Chemistry Carboxylic Acids SZABMU 2023
PMDC Verified Question 24 of 94
The relative acidic strength of phenol, water, alcohol & carboxylic acid is:
A
\( -\text{COOH} > \text{H}_2\text{O} > \text{C}_6\text{H}_5\text{OH} > -\text{OH} \)
B
\( -\text{COOH} > \text{C}_6\text{H}_5\text{OH} > \text{H}_2\text{O} > -\text{OH} \)
C
\( -\text{COOH} > -\text{OH} > \text{C}_6\text{H}_5\text{OH} > \text{H}_2\text{O} \)
D
\( -\text{COOH} > \text{H}_2\text{O} > -\text{OH} > \text{C}_6\text{H}_5\text{OH} \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: \( -\text{COOH} > \text{C}_6\text{H}_5\text{OH} > \text{H}_2\text{O} > -\text{OH} \)
Concept:

Acid strength correlates directly with the stability of the conjugate base. Resonance stabilization heavily favors stronger acidity.

Solution:

  • Carboxylic acid (\( -\text{COOH} \)): The carboxylate ion is immensely stabilized by equivalent resonance over two oxygen atoms. (Strongest)


  • Phenol (\( \text{C}_6\text{H}_5\text{OH} \)): The phenoxide ion is stabilized by resonance into the aromatic ring, making it fairly acidic.


  • Water (\( \text{H}_2\text{O} \)): The hydroxide ion lacks resonance but has no destabilizing alkyl groups.


  • Aliphatic Alcohol (\( -\text{OH} \)): The alkoxide ion is destabilized by the electron-donating inductive effect (\( +I \)) of the alkyl chain. (Weakest)


Why other options are incorrect:

Option B is the universally accepted chemical order of acidity for these standard functional classes.

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