Calculate the acid dissociation constant, , for a aqueous solution of if its is at . — Ionic Equilibrium Chemistry Question
Question
Calculate the acid dissociation constant, $K_a$, for a $10^{-2} \text{ M}$ aqueous solution of $HCN$ if its $pOH$ is $10$ at $25^\circ C$.
Answer: C
💡 Solution & Explanation
If $pOH = 10$, then $pH = 14 - 10 = 4$. Therefore, $[H^+] = 10^{-4} \text{ M}$. Using the weak acid approximation $[H^+] = \sqrt{K_a \times C}$, we have $10^{-4} = \sqrt{K_a \times 10^{-2}}$. Squaring both sides yields $10^{-8} = K_a \times 10^{-2}$, so $K_a = 10^{-6}$.
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