Which acid is the strongest?
Correct answer: C. Trichloroethanoic acid
- A. Ethanoic acid
- B. Propanoic acid
- C. Trichloroethanoic acid
- D. Butanoic acid
Explanation
Three electronegative chlorine atoms withdraw electron density powerfully and stabilise the carboxylate ion, so trichloroethanoic acid is a strong acid, comparable in strength to some mineral acids. Among the unsubstituted acids, strength falls slightly as the alkyl chain lengthens because alkyl groups release electron density. This is why methanoic acid is the strongest of the simple aliphatic acids.
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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.
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