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

Step 1: Analyze Assertion (A)
In volumetric analysis, the concentration of the solutions used must be known accurately. KOH solutions are commonly used as titrants in acid-base titrations. The concentration of a KOH solution can change over time due to various factors. Therefore, it’s crucial to check and standardize its concentration before use. Assertion (A) is correct.
Step 2: Analyze Reason (R)
KOH solutions absorb atmospheric carbon dioxide (\(\text{CO}_2\)). The reaction between KOH and \(\text{CO}_2\) forms potassium carbonate (\(\text{K}_2\text{CO}_3\)) and water:
\[2\text{KOH} + \text{CO}_2 \rightarrow \text{K}_2\text{CO}_3 + \text{H}_2\text{O}.\]
This reaction consumes KOH, reducing its concentration in the solution. Hence, Reason (R) is correct.
Step 3: Analyze the Relationship between (A) and (R)
The absorption of atmospheric \(\text{CO}_2\) by KOH solution directly affects its concentration. This is the primary reason why the concentration of a KOH solution needs to be checked before use, especially if it’s an older solution. Thus, Reason (R) is the correct explanation for Assertion (A).