Question

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 :

• A. (A) is correct but (R) is not correct
• B. (A) is not correct but (R) is correct
• C. Both $( A )$ and $( R )$ are correct but $(R)$ is not the correct explanation of $( A )$
• D. Both $( A )$ and $( R )$ are correct and $( R )$ is the correct explanation of $( A )$

Answer 1

The Correct Option is D

To analyze and determine the correctness of the statements given, let's delve into the chemistry involved with potassium hydroxide (\(KOH\)) in solution.

Assertion (A): An aqueous solution of \(KOH\) when used for volumetric analysis, its concentration should be checked before use.

Reason (R): On aging, \(KOH\) solution absorbs atmospheric \(CO_2\).

Let's examine each statement:

1. KOH and Volumetric Analysis: In volumetric analysis, the concentration of a solution must be precisely known. \(KOH\) solutions are used as titrants in analytical chemistry. Their accurate concentration is crucial for achieving precise and reliable results in titrations.
2. Absorption of Atmospheric \(CO_2\): Potassium hydroxide (\(KOH\)) is a strong base and can react with carbon dioxide (\(CO_2\)) from the air to form potassium carbonate (\(K_2CO_3\)), as shown in the reaction below:

\(2 \, \text{KOH (aq)} + \text{CO}_2 \, \text{(g)} \rightarrow \text{K}_2\text{CO}_3 \, \text{(aq)} + \text{H}_2\text{O} \, \text{(l)}\)

This reaction leads to a change in the composition and concentration of the \(KOH\) solution over time due to the consumption of \(KOH\) and the formation of \(K_2CO_3\).

Conclusion:

• Assertion (A) is correct because the concentration of \(KOH\) solutions should indeed be verified before use in volumetric analysis due to potential concentration changes.
• Reason (R) is correct as it correctly identifies that \(KOH\) absorbs \(CO_2\) from the atmosphere, impacting its concentration.
• (R) is the correct explanation for (A) as the absorption of \(CO_2\) directly causes the need to recheck the concentration of \(KOH\) solutions for accurate analysis.

Hence, the correct answer is: Both (A) and (R) are correct and (R) is the correct explanation of (A).