Question

Which is the stronger acid in each pair? (a) \(\mathrm{CH}_{3} \mathrm{COOH}\) or $\mathrm{CH}_{3} \mathrm{SO}_{3} \mathrm{H}$ (b)

Short answer

Answer: (a) \(\mathrm{CH}_{3} \mathrm{SO}_{3}\mathrm{H}\) is the stronger acid, and (b) \(\mathrm{H}_{2} \mathrm{SO}_{3}\) is the stronger acid.

Step-by-step solution

Identify the conjugate bases

In order to determine which is the stronger acid, first identify the conjugate base of each acid by removing one hydrogen ion (H+) from the formula of each acid. (a) Conjugate base of \(\mathrm{CH}_{3} \mathrm{COOH}\): \(\mathrm{CH}_{3} \mathrm{COO}^{-}\) Conjugate base of \(\mathrm{CH}_{3} \mathrm{SO}_{3}\mathrm{H}\): \(\mathrm{CH}_{3} \mathrm{SO}_{3}^{-}\) (b) Conjugate base of \(\mathrm{H}_{2} \mathrm{CO}_{3}\): \(\mathrm{HCO}_{3}^{-}\) Conjugate base of \(\mathrm{H}_{2} \mathrm{SO}_{3}\): \(\mathrm{HSO}_{3}^{-}\)

Analyze stability of conjugate bases

Next, analyze the stability of each conjugate base, taking into consideration factors such as resonance structures, inductive effects, and electronegativity. (a) \(\mathrm{CH}_{3} \mathrm{COO}^{-}\) has resonance structures due to the double bond in the \(\mathrm{COO}^{-}\) group, which delocalizes the negative charge, making it more stable. \(\mathrm{CH}_{3} \mathrm{SO}_{3}^{-}\) has resonance structures due to the double bonds in the \(\mathrm{SO}_{3}^{-}\) group, which more effectively delocalizes the negative charge, making it more stable than \(\mathrm{CH}_{3} \mathrm{COO}^{-}\). (b) \(\mathrm{HCO}_{3}^{-}\) has resonance structures due to the double bond in the \(\mathrm{CO}_{3}^{-}\) group, which delocalizes the negative charge, making it more stable. \(\mathrm{HSO}_{3}^{-}\) has resonance structures due to the double bonds in the \(\mathrm{SO}_{3}^{-}\) group, which more effectively delocalizes the negative charge, making it more stable than \(\mathrm{HCO}_{3}^{-}\).

Determine the stronger acid

Based on the stability of the conjugate bases, we can now determine which acid is stronger. Remember, the more stable the conjugate base, the stronger the acid. (a) Since \(\mathrm{CH}_{3} \mathrm{SO}_{3}^{-}\) is more stable than \(\mathrm{CH}_{3} \mathrm{COO}^{-}\), \(\mathrm{CH}_{3} \mathrm{SO}_{3}\mathrm{H}\) is the stronger acid. (b) Since \(\mathrm{HSO}_{3}^{-}\) is more stable than \(\mathrm{HCO}_{3}^{-}\), \(\mathrm{H}_{2} \mathrm{SO}_{3}\) is the stronger acid.