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MCQEasyJEE 2025Carboxylic Acids

JEE Chemistry 2025 Question with Solution

Mixture of 1 g1 \, \text{g} each of chlorobenzene, aniline and benzoic acid is dissolved in 50 mL50 \, \text{mL} ethyl acetate and placed in a separating funnel, 5 M5 \, \text{M} NaOH (30 mL30 \, \text{mL}) was added in the same funnel. The funnel was shaken vigorously and then kept aside. The ethyl acetate layer in the funnel contains :

  • A

    benzoic acid

  • B

    benzoic acid and aniline

  • C

    benzoic acid and chlorobenzene

  • D

    chlorobenzene and aniline

Answer

Correct answer:D

Step-by-step solution

Standard Method

Given: A mixture containing chlorobenzene, aniline and benzoic acid is dissolved in ethyl acetate. Aqueous 5 M5 \, \text{M} NaOH is added in a separating funnel.

Find: Which compounds remain in the ethyl acetate layer after shaking and separation.

Benzoic acid is an acidic compound, so it reacts with NaOH to form the water-soluble salt sodium benzoate.

C6H5COOH+NaOH→C6H5COONa+H2O\text{C}_6\text{H}_5\text{COOH} + \text{NaOH} \rightarrow \text{C}_6\text{H}_5\text{COONa} + \text{H}_2\text{O}

Because sodium benzoate is ionic, it preferentially goes into the aqueous NaOH layer rather than the organic ethyl acetate layer.

Chlorobenzene does not react with NaOH under these conditions, and aniline, being a weak base, also does not form a water-soluble salt with NaOH. Therefore both remain mainly in the organic ethyl acetate layer.

Therefore, the ethyl acetate layer contains chlorobenzene and aniline. The correct option is D.

Layer Separation Logic

Given: Chlorobenzene, aniline and benzoic acid are present in ethyl acetate. Aqueous NaOH is added.

Find: The composition of the organic layer after extraction.

  1. Chlorobenzene is neutral and non-polar. It is soluble in the organic solvent and does not react with NaOH.
  2. Aniline is a weak organic base. It reacts with acids, not with NaOH, so it remains largely in molecular form and stays in the organic layer.
  3. Benzoic acid is a carboxylic acid and reacts with NaOH to form sodium benzoate, which is water-soluble.

Thus, after shaking the separating funnel:

  • Aqueous layer: NaOH solution + sodium benzoate
  • Organic ethyl acetate layer: chlorobenzene + aniline

Hence, the correct answer is D.

Common mistakes

  • Assuming aniline reacts with NaOH. This is incorrect because aniline is itself a weak base, so NaOH does not convert it into a water-soluble salt. Instead, aniline remains mostly in the organic layer.

  • Forgetting that benzoic acid becomes sodium benzoate in basic medium. This is wrong because the salt is ionic and prefers the aqueous layer. Always check whether an acid or base is converted into a water-soluble salt during extraction.

  • Judging separation only by original solubility and ignoring chemical reaction. This leads to error because extraction here depends on both solubility and acid-base reaction. First identify which component is transformed into an ionic species.

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