Question

Which is the correct order of acid strength from the following?

• A. C$_6$H$_5$OH > H$_2$O > ROH
• B. C$_6$H$_5$OH > ROH > H$_2$O
• C. ROH > C$_6$H$_5$OH > H$_2$O
• D. H$_2$O > C$_6$H$_5$OH > ROH

Hint:

The acidity of alcohols, phenols, and water is governed by their ability to stabilize the negative charge after deprotonation.

Answer 1

The Correct Option is D

To solve this problem, we need to compare the acidity of phenol (C₆H₅OH), alcohol (ROH), and water (H₂O).

1. Understanding Acid Strength:
Acid strength depends on the ability of the molecule to donate a proton (H⁺). This is determined by the stability of the conjugate base formed after proton loss.

2. Phenol (C₆H₅OH) vs Alcohol (ROH):
Phenol is more acidic than alcohol because the negative charge on the oxygen in the phenoxide ion (C₆H₅O^-) is stabilized by resonance with the aromatic ring. In contrast, the negative charge on the oxygen in the alkoxide ion (RO^-) is not stabilized, making alcohol less acidic than phenol.

3. Phenol (C₆H₅OH) vs Water (H₂O):
Water (H₂O) is a weaker acid than phenol. Although water can donate a proton to form the hydroxide ion (OH^-), the conjugate base of phenol is more stable due to resonance stabilization.

4. Conclusion:
The correct order of acid strength is: Water > Phenol > Alcohol.

Final Answer:
The correct option is (D) H₂O > C₆H₅OH > ROH.