Match List I with List II
|
List I Given pair of organic compounds can be distinguished by |
List II Tests |
| 1. Ethanal/ Propanal | I. Sodium Hydrogen carbonate test |
| 2. Ethanol/ Ethanoic acid | II. Fehling's Test |
| 3. Butanal/ Butan-2-one | III. Tollen's Test |
| 4. Benzaldehyde/ Ethanal | IV. Iodoform Test |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 1 – IV, 2 – I, 3 – III, 4 – II
Two compounds are told apart by a test that only one of them answers. The key structural features are: a \( \ce{CH3CO} \)– group (iodoform test), a –COOH group (\( \ce{NaHCO3} \) test), an aldehyde group (Tollens’ test), and an aliphatic aldehyde group (Fehling’s test, which aromatic aldehydes do not answer).
1. Ethanal/Propanal — This matches IV. Iodoform Test. Both are aldehydes, but only ethanal has a \( \ce{CH3CO} \)– group and gives a yellow precipitate of iodoform:
\( \displaystyle \ce{CH3CHO + 3I2 + 4NaOH -> CHI3 v + HCOONa + 3NaI + 3H2O} \)
2. Ethanol/Ethanoic acid — This matches I. Sodium Hydrogen carbonate test. Only the acid gives brisk effervescence of \( \ce{CO2} \):
\( \displaystyle \ce{CH3COOH + NaHCO3 -> CH3COONa + H2O + CO2 ^} \)
3. Butanal/Butan-2-one — This matches III. Tollen’s Test. Only the aldehyde reduces Tollens’ reagent and gives a silver mirror; the ketone does not:
\( \displaystyle \ce{RCHO + 2[Ag(NH3)2]+ + 3OH- -> RCOO- + 2Ag v + 2H2O + 4NH3} \)
4. Benzaldehyde/Ethanal — This matches II. Fehling’s Test. Both are aldehydes and both give the Tollens’ test, but only the aliphatic ethanal gives the red-brown precipitate of \( \ce{Cu2O} \) with Fehling’s solution:
\( \displaystyle \ce{RCHO + 2Cu^2+ + 5OH- -> RCOO- + Cu2O v + 3H2O} \)
Shortcut: The pair 1-IV appears in Options (1) and (3), and 3-III then leaves only Option (3).