Chapter 14, Problem 75E

Salicylic acid, ${\text{HOC}}_{\text{6}}{\text{H}}_{\text{4}}{\text{CO}}_{\text{2}}\text{H}$ , and its derivatives have been used as pain relievers for a long time. Salicylic acid occurs in small amounts in the leaves, bark, and roots of some vegetation (most notably historically in the bark of the willow tree). Extracts of these plants have been used as medications for centuries. The acid was first isolated in the laboratory in 1838.

(a) Both functional groups of salicylic acid ionize in water, with $K_a=1.0\times {10}^{-3}$ for the $-{\text{CO}}_{\text{2}}\text{H }$ group and $4.2\times {\text{ 10}}^{\text{-}}{}^{\text{13}}$ for the ^-OH group. What is the pH of a saturated solution of the acid (solubility = 1.8 g/L).

(b) Aspirin was discovered as a result of efforts to produce a derivative of salicylic acid that would not be irritating to the stomach lining. Aspirin is acetylsalicylic acid, ${\text{CH}}_{\text{3}}{\text{CO}}_{\text{2}}{\text{C}}_{\text{6}}{\text{H}}_{\text{4}}{\text{CO}}_{\text{2}}\text{H}\text{.}$

The $-C{O}_{2}H$ functional group is still present, but its acidity is reduced, ${\text{K}}_{\text{a}}\text{=3}{\text{.0 10}}^{\text{-4}}$ . What is the pH of a solution of aspirin with the same concentration as a saturated solution of salicylic acid (See Part a).