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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3g2052

Which of the following statements are correct?

  1. AMethanesulfonic acid is a much stronger acid than ethanoic acid because the negative charge of the sulfonate ion is delocalised over three oxygen atoms.
  2. BTrifluoroethanoic acid is a stronger acid than ethanoic acid because of the -I effect of the three fluorine atoms.
  3. CPhenol is a stronger acid than benzenesulfonic acid.
  4. DBenzenesulfonic acid is a stronger acid than benzoic acid.

Answer: A, B, D

Sulfonic acids (pKa below 0) are stronger than carboxylic acids (4-5) because the sulfonate anion shares its charge over three oxygens. CF3COOH (pKa about 0.5) is stronger than CH3COOH (4.76) owing to the strong -I effect of fluorine. Phenol (pKa 10.0) is far weaker than benzenesulfonic acid, so statement 3 is false.
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