FSC Chemistry: Carboxylic acids, questions with answers

Answer: C. LiAlH₄

LiAlH₄ is a strong enough reducing agent to reduce carboxylic acids all the way to primary alcohols.

Answer: A. Amide

Amides are the least reactive carboxylic acid derivative toward nucleophilic acyl substitution, due to strong resonance delocalization of the N lone pair into the carbonyl.

Answer: A. Carboxylic acids > Phenols > Alcohols

Carboxylate ions are best resonance-stabilized, phenoxide ions less so, and alkoxide ions not at all — so acidity order is carboxylic acids > phenols > alcohols.

Answer: B. CH₃CH₂OH

LiAlH₄ reduces carboxylic acids all the way to primary alcohols: CH₃COOH → CH₃CH₂OH.

Answer: C. 4

Butanoic acid has 4 distinct proton environments: the terminal CH₃, the middle CH₂, the CH₂ next to –COOH, and the –COOH proton itself.

Answer: D. Saponification

Alkaline hydrolysis of an ester into an alcohol and a carboxylate salt is called saponification (soap-making reaction).

CH₂ClCOOH (chloroacetic acid) is more acidic than CH₃COOH (acetic acid). The electronegative chlorine atom exerts an electron-withdrawing inductive (−I) effect, which pulls electron density away from the carboxylate group, stabilizing the conjugate base (CH₂ClCOO⁻) by dispersing its negative charge. This greater stabilization of the conjugate base makes CH₂ClCOOH dissociate more readily (stronger acid) compared to CH₃COOH, where the methyl group's weak +I effect (electron donating) slightly destabilizes the conjugate base instead.

Grignard reagent (CH₃MgBr) reacts with dry ice (solid CO₂) — the carbanion attacks the electrophilic carbon of CO₂ to form a magnesium carboxylate salt: CH₃MgBr + CO₂ → CH₃COOMgBr. This salt is then hydrolyzed with dilute acid (H₃O⁺) to give acetic acid, CH₃COOH.