Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R) Assertion (A) : An aqueous solution of KOH when used for volumetric analysis, its concentration should be checked before the use. Reason (R) : On aging, KOH solution absorbs atmospheric CO_2 . In the light of the above statements, choose the correct answer from the options given below :

Both (A) and (R) are correct and (R) is the correct explanation of (A)

(A) is correct but (R) is not correct

(A) is not correct but (R) is correct

Both (A) and (R) are correct but (R) is not the correct explanation of (A)

Electrochemistry PYQ — JEE Main 2023 · 1 Feb · Shift 2 · Q12 with Solution

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Correct answer: D

Understand the assertion
Assertion (A): An aqueous solution of $\mathrm{KOH}$ when used for volumetric analysis, its concentration should be checked before use.

This is correct. In volumetric analysis, $\mathrm{KOH}$ solution is not a primary standard solution because its concentration may change on standing.
Understand the reason
Reason (R): On aging, $\mathrm{KOH}$ solution absorbs atmospheric $\mathrm{CO_2}$ .

This is also correct. Potassium hydroxide is hygroscopic and also reacts with carbon dioxide from air: $2\mathrm{KOH} + \mathrm{CO_2} \rightarrow \mathrm{K_2CO_3} + \mathrm{H_2O}$
Link between Assertion and Reason
Because $\mathrm{KOH}$ absorbs $\mathrm{CO_2}$ from the atmosphere, part of the hydroxide is converted into potassium carbonate. Hence, the actual concentration of $\mathrm{KOH}$ changes with time.

Therefore, before using it in volumetric analysis, its concentration must be checked/standardized.
Evaluate the options
- A: $(A)$ is correct but $(R)$ is not correct $\rightarrow$ False
- B: $(A)$ is not correct but $(R)$ is correct $\rightarrow$ False
- C: Both are correct but $(R)$ is not the correct explanation $\rightarrow$ False
- D: Both are correct and $(R)$ is the correct explanation $\rightarrow$ True
Final conclusion
The correct option is D.

View written solutionFree

Correct answer: D

Understand the assertion
Assertion (A): An aqueous solution of $\mathrm{KOH}$ when used for volumetric analysis, its concentration should be checked before use.

This is correct. In volumetric analysis, $\mathrm{KOH}$ solution is not a primary standard solution because its concentration may change on standing.
Understand the reason
Reason (R): On aging, $\mathrm{KOH}$ solution absorbs atmospheric $\mathrm{CO_2}$ .

This is also correct. Potassium hydroxide is hygroscopic and also reacts with carbon dioxide from air: $2\mathrm{KOH} + \mathrm{CO_2} \rightarrow \mathrm{K_2CO_3} + \mathrm{H_2O}$
Link between Assertion and Reason
Because $\mathrm{KOH}$ absorbs $\mathrm{CO_2}$ from the atmosphere, part of the hydroxide is converted into potassium carbonate. Hence, the actual concentration of $\mathrm{KOH}$ changes with time.

Therefore, before using it in volumetric analysis, its concentration must be checked/standardized.
Evaluate the options
- A: $(A)$ is correct but $(R)$ is not correct $\rightarrow$ False
- B: $(A)$ is not correct but $(R)$ is correct $\rightarrow$ False
- C: Both are correct but $(R)$ is not the correct explanation $\rightarrow$ False
- D: Both are correct and $(R)$ is the correct explanation $\rightarrow$ True
Final conclusion
The correct option is D.