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    Question

    Which of the following does not give effervescence with

    sodium carbonate?
    A Acetic acid Correct Answer Incorrect Answer
    B Phenol Correct Answer Incorrect Answer
    C Formic acid Correct Answer Incorrect Answer
    D Citric acid Correct Answer Incorrect Answer

    Solution

    Effervescence with sodium carbonate (Na₂CO₃) is due to the release of carbon dioxide (CO₂) gas when it reacts with an acid: 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂↑ This reaction occurs only if the compound has acidic hydrogen strong enough to liberate CO₂ from carbonate. Phenol does not give effervescence because: It is a very weak acid and does not react with carbonates or bicarbonates to release CO₂. It cannot liberate CO₂ gas due to the stability of the phenoxide ion and weak acidity.

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