Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R:…

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R:

Assertion A: pKa 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:

  1. A is true but R is false
  2. A is false but R is true
  3. Both A and R are true and R is the correct explanation of A
  4. Both A and R are true but R is NOT the correct explanation of A.

Solution

pKa is a measure of  the acidity of a particular molecule. It measures the strength of an acid by how tightly a proton is held by a Bronsted acid. The lower the value of pKa, the stronger the acid and the greater its ability to donate its protons. describe the acidity of a particular molecule.

pKa=-logKa

Hence, Assertion is true,

Phenol is more acidic than ethanol because after losing a proton H+, phenol forms phenoxide ion which is stabilised by resonance whereas ethoxide ion is not.

Asked in: JEE Main 2024 (31 Jan Shift 1)

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