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MCQEasyJEE 2023Detection of Elements in Organics

JEE Chemistry 2023 Question with Solution

Given below are two statements :

Statement I : Sulphanilic acid gives esterification test for carboxyl group.

Statement II : Sulphanilic acid gives red colour in Lassaigne's test for extra element detection.

In the light of the above statements, choose the most appropriate answer from the options given below :

  • A

    Statement I is correct but Statement II is incorrect.

  • B

    Both Statement I and Statement II are incorrect.

  • C

    Both Statement I and Statement II are correct.

  • D

    Statement I is incorrect but Statement II is correct.

Answer

Correct answer:D

Step-by-step solution

Standard Method

Given: Two statements about sulphanilic acid are to be checked.

Find: Which option correctly identifies the truth values of Statement I and Statement II.

Statement I: Sulphanilic acid contains an amino group and a sulfonic acid group, not a carboxyl group. Therefore it does not give the esterification test for a carboxyl group.

−NH2,  −SO3H≠−COOH-\text{NH}_2, \; -\text{SO}_3\text{H} \neq -\text{COOH}

So, Statement I is incorrect.

Statement II: Lassaigne's test is used for detection of extra elements such as nitrogen and sulfur in an organic compound. Sulphanilic acid contains sulfur and nitrogen, and the test can give a red colour due to formation of ferric thiocyanate.

Fe3++SCN−→ferric thiocyanate complex\text{Fe}^{3+} + \text{SCN}^- \rightarrow \text{ferric thiocyanate complex}

So, Statement II is correct.

Therefore, the correct option is D.

Common mistakes

  • Assuming sulphanilic acid contains a carboxyl group because it is an acid is incorrect. It contains a sulfonic acid group, so identify the functional group correctly before applying esterification logic.

  • Confusing carboxylic acid tests with sulfonic acid behavior is wrong. Esterification test is characteristic of the carboxyl group, not of every acidic organic compound.

  • Thinking Lassaigne's test checks only one extra element is incorrect. It is used to detect elements like nitrogen and sulfur, so a compound containing these can support the relevant colour test.

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