Glacial acetic acid is acetic acid that contains little to no water. In other words, it is a purified or concentrated form of anhydrous acetic acid. It is called “glacial” because it freezes and forms crystals resembling ice at a temperature slightly below room temperature (16.6 °C or 61.9 °F). In contrast, regular acetic acid contains water, so freezing point depression gives it a lower freezing point (no “glacier” effect).
Difference Between Acetic Acid and Glacial Acetic Acid
The principal difference between acetic acid and glacial acetic acid is how much water it contains. But, there are other differences.
| Acetic Acid | Glacial Acetic Acid |
|---|---|
| solution of acetic acid in water | concentrated acetic acid containing very little water |
| more water than acid | less than 1% water |
| safe in food or on skin | highly corrosive, irritates and injures eyes, skin, and mucous membranes |
| does not freeze under ordinary storage conditions | forms ice-like crystals under cool storage conditions |
| naturally-occurring | usually synthesized in a lab |
| commercially produced by carbonylation of methanol using a rhodium-iodine catalyst | obtained by solidifying acetic acid around a “stalactite” of glacial acetic acid |
While many organisms produce acetic acid, both the regular variety and glacial acetic acid are petroleum products commercially. It’s also widely recycled. For example, around 1.5 metric tons of the global use of 6.5 metric tons is recycled chemical.
Dilute acetic acid is a source of glacial acetic acid because pure acetic acid stick to “stalactites” of solid glacial acetic acid. This is comparable to the way fresh water forms over icebergs in a salty sea. For example, dripping vinegar over frozen glacial acetic acid further dilutes the vinegar while growing the amount of glacial acetic acid.
Is Vinegar Glacial Acetic Acid?
Vinegar contains acetic acid, but it is not glacial acetic acid. Vinegar is mostly water with between 4% and 8% acetic acid, by volume. So, glacial acetic acid is concentrated, purified acetic acid, while vinegar is dilute acetic acid that also contains flavorings and other chemicals.
Acetic Acid Facts
The systematic name for acetic acid is actually ethanoic acid. Its common name comes from the word acetum, which is Latin for “vinegar.” The chemical formula of acetic acid is CH3COOH. Other forms of the formula include CH3CO2H, C2H4O2, and HC2H3O. Rather than write out the formula, a symbol for acetic acid is AcOH (similar to EtOH for ethanol) or HAc.
Acetic acid is a weak acid. What this means is that it does not fully dissociate into ions in water. It is colorless when pure. Both plants and animals produce acetic acid. Fruits release acetic acid as they ripen. In humans and other primates, the compound acts as an antibacterial agent in vaginal fluid. Anaerobic bacteria, such as some members of Acetobacterium and Clostridium, convert sugars directly into acetic acid.
Acetic Acid Uses
Both regular dilute acetic acid and glacial acetic acid serve many uses.
- In medicine, acetic acid is a highly effective disinfectant. It acts against Pseudomonas, Enterococcus, Staphylococcus, and Streptococcus. It kills antibiotic resistant bacteria. Other uses include cervical cancer screening and lysing red blood cells to make white blood cell examination easier. Spraying acetic acid on livestock silage keeps down fungal and bacterial growth.
- Acetic acid as vinegar is a familiar cleaning agent. On its own, it’s an excellent glass cleaner.
- Vinegar adds a tangy flavor to recipes and reacts with baking soda to make bubbles that help baked goods rise. It’s a pickling agent and occurs in condiments, such as ketchup, mustard, and mayonnaise.
- Commercially, glacial acetic acids finds use in ink, perfume, and dye manufacture. It is a feedstock in other chemical production processes.
- In chemistry, acetic acid is a valuable solvent. It is particularly handy in recrystallization experiments.
References
- Armarego, W.L.F.; Chai, Christina (2009). Purification of Laboratory Chemicals (6th ed.). Butterworth-Heinemann. ISBN 978-1-85617-567-8.
- Barclay, J. (1866). “Injection of Acetic Acid in Cancer.” The BMJ. 2(305): 512–512. doi:10.1136/bmj.2.305.512-a
- Cheung, Hosea; Tanke, Robin S.; Torrence, G. Paul. (2011). “Acetic Acid”. Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a01_045.pub2
- Gupta, Chhavi, et al. (2015). “Role of Acetic Acid Irrigation in Medical Management of Chronic Suppurative Otitis Media: A Comparative Study.” Indian Journal of Otolaryngology and Head & Neck Surgery. Springer India. doi:10.1007/s12070-014-0815-2
- Roger, Elizabeth; Nwosu, Oguchi (2014). “Diagnosing Cervical Dysplasia Using Visual Inspection of the Cervix with Acetic Acid in a Woman in Rural Haiti.” International Journal of Environmental Research and Public Health. MDPI. doi:10.3390/ijerph111212304