Carboxylic acids are weak acids that can release a hydrogen ion (H⁺) from their –COOH group. They are stronger acids than alcohols and phenols, mainly because the ion left behind after losing hydrogen (called the carboxylate ion) is stable. This stability comes from resonance, where the negative charge is spread evenly over both oxygen atoms.
Their acidity depends on several factors:
- Resonance makes the acid stronger by stabilizing the negative ion.
- Inductive effect of electronegative groups like chlorine or nitro near the –COOH group increases acidity, while alkyl groups reduce it.
- Hydrogen bonding in water helps them ionize more easily.
- Chain length of the hydrocarbon part slightly affects acidity: longer chains make them weaker.
In general, simple carboxylic acids have a strength similar to weak acids, but they are definitely stronger than alcohols and phenols.
In short, carboxylic acids are weak but important acids, and their acidity comes from the stability of the ion formed after losing hydrogen.