Aspirin, or acetylsalicylic acid, is a weak acid. Its pKa is around 3.5. This means that at a pH of 3.5, half of the aspirin molecules are in their acidic form (acetylsalicylic acid) and half are in their basic form (acetylsalicylate).

Therefore, the approximate pH of aspirin itself is around 3.5. However, it's important to note that the pH of an aspirin solution will depend on the concentration of aspirin and the presence of other substances.