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A Levels Chemistry (9701)•9701/13/O/N/18
Question 29 from 9701/13/O/N/18

Explanation

Saponification of diester with excess NaOH

Steps:

  • Recognize the compound as a diester with two -COOR groups.
  • Alkaline hydrolysis cleaves each ester bond using OH⁻ from NaOH.
  • Each ester yields a carboxylate salt (-COONa) and an alcohol (ROH).
  • Excess NaOH ensures complete conversion to salts, not acids.

Why C is correct:

  • C depicts the disodium dicarboxylate and two alcohol molecules, matching the saponification formula: RCOOR' + NaOH → RCOONa + R'OH for both esters.

Why the others are wrong:

  • A shows the free diacid, but excess base forms salts, not H⁺-protonated acids.
  • B indicates mono-hydrolysis product, ignoring excess NaOH for full reaction.
  • D includes unchanged ester or wrong byproducts, violating complete hydrolysis.

Final answer: C

Topic: Carboxylic acids and derivatives

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