Question

Why pure acetic acid is called glacial acetic acid?

Answer 1

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.