Chapter 14, Problem 156AE

Quinine (C₂₀H₂₄N₂O₂) is the most important alkaloid derived from cinchona bark. It is used as an antimalarial drug. For quinine, $\text{p}{K}_{{\text{b}}_1}$ = 5.1 and $\text{p}{K}_{{\text{b}}_2}$ = 9.7 (pK_b = −log K_b). Only 1 g quinine will dissolve in 1900.0 mL of solution. Calculate the pH of a saturated aqueous solution of quinine. Consider only the reaction ${\text{Q+H}}_2\text{O}\rightleftharpoons {\text{QH}}^{+}+{\text{OH}}^{-}$ described by $\text{p}{K}_{{\text{b}}_1}$, where Q = quinine.