This is a bit of a trick question! Acetic acid is the main component of vinegar. It's not that they don't mix well, it's that vinegar is simply a diluted solution of acetic acid in water.

Here's a breakdown:

* Acetic acid is a colorless liquid with a pungent smell. It's the active ingredient in vinegar.

* Vinegar is a solution of acetic acid in water, typically at a concentration of around 4-8%. It also contains other trace compounds like sugars, minerals, and bacteria.

So, vinegar and acetic acid do mix perfectly because vinegar is essentially acetic acid diluted with water. The difference is in concentration and the presence of additional components in vinegar.