Question

Arrange the following in increasing order of acid strength: phenol, ethanol, water.

Hint:

The acidity of alcohols and phenols increases with the ability to stabilize the conjugate base. Phenols are more acidic due to the resonance stabilization of the phenoxide ion.

Answer 1

To order these compounds by increasing acid strength, we evaluate their proton-donating capabilities. Enhanced proton (H\(^+\)) donation correlates with greater acid strength.
1. Ethanol (CH\(_3\)CH\(_2\)OH): Ethanol's hydroxyl group (-OH) makes it a considerably weaker acid than water or phenol.
2. Water (H\(_2\)O): Water is neutral but exhibits weak acidic properties, capable of donating a proton to yield \( OH^- \).
3. Phenol (C\(_6\)H\(_5\)OH): Phenol surpasses both ethanol and water in acidity due to the resonance stabilization of the phenoxide ion (C\(_6\)H\(_5\)O\(^-\)) post-proton donation.
The sequence of increasing acid strength is: \[\text{Ethanol} < \text{Water} < \text{Phenol}\]