What Is Glacial Acetic Acid?

Understand the Difference Between Glacial Acetic Acid and Regular Acetic Acid

This is the structure of acetic acid. Glacial acetic acid is water containing 1% or less water.
This is the structure of acetic acid. Glacial acetic acid is water containing 1% or less water. LAGUNA DESIGN / Getty Images

Acetic acid (CH3COOH) is the common name for ethanoic acid. It is an organic chemical compound that has distinctive pungent odor and sour flavor, recognizable as the scent and flavor of vinegar. Vinegar is about 3-9% acetic acid.

How Glacial Acetic Acid Is Different

Acetic acid that contains a very low amount of water (less than 1%) is called anhydrous (water-free) acetic acid or glacial acetic acid.

The reason it's called glacial is because it solidifies into solid acetic acid crystals just cooler than room temperature at 16.7 °C, which ice. Removing the water from acetic acid lowers its melting point by 0.2 °C.

Glacial acetic acid may be prepared by dripping acetic acid solution over a "stalactite" of solid acetic acid (which could be considered to be frozen). Like a water glacier contains purified water, even if it's floating in the salty sea, pure acetic acid sticks to the glacial acetic acid, while impurities run off with the liquid.

Caution: Although acetic acid is considered a weak acid, safe enough to drink in vinegar, glacial acetic acid is corrosive and can injure skin on contact.

More Acetic Acid Facts

Acetic acid is one of the carboxylic acids. It is the second simplest carboxylic acid, after formic acid. The main uses of acetic acid are in vinegar and to make cellulose acetate and polyvinyl acetate.

Acetic acid is used as a food additive (E260), where it is added for flavor and to regular acidity. It's an important reagent in chemistry, too. Worldwide, around 6.5 metric tons of acetic acid are used per year, of which approximately 1.5 metric tons per year are produced by recycling. Most acetic acid is prepared using petrochemical feedstock.

Acetic Acid and Ethanoic Acid Naming

The IUPAC name for the chemical is ethanoic acid, a name formed using the convention of dropping the final "e" in the alkane name of the longest carbon chain in the acid (ethane) and adding the "-oic acid" ending.

Even though the formal name is ethanoic acid, most people refer to the chemical as acetic acid. In fact, the usual abbreviation for the reagent is AcOH, partly to avoid confusion with EtOH, a common abbreviation for ethanol. The common name "acetic acid" comes from the Latin word acetum, which means vinegar.

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Helmenstine, Anne Marie, Ph.D. "What Is Glacial Acetic Acid?" ThoughtCo, May. 28, 2016, thoughtco.com/what-is-glacial-acetic-acid-4049300. Helmenstine, Anne Marie, Ph.D. (2016, May 28). What Is Glacial Acetic Acid? Retrieved from https://www.thoughtco.com/what-is-glacial-acetic-acid-4049300 Helmenstine, Anne Marie, Ph.D. "What Is Glacial Acetic Acid?" ThoughtCo. https://www.thoughtco.com/what-is-glacial-acetic-acid-4049300 (accessed February 18, 2018).