Question

Identify the incorrect statements regarding primary standard of titrimetric analysis
(A) It should be purely available in dry form.
(B) It should not undergo chemical change in air.
(C) It should be hygroscopic and should react with another chemical instantaneously and stoichiometrically.
(D) It should be readily soluble in water.
(E) KMnO4 & NaOH can be used as primary standard.
Choose the correct answer from the options given below :

• (C) and (D) only
• (B) and (E) only
• (A) and (B) only
• (C) and (E) only

Answer 1

The Correct Option is D

To identify the inaccurate assertions concerning the primary standard in titrimetric analysis, each option will be assessed:

1. (A) It must exist in a dry state: This statement is accurate. Primary standards require high purity and stability, typically in a dry form, to guarantee precise measurements.
2. (B) It must remain chemically unchanged in the atmosphere: This assertion is also accurate. Primary standards must be atmospherically stable to prevent reactions with humidity or gases, thereby maintaining a constant mass.
3. (C) It should absorb moisture from the air and react immediately and stoichiometrically with another chemical: This statement is false. A primary standard should not be hygroscopic (i.e., it should not absorb atmospheric moisture) as this would compromise its mass and, consequently, the titration's accuracy.
4. (D) It must be easily dissolvable in water: This statement is accurate. Dissolvability ensures complete dissolution of the compound, facilitating a consistent and precise reaction.
5. (E) KMnO₄ & NaOH are suitable as primary standards: This statement is false. KMnO₄ is not employed as a primary standard due to its tendency to degrade and its atmospheric instability. Likewise, NaOH is hygroscopic, absorbing atmospheric water and carbon dioxide, rendering it unsuitable for use as a primary standard.

Following this evaluation, statements (C) and (E) are deemed incorrect.