AIIMS 2006 Chemistry Titrations Assertion Reason Question

To understand the question about iodometric titration, let's analyze both the assertion and the reason provided.

Assertion

Assertion: In the iodometric titration, starch is used as an indicator.

This assertion is true. In iodometric titrations, starch is indeed employed as an indicator, particularly in the titration of iodine. When iodine is present in solution, it forms a blue complex with starch, which allows for a visual identification of the endpoint of the titration. The blue color disappears when all iodine has reacted, indicating the endpoint.

Reason

Reason: Starch is a polysaccharide.

This reason is also true. Starch is a complex carbohydrate made up of numerous glucose units linked by glycosidic bonds, qualifying it as a polysaccharide.

Correct Answer Explanation

The correct answer is B: both assertion and reason are true, but the reason is not the correct explanation of the assertion.

While it is correct that starch is a polysaccharide, the reason does not explain why starch serves as an indicator in iodometric titration. The function of starch as an indicator is due to its ability to form a colored complex with iodine, not merely because it is a polysaccharide.

Why Other Options Are Incorrect

• Option A: This option states that both assertion and reason are true, and the reason is a correct explanation. This is incorrect because, although both statements are true, the reason does not justify the assertion adequately.

• Option C: This option states that the assertion is true, but the reason is false. This is incorrect because both the assertion and reason are true.

• Option D: This option states that both assertion and reason are false statements. This is incorrect as both statements are indeed true.

Key Concept

In summary, the use of starch in iodometric titration is related to its interaction with iodine to form a blue complex, which serves as a visual endpoint indicator. The mere fact that starch is a polysaccharide does not directly explain its role as an indicator.

Conclusion

Thus, the correct answer is B since both statements are true, but the reason provided does not explain the assertion about the use of starch in iodometric titration. Understanding the role of indicators and the chemistry behind titrations is crucial for mastering analytical chemistry concepts in NEET/JEE exams.