Here's some interesting information about PH:
Properties of Vinegar - pH of Vinegar
The term "pH" is derived from "potential hydrogen" and refers to the amount of hydrogen ions present in solution.
Mathematically, pH is equal to the negative logarithm (base 10) of the hydrogen ion concentration in moles per liter, so if the pH of a solution decreases by 1 pH unit then its hydrogen ion concentration increases by ten times.
Pure water has a pH of 7 and is neutral whereas anything with a pH less than 7 is acidic and anything with a pH greater than 7 is basic.
The pH of vinegar depends upon how much acid is present, but most commercial distilled white vinegars contain 5% acetic acid and have a pH of about 2.4.
To put that in perspective, the following table compares the pH of vinegar to some other common solutions:
(Sorry about the small size. If you click once on the image it will enlarge.)
Pete