[Pulcinella]

Well not in terms of pH, but there are several acids that can exist as a pure liquid, undiluted by water. Pure vinegar, undiluted by water, is called glacial acetic acid. It is something that can be bought from a chemical company. Because there is no water, there isn't really a pH. That doesn't mean it isn't incredibly hazardous, though.

[aninhumer]

>Because there is no water, there isn't really a pH.

Could you elaborate? Wikipedia doesn't seem to suggest water is necessary (it talks about moles per unit volume) but I may be misunderstanding something.

[tim333]

The definition of pH is pretty much a measure of the proton concentration of things dissolved in water. You can look at similar measures in non aqueous solution but then it doesn't fit the definition properly.

[tomsmeding]

I'd say you have moles per unit volume of H3O+ ions. These form as the combination of H+ ions (readily present in copious amounts of acid) and crucially, H2O molecules.

[mirimir]

On the other hand, pure oleic acid isn't especially toxic. It's a major component of Lorenzos oil.