Question

The dissociation constants for acetic acid and HCN at ${25}^{\circ }C$ are $1.5\times {10}^{-5}$ and $4.5\times {10}^{-10}$, respectively. The equilibrium constant for the equilibrium, $C{N}^{-}+C{H}_{3}COOH\rightleftharpoons HCN+C{H}_{3}CO{O}^{-}$ would be?

• A. $3.0\times {10}^5$
• B. $3.0\times {10}^{-5}$
• C. $3.0\times {10}^{-4}$
• D. $3.0\times {10}^4$

Answer 1

The correct option is D $3.0\times {10}^4$

$C{H}_{3}COOH\iff C{H}_{3}CO{O}^{-}+H^{+};K_a=1.5\times 10-5H^{+}+C{N}^{-}HCN;\frac{1}{K_a}=\frac{1}{4.5\times {10}^{-10}}{K}_{a}forC{N}^{-}+C{H}_{3}COOH\iff C{H}_{3}CO{O}^{-}+HCNis\frac{1.5\times {10}^{-5}}{4.5\times {10}^{-10}}=\frac{1}{3}\times {10}^5=3\times {10}^4$