Chapter 14, Problem 84E

Salicylic acid, HOC₆H₄CO₂H, 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) Bath functional groups of salicylic acid ionize in water, with $K_a=1.0\times {10}^{-3}$ for the—CO₂H group and $4.20\times {10}^{-13}$ 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, CH₃CO₂C₆H₄CO₂H. The -CO₂H functional group is still present, but its acidity is reduced, $K_a=3.0\times {10}^{-4}$. What is the pH of a solution of aspirin with the same concentration as a saturated solution of salicylic acid (See Part a).

(c) Under some conditions, aspirin reacts with water and forms a solution of salicylic acid and acetic acid:

${\text{CH}}_3{\text{CO}}_2{\text{C}}_6{\text{H}}_4{\text{CO}}_2\text{H}\left(aq\right)+{\text{H}}_2\text{O}\left(l\right)\to {\text{HOC}}_6{\text{H}}_4{\text{CO}}_2\text{H}\left(aq\right)+{\text{CH}}_3{\text{CO}}_2\text{H}\left(aq\right)$

i. Which of the acids, salicylic acid or acetic acid, produces more hydronium ions in such a solution?

ii. What are the concentrations of molecules and ions in a solution produced by the hydrolysis of 0.50 g of aspirin dissolved in enough water to give 75 mL of solution?