
0.5 ppm max (ACS) |
| Residue after Evaporation |
0.001% max (ACS) |
| Refractive Index |
1.372 (20 °C) |
| Package Sizes |
500 mL; 2.5 L |
Available Variants
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ZA0075-16: 500 mL, ACS reagent grade, for routine analytical and bench use.
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ZA0075-2.5L (AA9010-625): 2.5 L, dual ACS/USP grade, for higher-volume labs and USP-referenced work.
Applications / Common Uses
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Acetate buffer preparation: Combined with sodium acetate to make buffers in the pH 3.6 to 5.6 range for enzyme assays, chromatography, and sample prep.
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Non-aqueous titration: Serves as the solvent for perchloric acid titrations of weak bases, a common pharmacopeial assay method.
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Organic synthesis and recrystallization: Acts as a reaction solvent for acetylations and a recrystallization solvent for organic compounds.
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pH adjustment: Lowers pH in formulations where a weak, volatile acid is preferred over a mineral acid.
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Histology and microscopy: Used in fixative mixtures and as an acidifying or clearing agent in staining procedures.
Storage, Handling & Shipping
Caution: Glacial acetic acid is corrosive and flammable. It causes severe skin burns and eye damage, and its vapor irritates the eyes, nose, and respiratory tract. Handle it in a fume hood, away from ignition sources, wearing chemical splash goggles, a face shield, a lab coat, and butyl rubber or other acid-rated gloves.
Store glacial acetic acid tightly closed in a cool, dry, well-ventilated flammables or corrosives area, separate from oxidizers and bases, and away from heat, sparks, and open flames. Because it freezes near 16.6 °C, it may solidify in cold rooms; thaw it slowly at room temperature, never with direct heat, and mix before use. When diluting, always add acid to water.
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Incompatible materials: Strong oxidizers (including nitric, chromic, and perchloric acid), strong bases, peroxides, and many metals.
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Exposure limits: OSHA PEL 10 ppm TWA; NIOSH REL 10 ppm TWA, 15 ppm STEL.
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Spill response: Remove ignition sources, ventilate, and absorb with an acid-neutralizing spill product. Do not flush concentrated acid to drains.
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First aid: Skin or eyes: flush with water for at least 15 minutes and seek medical attention. Inhalation: move to fresh air.
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GHS signal word: Danger. Flammable liquid and vapor; causes severe skin burns and eye damage.
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NFPA 704: Health 3, Flammability 2, Instability 0.
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DOT / shipping: UN2789, Acetic acid, glacial, Class 8 (subsidiary Class 3), Packing Group II.
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