alcohol acidity

Alcohols are weak acids — much weaker than vinegar, but real acids all the same. The acidic proton is the one on the -OH group, and an alcohol can hand it off to a strong enough base, becoming an alkoxide ion. With a pKa around 16 to 18 (ethanol is about 16), an alcohol is roughly as acidic as water (pKa 15.7) and a hundred-trillion times weaker than a carboxylic acid (pKa around 4 to 5).

How acidic a particular alcohol is depends on how stable its alkoxide is — the more comfortable the molecule is with the negative charge after losing the proton, the more readily it lets the proton go. Electron-withdrawing groups nearby pull negative charge away and stabilise the alkoxide, raising acidity: 2,2,2-trifluoroethanol (CF3-CH2-OH) is far more acidic than ethanol because three fluorines tug the charge away by the inductive effect. Bulkier alkyl groups, which are weakly electron-donating and also crowd the solvent out, push the other way, so tert-butanol is slightly less acidic than methanol.

This modest acidity is enough to matter in the lab. It means alcohols react with reactive metals to give alkoxides, and it explains why you need a base stronger than hydroxide to deprotonate an alcohol fully. The far greater acidity of phenols (pKa around 10), where the negative charge is spread into an aromatic ring by resonance, is best appreciated against this baseline of ordinary, weakly acidic alcohols.