Final answer:
Pure ethanoic acid, also known as acetic acid, solidifies at 16.6°C and was historically called glacial acetic acid. Vinegar is a diluted form containing about 5% acetic acid and freezes at a lower temperature.
Step-by-step explanation:
The physical properties of pure ethanoic acid, commonly known as acetic acid, are such that it solidifies at a temperature of 16.6°C. This temperature is slightly lower than normal room temperature. Due to this characteristic, acetic acid was historically referred to as glacial acetic acid because it would "freeze" in the less heated laboratories of the late 19th and early 20th centuries, particularly in colder regions of North America and Europe.
In its pure form, acetic acid is colorless and has a strong odor. However, common household vinegar is a dilute solution, typically containing about 5% acetic acid, and it freezes at a lower temperature compared to pure acetic acid because of the presence of water, which disrupts the crystalline structure of the acetic acid molecules, lowering the freezing point of the solution.