Salicylic acid, HOC6H4CO2H, and its derivative have been used as pain reliever for a long time. Salicylic acid occurs in small amount in the leaves, bark, and roots of some vegetation (most notably historically in the bark of the willow tree). Extracts of this plant have been used as medication for century. The acid was first isolated in the laboratory in 1838.
(a) Both functional groups of salicylic acid ionize in water, with K a = 1.0 × 10−3 for the—CO2H group and 4.2 × 10−13 for the −OH group. What is the pH of a saturated solution of the acid (solubility = 1.8 g/L).