Given below are two statements:
One is labelled as Assertion A and the other is labelled as Reason R:
Assertion A: \(pK_a\) value of phenol is 10.0 while that of ethanol is 15.9.
Reason R: Ethanol is stronger acid than phenol.
In the light of the above statements, choose the correct answer from the options given below:
One is labelled as Assertion A and the other is labelled as Reason R:
Assertion A: \(pK_a\) value of phenol is 10.0 while that of ethanol is 15.9.
Reason R: Ethanol is stronger acid than phenol.
In the light of the above statements, choose the correct answer from the options given below:
- A is true but R is false.
- A is false but R is true.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is NOT the correct explanation of A.
The Correct Option is A
Approach Solution - 1
The problem involves understanding the acidity of phenol and ethanol, characterized by their \( pK_a \) values.
- Understanding \( pK_a \) Value:
- \( pK_a \) is the negative logarithm of the acid dissociation constant (\( K_a \)), an indicator of the strength of an acid.
- The lower the \( pK_a \) value, the stronger the acid, as it indicates a greater tendency to lose a proton (H+).
- Given Data:
- \( pK_a \) of phenol = 10.0
- \( pK_a \) of ethanol = 15.9
- Assertion (A):
- The assertion states that the \( pK_a \) value of phenol is 10.0, while that of ethanol is 15.9. This is true.
- Reason (R):
- The reason claims that ethanol is a stronger acid than phenol. This is false because, as explained, lower \( pK_a \) means a stronger acid, and phenol has a lower \( pK_a \) than ethanol.
- Conclusion:
- Considering the values and their implications, the correct option is: A is true but R is false.
Approach Solution -2
Phenol is more acidic than ethanol because the conjugate base of phenoxide is more stable than ethoxide due to resonance stabilization in phenoxide.
Thus, the correct answer is Option A.
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