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 :

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

Answer 1

Answer: (D)

(C) and (E) only

Answer 2

A primary standard substance used in titrimetric analysis must satisfy the following criteria:

1. It should be available in pure and dry form.
2. It must not be hygroscopic (i.e., it should not absorb moisture) or undergo any chemical change in air.
3. It should be readily soluble in water.
4. KMnO 4 and NaOH are not suitable as primary standards due to their hygroscopic nature and tendency to absorb CO 2 from air, making them impure.

Incorrect Statements:

• (C): The substance should not be hygroscopic. Hence, this statement is incorrect.
• (E): Both KMnO 4 and NaOH are unsuitable as primary standards. This statement is also incorrect.

Final Answer is option (4).