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Practical Organic Chemistry question

2019 · 9 Apr · Shift 1 · Q14
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Practical Organic Chemistry question

2019 · 9 Apr · Shift 1 · Q14

JEE MainChemistryPractical Organic ChemistryMCQ+4 / −1
The organic compound that gives following qualitative analysis is :

Test Inference
(a) Dil. HCl Insoluble
(b) NaOH solution soluble
(c) Br2/water Decolourization
  1. A
    JEE Main 2019 (Online) 9th April Morning Slot Chemistry - Practical Organic Chemistry Question 77 English Option 1
  2. B
    JEE Main 2019 (Online) 9th April Morning Slot Chemistry - Practical Organic Chemistry Question 77 English Option 2
  3. C
    JEE Main 2019 (Online) 9th April Morning Slot Chemistry - Practical Organic Chemistry Question 77 English Option 3
  4. D
    JEE Main 2019 (Online) 9th April Morning Slot Chemistry - Practical Organic Chemistry Question 77 English Option 4
View written solutionFree

Correct answer: A

  1. Interpret the qualitative tests

    We are given:

    • Dilute HCl: insoluble
    • NaOH solution: soluble
    • Br2/H2O\mathrm{Br_2/H_2O}Br2​/H2​O: decolourization

  2. Meaning of solubility in dilute HCl

    Organic compounds soluble in dilute HCl are generally basic, such as amines, because they form water-soluble ammonium salts.

    Since the compound is insoluble in dilute HCl, it is not a basic compound like an amine.

  3. Meaning of solubility in NaOH

    Organic compounds soluble in NaOH are usually acidic enough to form salts, such as:

    • carboxylic acids
    • phenols

    So the compound must contain an acidic functional group.

  4. Meaning of bromine water decolourization

    Decolourization of bromine water suggests either:

    • unsaturation (C=C\mathrm{C=C}C=C or C≡C\mathrm{C\equiv C}C≡C), or
    • a strongly activated aromatic ring such as phenol/aniline undergoing electrophilic substitution.

  5. Combine all observations

    • Not basic ⇒\Rightarrow⇒ not an amine
    • Soluble in NaOH ⇒\Rightarrow⇒ acidic compound
    • Decolourizes bromine water ⇒\Rightarrow⇒ most consistent with phenol

    A phenol is:

    • insoluble in dilute HCl
    • soluble in NaOH due to formation of sodium phenoxide
    • decolourizes bromine water due to formation of tribromophenol

  6. Conclusion

    Therefore, the compound must be the phenolic compound, which corresponds to Option A.

A\boxed{A}A​

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