O Levels Chemistry (5070)•5070/11/M/J/20
Explanation
Carboxylic acids react with Mg, aq NaOH, and EtOH Steps:
- Identify functional groups that chemically react with all three reagents: Mg (active metal), aq NaOH (base), and EtOH (alcohol).
- -COOH reacts with Mg to form salt and H₂ (2RCOOH + Mg → (RCOO)₂Mg + H₂), with aq NaOH to form carboxylate (RCOOH + NaOH → RCOONa + H₂O), and with EtOH to form ester (RCOOH + CH₃CH₂OH → RCOOCH₂CH₃ + H₂O, acid-catalyzed).
- Other groups fail to react with at least one reagent, eliminating them.
- Compound T must contain -COOH to exhibit all reactions.
Why C is correct:
- Carboxylic acids are sufficiently acidic (pKa ~4-5) to liberate H₂ from Mg, neutralize NaOH per acid-base reaction, and undergo Fischer esterification with EtOH.
Why the others are wrong:
- A. Alcohols (pKa ~15-18) do not react with Mg or aq NaOH.
- B. Terminal alkynes (pKa ~25) do not react with aq NaOH or Mg.
- D. Esters hydrolyze with aq NaOH but inert to Mg and EtOH.
Final answer: C
Topic: Carboxylic acids
Practice more O Levels Chemistry (5070) questions on mMCQ.me