A Levels Chemistry (9701)•9701/13/M/J/25
Explanation
Neutralization of dicarboxylic acid forms disodium salt
Steps:
- Butenedioic acid is HOOC-CH=CH-COOH, a dicarboxylic acid with two ionizable protons.
- NaOH(aq) acts as a base, deprotonating carboxylic acids via acid-base reaction.
- Excess NaOH ensures both COOH groups react completely, forming the dianion.
- The organic product is the butenedioate ion, NaOOC-CH=CH-COONa.
Why A is correct:
- A represents the disodium butenedioate, matching the full deprotonation of both carboxyl groups per acid-base neutralization (HA + OH⁻ → A⁻ + H₂O, doubled for diacid).
Why the others are wrong:
- B is the monosodium salt, incomplete reaction due to insufficient base.
- C shows hydration across the double bond, not occurring under basic conditions.
- D is the anhydride form, which requires dehydration, not applicable here.
Final answer: A
Topic: Carboxylic acids and derivatives
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