Question

Consider the reaction: $HCN+C_2{H}_3{O}_2^{-}\rightleftharpoons C{N}^{-}+H{C}_2{H}_3{O}_2$
The $p{K}_a$ of HCN is 9.31 and the $p{K}_a$ of $H{C}_2{H}_3{O}_2$ is 4.74. If the reaction is initiated under standard conditions, what is true about the relative concentrations of HCN and $H{C}_2{H}_3{O}_2$ once the reaction reaches equilibrium?

• A. There is less HCN than $H{C}_2{H}_3{O}_2$
• B. There are equal amounts of HCN and $H{C}_2{H}_3{O}_2$
• C. There is more HCN than $H{C}_2{H}_3{O}_2$
• D. More information is needed in order to know which acid is dominant

Answer 1

The correct option is B There are equal amounts of HCN and $H{C}_2{H}_3{O}_2$

Given equation $HCN+C_2{H}_3{O}_2^{-}\rightleftharpoons C{N}^{-}+H{C}_3{H}_3{O}_2$ .

There are equal amounts of $HCN$ and $H{C}_3{H}_3{O}_2$ at equilibrium, because of equilibrium forward reaction is equal to backward reaction.