Boric acid () is a weak monoprotic acid in water due to Lewis acidity. It ionizes as . If , what is — Ionic Equilibrium Chemistry Question
Question
Boric acid ($H_3BO_3$) is a weak monoprotic acid in water due to Lewis acidity. It ionizes as $B(OH)_3 + H_2O \rightleftharpoons B(OH)_4^- + H^+$. If $K_a = 5.9 \times 10^{-10}$, what is the approximate pH of $0.3 \text{ M }$ boric acid?
Answer: A
💡 Solution & Explanation
$[H^+] = \sqrt{K_a C} = \sqrt{5.9 \times 10^{-10} \times 0.3} = \sqrt{1.77 \times 10^{-10}} \approx 1.33 \times 10^{-5} \text{ M}$. $pH = 5 - \log(1.33) \approx 4.87$.
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