Question

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

Hint:

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

Answer 1

The Correct Option is C

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

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

Step 3: Analyze Statement C.
Although reactions involving primary standards should be stoichiometric, 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 to prepare solutions accurately. Hence, Statement D is incorrect.

Step 5: Analyze Statement E.
Primary standards should preferably have a low relative molar mass so that weighing errors are minimized. Hence, Statement E is correct.

Step 6: Conclusion.
Correct statements are A, B and E only.

Final Answer: \[ \boxed{\text{A, B and E Only}} \]