AIIMS 2006 Chemistry Standard Solutions Assertion Reason Question

To tackle the assertion and reason provided in the question, we need to evaluate the truthfulness of each statement and their relationship.

Assertion: K₂Cr₂O₇ is used as a primary standard in volumetric analysis.

Explanation:

• Potassium dichromate (K₂Cr₂O₇) is indeed utilized as a primary standard in volumetric analysis. A primary standard is a reagent that is pure, stable, and has a known and high molar mass, which allows for accurate and reproducible results in titrations. K₂Cr₂O₇ meets these criteria because:
  • It is stable under normal conditions.
  • It is available in a pure form.
  • Its molar mass (approximately 294.19 g/mol) allows for precise calculations in stoichiometric reactions.

Reason: It has a good solubility in water.

Explanation:

• While K₂Cr₂O₇ is soluble in water (which is indeed greater than 1 g per 100 mL), this characteristic alone does not qualify it as a primary standard. The key factors that make a substance a suitable primary standard are its purity, stability, and the ability to form a consistent and reliable solution, rather than just solubility. Therefore, while the reason is true, it is not the correct explanation for why K₂Cr₂O₇ is used as a primary standard.

Conclusion:

With the assessment of both the assertion and the reason, we find that:

• Assertion is true: K₂Cr₂O₇ is used as a primary standard.
• Reason is true but does not explain the assertion: The solubility of K₂Cr₂O₇ is a property but does not justify its status as a primary standard in volumetric analysis.

Thus, the correct answer is C) if assertion is true, but reason is false.

Clarification of Other Options:

• Option A: Incorrect because, while both statements are true, the reason does not correctly explain the assertion.
• Option B: Incorrect since both statements are true, but the reason fails to provide the correct explanation for the assertion.
• Option D: Incorrect because the assertion is true; K₂Cr₂O₇ is indeed used as a primary standard.

Summary:

In summary, while both the assertion and reason are true independently, the reason does not serve as a valid explanation for the assertion. Therefore, the correct choice is C.