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MCQEasyJEE 2026Volumetric Analysis (Titrations)

JEE Chemistry 2026 Question with Solution

Identify the correct statements:

A. Hydrated salts can be used as primary standard.

B. Primary standard should not undergo any reaction with air.

C. Reactions of primary standard with another substance should be instantaneous and stoichiometric.

D. Primary standard should not be soluble in water.

E. Primary standard should have low relative molar mass.

Choose the correct answer from the options given below:

  • A

    A, B and C Only

  • B

    A, B, C and E Only

  • C

    A, B and E Only

  • D

    D and E Only

Answer

Correct answer:C

Step-by-step solution

Standard Method

Given: Statements about the properties of a primary standard are given.

Find: Which statements are correct.

Step 1: Analyze statement A. Hydrated salts can be used as primary standards provided they have a definite and stable composition. Therefore, statement A is correct.

Step 2: Analyze statement B. A primary standard must be chemically stable and should not react with air, for example it should not absorb moisture or CO2\mathrm{CO_2}. Therefore, statement B is correct.

Step 3: Analyze statement C. Reactions involving primary standards should be stoichiometric, but they need not always be instantaneous. Therefore, statement C is incorrect.

Step 4: Analyze statement D. A primary standard must be readily soluble in water so that its solution can be prepared accurately. Therefore, statement D is incorrect.

Step 5: Analyze statement E. According to the provided solution, primary standards should preferably have low relative molar mass so that weighing errors are minimized. Therefore, statement E is correct.

Conclusion: The correct statements are A, B and E only.

Therefore, the correct option is C.

Statement-wise Explanation

Given: A list of five statements about primary standards.

Find: The combination containing only the correct statements.

A good primary standard must be pure, stable in air, soluble in water, and react stoichiometrically with the titrant.

  • A is correct because some hydrated salts can serve as primary standards if their composition remains fixed and stable.
  • B is correct because reaction with air changes composition and affects accurate weighing.
  • C is incorrect because stoichiometric reaction is required, but instantaneous reaction is not an essential condition in every case.
  • D is incorrect because a primary standard should be soluble in water, not insoluble.
  • E is taken as correct as per the provided solution.

Hence, only A, B and E are correct, so the correct option is C.

Common mistakes

  • Treating instantaneous reaction as a compulsory condition for a primary standard. This is wrong because the essential requirement is a stoichiometric reaction. Do not reject a statement only because the reaction may not be instantaneous.

  • Assuming a primary standard should be insoluble in water. This is wrong because accurate solution preparation requires sufficient solubility. Instead, remember that good water solubility is desirable.

  • Ignoring reaction with air such as absorption of moisture or CO2\mathrm{CO_2}. This is wrong because such reactions change the composition of the weighed sample. Instead, a primary standard should remain stable in air.

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