Vinegar has a pH of 2.2, according to Dr. Anne Marie Helmenstine, a contributor to About.com. Anything with a pH less than 7 is considered an acid.
Vinegar contains water and 5 to 10 percent acetic acid. Its acidity makes it useful for cleaning, getting rid of the sticky residue from price tags and removing stains from carpeted areas. Vinegar is also used to unclog drains and eliminate odors caused by tobacco smoke, pets and foods. When someone combines vinegar with baking soda, a base, the two substances react to form carbonic acid and sodium acetate. The carbonic acid decomposes into carbon dioxide gas, which escapes in the form of bubbles.