Question

Which of the following is correct with respect to the acidity of benzene sulphonic acid and benzoic acid?

• A. Benzene sulphonic acid > Benzoic acid
• B. Benzene sulphonic acid < Benzoic acid
• C. Benzene sulphonic acid = Benzoic acid
• D. None of the above

Answer 1

Answer: (A)

Benzene sulphonic acid > Benzoic acid

The conjugate base of benzene sulphonic acid has greater resonance stabilization than benzoate ion, hence benzene sulphonic acid is a stronger acid than benzoic acid. $PhS{O}_3^{-}$ has three equivalent resonance structure, so more stable. but $PhCO{O}^{-}$ has only two equivalent resonance structure, so less stable.