Difference Between Acetic Acid and Glacial Acetic Acid

Main Difference – Acetic Acid vs Glacial Acetic Acid

Acetic acid is the common name for ethanoic acid. It is a carboxylic acid which is composed of a carboxylic group attached to a –CH₃ group. Hence, its chemical formula is C₂H₄O₂. Acetic acid is commonly found in vinegar, which is a household essential often used for cooking. Glacial acetic acid is concentrated acetic acid. The main difference between acetic acid and glacial acetic acid is in their concentration; an acetic acid solution has a high amount of water whereas glacial acetic acid has less than 1% of water.

Key Areas Covered

1. What is Acetic Acid
      – Properties, Structure, Uses
2. What is Glacial Acetic Acid
      – Properties, Structure, Uses
3. What is the difference between Acetic Acid and Glacial Acetic Acid
      – Comparison of Key Differences

Key Terms: Acetic Acid, Ethanoic Acid, Acid, Vinegar, Glacial Acetic Acid, Diluted Acetic Acid, Concentrated Acetic Acid

What is Acetic Acid?

Acetic acid is a colorless solution which has a pungent odor. It is a major constituent in vinegar. Vinegar has about 3-9% of acetic acid. Acetic acid has many uses in both household and industry. It is used for cooking, cleaning, laundry and many other household needs. In industry, acetic acid is used for the production of vinyl acetate, acetic anhydride, esters, etc. Acetic acid has a density of 1.04g/cm³. Its melting point is about 16.5^oC.

Earlier, acetic acid was made industrially by air oxidation of acetaldehyde, by oxidation of ethanol and by oxidation of butane. But nowadays, acetic acid is industrially made by rhodium-iodine catalyzed carbonylation of methanol.

Figure 1: Chemical Structure of Acetic Acid

What is Glacial Acetic Acid?

Glacial acetic acid is the pure form of the acetic acid. It is composed of less than 1% water. The amount of acetic acid present in a glacial acetic acid solution is about 99.5%. Glacial acetic acid is a colorless liquid and is very corrosive. It is completely mixable with water. Glacial acetic acid is also called anhydrous (water-free) acetic acid due to the very little amount of water present there.

This acid is called glacial acetic acid because it can solidify into acetic acid crystals around a temperature of 16.7^oC. These crystals are dense than water; thus, they sink to the bottom of the container. Although acetic acid is safe to be added in food as vinegar, glacial acetic acid is not drinkable due to its corrosiveness.

The preparation of glacial acetic acid can be done by dipping acetic acid solution over a “stalactite” of solid glacial acetic acid. Then pure acetic acid will stick to the glacial acetic acid and impurities will run off with the liquid portion.

Glacial acetic acid is very useful in producing ester. Water is used along with glacial acetic acid to produce esters, If there’s already water in an acetic acid solution, it would affect the equilibrium of the production reaction and less amount of ester is obtained at the end than expected. In this case, glacial acetic acid is much better than a normal acetic acid solution.

Figure 2: Crystal Formation of Glacial Acetic Acid at 16.5oC.

Difference Between Acetic Acid and Glacial Acetic Acid

Definition

Acetic Acid: Acetic acid is a solution of acetic acid and water.

Glacial Acetic Acid: Glacial acetic acid is the concentrated acetic acid solution.

Water Content

Acetic Acid: Acetic acid contains more water and is in its diluted form.

Glacial Acetic Acid: Glacial acetic acid has less than 1% of water content and is concentrated with pure acetic acid.

Usage

Acetic Acid: Acetic acid causes no harm and is used as a food additive.

Glacial Acetic Acid: Glacial acetic acid is very corrosive and can cause injuries on the skin when touched.

Freezing

Acetic Acid: Acetic acid does not freeze and form crystals.

Glacial Acetic Acid: Glacial acetic acid form crystals at cooler temperatures around 16.5^oC.

Production

Acetic Acid: Acetic acid can be produced by rhodium-iodine catalyzed carbonylation of methanol.

Glacial Acetic Acid: Glacial acetic acid can be produced by dipping acetic acid solution over a “stalactite” of solid glacial acetic acid. Then pure acetic acid will stick to the glacial acetic acid and impurities will run off with the liquid portion.

Conclusion

Inside a laboratory, care should be taken when handling any kind of acid. Although acetic acid is a weak acid, it can cause injuries when it is in concentrated form. This concentrated acetic acid is called glacial acetic acid due to its ability to form crystals in cooler temperatures (16.5^oC). The main difference between acetic acid and glacial acetic acid is that acetic acid has a high amount of water present in the acetic acid solution whereas glacial acetic acid has less than 1% of water.

References:

1. Brown, William H. “Acetic acid (CH3COOH).” Encyclopædia Britannica. Encyclopædia Britannica, inc., n.d. Web. Available here. 07 June 2017. 
2. Helmenstine Anne Marie. “Glacial Acetic Acid Versus Ordinary Acetic Acid.” ThoughtCo. N.p., n.d. Web. Available here. 07 June 2017. 

Image Courtesy:

1. “Acetic-acid” (Public Domain) via Commons Wikimedia
2. “AceticAcid012” (Public Domain) via Commons Wikimedia