Question

Quinine is a weak base that is used to flavour tonic water and treat malaria. The Kb for quinine is 3.3 x 10^-6. Calculate the pH of a 1.7 x 10^-2 mol/L solution of quinine.

Answer 1

Answer to Question #58554, Chemistry / Other

Quinine is a weak base that is used to flavour tonic water and treat malaria. The Kb for quinine is $3.3 \times 10^{-6}$. Calculate the pH of a $1.7 \times 10^{-2} \, \text{mol/L}$ solution of quinine.

Solution:

$[\mathrm{OH}^{-}] = x$

$$K_{b} = \frac{[HB^{+}] [OH^{-}]}{[B]} = \frac{x^{2}}{c - x}$$

Since $x \ll c$

$$K_{b} = \frac{x^{2}}{c}$$ $$x = \sqrt{K_{b}c} = \sqrt{3.3 \times 10^{-6} \times 1.7 \times 10^{-2}} = \sqrt{5.61 \times 10^{-8}} = 2.37 \times 10^{-4}$$ $$pOH = -\log[OH^{-}] = 3.63$$ $$pH = 14 - pOH = 14 - 3.63 = 10.37$$

Answer:

10.37

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