Question

In each equilibrium, label the stronger acid, the stronger base, the weaker acid, and the weaker base. Also estimate the position of each equilibrium. (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}+\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{CH} \rightleftharpoons \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}+\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{C}^{-}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}+\mathrm{HCl} \rightleftharpoons \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}+\mathrm{Cl}^{-}\) (c) \(\mathrm{CH}_{3} \mathrm{COOH}+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-} \rightleftharpoons \mathrm{CH}_{3} \mathrm{COO}^{-}+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\)

Short answer

Question: In each of the given equilibrium reactions, label the stronger acid, stronger base, weaker acid, and weaker base. Also, estimate the position of the equilibrium. (a) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}+\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{CH} \rightleftharpoons \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}+\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{C}^{-}$ Answer: In this reaction, the stronger acid is $\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{CH}$, the weaker acid is $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}$, the stronger base is $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}$, and the weaker base is $\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{C}^{-}$. The position of the equilibrium lies to the right. (b) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}+\mathrm{HCl} \rightleftharpoons \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}+\mathrm{Cl}^{-}$ Answer: In this reaction, the stronger acid is $\mathrm{HCl}$, the weaker acid is $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}$, the stronger base is $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}$, and the weaker base is $\mathrm{Cl}^{-}$. The position of the equilibrium lies to the right. (c) $\mathrm{CH}_{3} \mathrm{COOH}+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-} \rightleftharpoons \mathrm{CH}_{3} \mathrm{COO}^{-}+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}$ Answer: In this reaction, the stronger acid is $\mathrm{CH}_{3} \mathrm{COOH}$, the weaker acid is $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}$, the stronger base is $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}$, and the weaker base is $\mathrm{CH}_{3} \mathrm{COO}^{-}$. The position of the equilibrium lies to the right.

Step-by-step solution

Identify the conjugate acid-base pairs

In this reaction, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}\) is the conjugate base of \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\), and \(\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{C}^{-}\) is the conjugate base of \(\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{CH}\).

Compare the strength of the acids

Generally, a terminal alkyne like \(\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{CH}\) is a stronger acid than an alcohol like \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\). Therefore, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) is the weaker acid.

Compare the strength of the bases

Correspondingly, the conjugate base of the stronger acid (\(\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{C}^{-}\)) is weaker than the conjugate base of the weaker acid (\(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}\)).

Determine the position of the equilibrium

The equilibrium will favour the formation of the weaker acid and weaker base. In this case, it will lie to the right, producing more \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) and \(\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{C}^{-}\). (b) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}+\mathrm{HCl} \rightleftharpoons \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}+\mathrm{Cl}^{-}$

Identify the conjugate acid-base pairs

In this reaction, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}\) is the conjugate base of \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\), and \(\mathrm{Cl}^{-}\) is the conjugate base of \(\mathrm{HCl}\).

Compare the strength of the acids

\(\mathrm{HCl}\) is a strong acid, much stronger than \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\). Therefore, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) is the weaker acid.

Compare the strength of the bases

Correspondingly, the conjugate base of the stronger acid (\(\mathrm{Cl}^{-}\)) is weaker than the conjugate base of the weaker acid (\(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}\)).

Determine the position of the equilibrium

The equilibrium will favour the formation of the weaker acid and weaker base. In this case, it will lie to the right, producing more \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) and \(\mathrm{Cl}^{-}\). (c) $\mathrm{CH}_{3} \mathrm{COOH}+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-} \rightleftharpoons \mathrm{CH}_{3} \mathrm{COO}^{-}+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}$

Identify the conjugate acid-base pairs

In this reaction, \(\mathrm{CH}_{3} \mathrm{COOH}\) is the conjugate acid of \(\mathrm{CH}_{3} \mathrm{COO}^{-}\), and \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) is the conjugate acid of \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}\).

Compare the strength of the acids

Both \(\mathrm{CH}_{3} \mathrm{COOH}\) (acetic acid) and \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (ethanol) are weak acids, but acetic acid is generally a stronger acid than ethanol. Therefore, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) is the weaker acid.

Compare the strength of the bases

Correspondingly, the conjugate base of the stronger acid (\(\mathrm{CH}_{3} \mathrm{COO}^{-}\)) is weaker than the conjugate base of the weaker acid (\(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}\)).

Determine the position of the equilibrium

The equilibrium will favour the formation of the weaker acid and weaker base. In this case, it will lie to the right, producing more \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) and \(\mathrm{CH}_{3} \mathrm{COO}^{-}\).