Vinegar is a dilute acid that can be made more dilute using water, or it can be neutralized using a base, but it cannot be made into a base itself. The term "pH" stands for "potential hydrogen" -- the more free-floating hydrogen ions in a solution, the more acidic the solution is. Vinegar's pH will always remain at a number lower than neutral, no matter how dilute it is, because vinegar is an acid.
Vinegar Is a Dilute Acid
Vinegar is a diluted form of acetic acid. Acetic acid makes up from 4 percent to 6 percent of the vinegar's content, depending on the brand and type of vinegar. Water makes up nearly all the rest of the vinegar's content, though traces of fiber, vitamins and other compounds present in the foods used to supply the sugars necessary for the production of vinegar may also remain. The acetic acid, which can be represented as CH3COOH, forms in a naturally dilute solution when vinegar is made. Distilled white vinegar can be expected to contain roughly 5 percent acetic acid, and its pH can expected to be roughly 2.4.
Production of Vinegar
When a sugar, which can be represented as C6H12O6, is combined with yeast, it forms alcohol and CO2 -- this process is called fermentation. The carbon dioxide is released as a vapor while the alcohol remains in liquid form. The alcohol, which can be represented as C2H5OH, then interacts with oxygen and microorganisms in the air. The type of oxygen molecule that interacts with the alcohol molecule is O2, and the type of microorganism is an acetobacter, a type of tiny bacteria. Once the bacteria and oxygen have metabolized and reacted, respectively, to the alcohol, a solution of acetic acid and water remains. The vinegar's chemical makeup can be represented as CH3COOH (the acetic acid molecule) + H2O (the water molecule).
Distilled water has a neutral pH of 7, which means that water is neither an acid nor a base. However, because the water that has not been distilled comes into contact with chemicals in the atmosphere, pipes, soil and rocks, it picks up chemicals that may change its pH. For example, the National Atmospheric Deposition Program of the United States has mapped out the pH of water that has fallen as precipitation throughout the country. That water has a pH of roughly 5.0 to 6.0 on the West Coast, and the pH of precipitation water falls to roughly 4.0 to 5.0 on the East Coast. The lower the pH of the water used to dilute vinegar, the more limited the water's ability is to raise the pH of the vinegar. Further dilution of vinegar would raise its pH from around 2.4 -- however, since water is not a base, even very dilute vinegar would remain an acid, even as its pH grows higher and it comes closer to neutral.
Order to neutralize vinegar's pH to that of water it must be combined with a base in a reaction that will produce water using the oxygen and hydrogen atoms already present in the vinegar (and in the base it's to be combined with). A common base used to neutralize vinegar is baking soda, which can be represented as NaHCO3. When combined with baking soda, for example, the vinegar's hydrogen ions and the baking soda's bicarbonite ions combine to produce carbonic acid, which spontaneously decomposes into a vapor of carbon dioxide, and liquid water.