# What is the difference between carboxylate ions and groups?

I would like to know the difference between carboxylate ions carboxyl groups? An example is is $\ce{COOH}$ and $\ce{COO}$.

### Carboxyl

The carboxyl group $$\ce{-COOH}$$ is an organic functional group consisting of a carbon atom double bonded to an oxygen atom and single bonded to a hydroxyl group.

Compounds with a carboxyl group are called carboxylic acids (e.g. acetic acid, $$\ce{CH2COOH}$$).

### Carboxylate

A carboxylate $$\ce{-COO^-}$$ is a salt or ester of a carboxylic acid. For example, acetic acid reacts with sodium bicarbonate to form sodium acetate.

Compounds with this group have the carboxy- prefix or -ate suffix (e.g. sodium acetate $$\ce{CH3COONa}$$). When these salts are ionised (e.g. dissolved in water), the anion with the carboxylate group is called a carboxylate ion.

The carboxylate ion is the negative ion (anion) formed as the conjugate base when a carboxylic acid loses a proton.

$$\ce{R-COOH -> R-COO^- + H+}$$

Being its conjugate base, sodium acetate mixed with acetic acid makes a useful buffer solution for many biochemical reactions where a 'mildly acidic' pH of 4-6 is desired.

• I suppose it must be hard not to see the big $\ce{H}$ difference. – Poutnik Mar 29 at 12:49
• You mean answer: a proton – theo Apr 24 at 0:16