Chemistry Alcohols & Phenols ETEA 2022
PMDC Verified Question 43 of 95
Which of the following compounds is most acidic?
A
Water
B
Ethanol
C
Phenol
D
Cyclohexanol
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Phenol
Concept:

Acidic strength corresponds to the stability of the anion formed after proton loss.

Formula:

Not applicable to this conceptual question.

Solution:

  • When phenol loses a proton, it forms the phenoxide ion, which is stabilized by resonance across the benzene ring.


  • Water, ethanol, and cyclohexanol lack any \(\pi\)-system to delocalize the negative charge on their resulting hydroxide or alkoxide ions.


  • Consequently, phenol is significantly more acidic than the aliphatic and inorganic alternatives provided.


Why other options are incorrect:

The \(K_a\) of phenol (\(\approx 10^{-10}\)) is much higher than water (\(\approx 10^{-14}\)) and ethanol/cyclohexanol (\(\approx 10^{-16}\)).

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