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Difficulty: EasyAlkanals and Alkanones: Oxidation, Reduction, and Distinction Tests

Match each chemical reaction or test involving carbonyl compounds in Column A with its corresponding characteristic visual outcome in Column B.

  • Warming ethanal with Fehling's solutionFormation of a brick-red precipitate
  • Warming propanone with Tollen's reagentNo visible reaction occurs
  • Warming propanal with acidified potassium tetraoxomanganate(VII) solutionDecolorization of the purple solution
  • Warming propanone with iodine in sodium hydroxide solutionFormation of a pale yellow precipitate

Answer

Warming ethanal with Fehling's solution yields a brick-red precipitate; warming propanone with Tollen's reagent yields no visible reaction; warming propanal with acidified KMnO4KMnO_4 causes decolorization of the purple solution; and warming propanone with iodine in sodium hydroxide solution produces a pale yellow precipitate.
Alkanals (ethanal and propanal) are reducing agents due to the carbonyl hydrogen atom; thus, ethanal reduces Fehling's solution to a brick-red copper(I) oxide precipitate, and propanal reduces purple acidified KMnO4KMnO_4 to a colorless Mn2+Mn^{2+} solution. Alkanones (propanone) lack this hydrogen atom, so propanone shows no reaction with Tollen's reagent. However, because propanone has a CH3CO−CH_3CO- group, it responds to the triiodomethane test by forming a pale yellow precipitate.

Step-by-Step Solution

1
Analyze the oxidation reactions of alkanals.
Ethanal reduces Fehling's solution to form brick-red Cu2OCu_2O, while propanal reduces acidified KMnO4KMnO_4, turning the purple solution colorless.
Alkanals possess a hydrogen atom bonded to the carbonyl carbon, enabling easy oxidation by mild and strong oxidizing agents.
2
Analyze the oxidation behavior of alkanones.
Propanone yields no visible reaction with Tollen's reagent.
Alkanones lack a hydrogen atom on the carbonyl carbon and are resistant to oxidation by mild oxidizing agents.
3
Identify the triiodomethane (iodoform) test reaction.
Propanone forms a pale yellow precipitate of triiodomethane (CHI3CHI_3).
Propanone contains the CH3C=OCH_3C=O group required for a positive triiodomethane test.

Key Concept

Distinction tests and oxidation properties of alkanals and alkanones
Estimated Time:1m 0s
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Topics

Alkanals and Alkanones: Oxidation, Reduction, and Distinction Tests

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