Ionic EquilibriumhardNUMERICAL

At , two weak monoprotic acids and have dissociation constants and respectively. Calculate the ratioIonic Equilibrium Chemistry Question

Question

At $25^\circ C$, two weak monoprotic acids $HA_1$ and $HA_2$ have dissociation constants $K_{a1} = 9 \times 10^{-6}$ and $K_{a2} = 1 \times 10^{-10}$ respectively. Calculate the ratio of their degree of dissociations ($\alpha_1 / \alpha_2$) if both acids are present in separate solutions of the exact same molar concentration $C$ (Assume $\alpha \ll 1$ for both).

Answer: 300

💡 Solution & Explanation

From Ostwald's dilution law for weak acids, $\alpha = \sqrt{K_a / C}$. At the same concentration, the ratio of degrees of dissociation is $\alpha_1 / \alpha_2 = \sqrt{K_{a1} / K_{a2}}$. Substituting the values gives $\sqrt{(9 \times 10^{-6}) / (10^{-10})} = \sqrt{9 \times 10^4} = 300$.

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