A solution has initially and . of , of . The only incorrect statement for the solution is () — Ionic Equilibrium Chemistry Question
Question
A solution has initially $0.1\text{ M} – \text{HCOOH}$ and $0.2\text{ M} – \text{HCN}$. $K_a$ of $\text{HCOOH} = 2.56 \times 10^{-4}$, $K_a$ of $\text{HCN} = 9.6 \times 10^{-10}$. The only incorrect statement for the solution is ($\log 2 = 0.3$)
💡 Solution & Explanation
Because HCOOH is a much stronger acid than HCN, it dictates the $[\text{H}^+]$. $[\text{H}^+] \approx \sqrt{K_{a1}C_1} = \sqrt{2.56 \times 10^{-4} \times 0.1} \approx 5 \times 10^{-3}\text{ M}$. Note: The options a, b, c reflect values assuming $C_{\text{HCOOH}} = 0.01\text{ M}$ originally intended by the author, but regardless of that typographical error, a $\text{pOH}$ of 2.8 strictly implies a basic/alkaline solution ($\text{pH} = 11.2$), which is physically impossible for a mixture of two weak acids. Thus (d) is definitively incorrect in all scenarios.