Pure acetic acid is called “glacial” because it freezes into clear, ice-like crystals at about 16.6 °C (61.9 °F), so it looks like a tiny glacier inside the bottle. Glacial acetic acid is simply the nearly pure, water-free form of acetic acid (CH₃COOH, CAS 64-19-7), usually 99.5% or higher. In this guide you will find every key property in one place: formula, molar mass, density, melting and boiling points, pH, molar concentration, and the real safety hazards.
What Is Glacial Acetic Acid?
Glacial acetic acid is the anhydrous (water-free) form of acetic acid. It is the exact same molecule you find in vinegar — just without the water. The word “glacial” does not mean the liquid is kept frozen. It describes what happens when the pure liquid gets cold.
Why Is Pure Acetic Acid Often Called Glacial Acetic Acid?
Because pure acetic acid turns into translucent, ice-like crystals just below room temperature. Its freezing point is 16.6 °C (61.9 °F). In the 1700s and 1800s, chemists working in cold, unheated labs noticed their bottles of concentrated acid became a glassy solid that looked like glacial ice. The name stuck. It was even used as a quick purity test: only near-pure acid freezes so easily, because even a little water sharply lowers the freezing point.
Glacial Acetic Acid at a Glance
| Property | Value |
|---|---|
| IUPAC Name | Ethanoic acid |
| Common Formula | CH₃COOH (C₂H₄O₂) |
| CAS Number | 64-19-7 |
| Molar Mass | 60.05 g/mol |
| Purity (Glacial) | ≥ 99.8% |
| Density | 1.049 g/cm³ (20 °C) |
| Melting Point | 17 °C (62.6 °F) |
| Boiling Point | 118 °C (244 °F) |
| pKa | 4.76 |
| Flash Point | 43 °C (109.4 °F) |
| UN / Hazard Class | 2789 · Class 8 corrosive |
| Appearance | Clear colorless liquid, sharp vinegar odor |
| Solubility | Miscible with water |
Glacial Acetic Acid Formula and Molar Mass
Glacial acetic acid has the formula CH₃COOH, also written C₂H₄O₂. It is a carboxylic acid with two carbon atoms. Its molar mass is 60.05 g/mol. The –COOH group (the carboxyl group) shown in the structure below is what gives it acidic behavior.
Glacial Acetic Acid Density
Glacial acetic acid is slightly heavier than water. Its density is about 1.049 g/cm³ at 20 °C (often rounded to 1.05). That means it sinks in water. Household vinegar is close to 1.00–1.01 g/cm³, so the two do not mix evenly if poured together slowly.
Glacial Acetic Acid Melting Point
The melting (freezing) point is 17 °C (62.6 °F). This is the temperature where glacial acetic acid turns solid. It also tends to “supercool”: it can stay liquid below 16.6 °C until it is shaken or scratched, then it freezes almost instantly. Keep storage above 17 °C so it does not solidify in the drum.
Boiling Point of Glacial Acetic Acid
Glacial acetic acid boils at about 118 °C (244 °F) at normal pressure. That is much higher than water (100 °C) and far above vinegar (which is mostly water). The high boiling point makes it a useful high-temperature solvent in labs.
Glacial Acetic Acid pH and Molar Concentration
Pure glacial acetic acid is not an aqueous solution, so it has no standard pH number. Its pKa is 4.76, which makes it a weak acid. When dissolved, a 1.0 M solution has a pH of about 2.4. As a pure liquid, its molar concentration is very high — about 17.4 M (from 1.049 g/mL ÷ 60.05 g/mol). That is why even a small splash is dangerous: it is far stronger than vinegar (roughly 1 M).
Glacial Acetic Acid vs Acetic Acid
They are the same chemical. “Acetic acid” is the compound. “Glacial acetic acid” is the pure, water-free version. Vinegar is only 4–8% acetic acid. See the side-by-side comparison below.
| Property | Vinegar (~5%) | Glacial (≥99.5%) |
|---|---|---|
| Acetic Acid Content | 4–8% | ≥ 99.5% |
| Freezing Point | ~ −2 °C | 16.6 °C |
| Boiling Point | ~ 100 °C | 118 °C |
| Density | ~ 1.01 g/cm³ | 1.049 g/cm³ |
| Hazard | Safe to eat | Corrosive, flammable |
| Common Use | Food, cleaning | Industry, labs |
Safety Data Sheet: Glacial Acetic Acid Hazards
Glacial acetic acid is both corrosive and flammable. Key SDS facts:
- GHS labels: Corrosive (H314), Flammable liquid/vapor (H226), Causes respiratory irritation (H335).
- NFPA ratings: Health 3, Flammability 2, Instability 0.
- UN 2789, Class 8 (corrosive), Packing Group II.
- Skin or eye contact causes severe burns and possible permanent eye damage.
- Vapors irritate the nose, throat, and lungs.
- Flash point 39 °C (102 °F); keep away from heat, sparks, and flames.
- Store above 17 °C, away from strong bases and oxidizers (e.g., nitric acid, peroxides).
- Required PPE: nitrile gloves, splash goggles, lab coat, fume hood.
First Aid at a Glance
- Skin: flush with water 15+ minutes, remove clothing, get medical help.
- Eyes: rinse 20+ minutes, seek emergency care.
- Inhaled: move to fresh air.
- Swallowed: do NOT induce vomiting; rinse mouth; call poison control.
The Bottom Line
Pure acetic acid earns the name “glacial” because it freezes into ice-like crystals at 17 °C. Beyond the name, it is a powerful, corrosive, high-purity chemical — not the mild vinegar in your kitchen. Keep its formula (CH₃COOH), molar mass (60.05 g/mol), density (1.049 g/cm³), and boiling point (118 °C) in mind, and always treat the hazards with respect.