Which of the following is the strongest acid ?
Correct answer: B. Formic acid
- A. Water
- B. Formic acid
- C. Acetic acid
- D. Propanoic acid
Explanation
Formic acid is the strongest of these weak acids because the alkyl groups in acetic and propanoic acids donate electron density toward the carboxyl group, reducing ionisation. Water is much weaker because its O-H bond ionises far less readily in water. A common mistake is choosing acetic acid because it is a familiar acid, while overlooking the electron-donating effect of its methyl group.
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About Reactivity of Carboxylic Acids
Carboxylic acids show acidic behaviour because their carboxylate ions are resonance-stabilised, and electron-withdrawing groups can change their strength. Reactions include neutralisation, esterification, formation of acid chlorides and amides, reduction, decarboxylation and substitution at the acyl carbon, which differs from the reactions of phenols.
Practise Carboxylic Acids
550 free Carboxylic Acids MCQs from Chemistry, each with the correct answer and an explanation. Unlimited attempts, no account needed.
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