The pH of formic acid depends on its concentration. A 0.1 M solution of formic acid has a pH of about 2.4, while a 1 M solution has a pH of about 1.7. This is because formic acid is a weak acid, which means that it does not completely dissociate in water. The higher the concentration of formic acid, the more hydrogen ions (H+) are released, which lowers the pH.