Acid–base reactions:
The phenoxide ion is stabilized via the resonance and delocalization of the negative charge into the ring that means that phenoxide ions are weaker bases as compared to the alkoxide ions. In turn this means that phenols are more acidic than alcohols, but less acidic than carboxylic acids. The pKa values of several phenols are in the order of 11, as compared to 18 for alcohols and 4.74 for acetic acid.
The meaning of this is that the phenols can be ionized with weaker bases than those needed to ionize alcohols, but need stronger bases than those required to ionize carboxylic acids. For instance, phenols are ionized through sodium hydroxide but not by the weaker base sodium hydrogen carbonate. Alcohols being much less acidic are not ionized by either base while carboxylic acids are ionized via both sodium hydroxide and sodium hydrogen carbonate solutions.
These acid-base reactions allow a simple way of distinguishing among most carboxylic acids, phenols, and alcohols. Because the salts made from the acid-base reaction are water soluble, compounds consisting of these functional groups can be distinguished through testing their solubilities in sodium hydrogen carbonate and sodium hydroxide solutions. This solubility test is not suitable for low molecular weight structures like methanol or ethanol because these are water soluble and dissolve in basic solution due to their water solubility rather than their ability to form salts.