Q54 / 197 · NEET 2009 (Mains) · Chemistry
The dissociation constants for acetic acid and $\mathrm{HCN}$ at $25^{\circ} \mathrm{C}$ are $1.5 \times 10^{-5}$ and $4.5 \times 10^{-10}$, respectively. The equilibrium constant for the equilibrium -
$$
\mathrm{CN}^{-}+\mathrm{CH}_3 \mathrm{COOH} \rightleftharpoons \mathrm{HCN}+\mathrm{CH}_3 \mathrm{COO}^{-}
$$
would be :
- Correct answerA$3.0 \times 10^4$
- B$3.0 \times 10^5$
- C$3.0 \times 10^{-5}$
- D$3.0 \times 10^{-4}$
Solution
$$
\begin{aligned}
\mathrm{K}_{\mathrm{c}} & =\mathrm{K}_{\mathrm{a}\left(\mathrm{CH}_3 \mathrm{COOH}\right)} \times \frac{1}{\mathrm{~K}_{\mathrm{a}(\mathrm{HCN})}} \\
& =1.5 \times 10^{-5} \times \frac{1}{4.5 \times 10^{-10}} \\
& \cong 3 \times 10^4
\end{aligned}
$$
Hence, the correct answer is option: 'A'.