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Basics of Organic Chemistry question

2022 · 25 Jun · Shift 2 · Q9
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Basics of Organic Chemistry question

2022 · 25 Jun · Shift 2 · Q9

JEE MainChemistryBasics of Organic ChemistryMCQ+4 / −1
Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : A mixture contains benzoic acid and napthalene. The pure benzoic acid can be separated out by the use of benzene. Reason R : Benzoic acid is soluble in hot water. In the light of the above statements, choose the most appropriate answer from the options given below.
  1. A
    Both A and R are true and R is the correct explanation of A.
  2. B
    Both A and R are true but R is NOT the correct explanation of A.
  3. C
    A is true but R is false.
  4. D
    A is false but R is true.
View written solutionFree

Correct answer: D

  1. Understand the assertion

    The mixture contains benzoic acid and naphthalene.

    We need to check whether pure benzoic acid can be separated by using benzene.

  2. Check solubility behavior in benzene

    • Naphthalene is a non-polar aromatic compound, so it is readily soluble in benzene.
    • Benzoic acid is much less soluble in benzene compared to naphthalene and is generally separated better by hot water recrystallization, not by simply using benzene to obtain pure benzoic acid.

    If benzene is used, typically naphthalene dissolves, leaving benzoic acid behind. Hence benzoic acid can indeed be separated from the mixture by treatment with benzene.

    So, Assertion A is true.

  3. Check the reason

    Reason states: Benzoic acid is soluble in hot water.

    This is true. Benzoic acid is sparingly soluble in cold water but much more soluble in hot water.

  4. Check whether R explains A

    The assertion talks about separation by the use of benzene.

    The reason talks about solubility of benzoic acid in hot water.

    Since the separation mentioned in A is based on benzene, the statement about solubility in hot water does not explain that assertion.

  5. Conclusion

    • Assertion A = True
    • Reason R = True
    • R is not the correct explanation of A

    Therefore, the correct option is:

    B\boxed{\text{B}}B​

  6. Comparison with stored answer

    Stored correct answer is D.

    My derived answer is B. Hence, I disagree with the stored answer.

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