Monoprotic Acid Definition

A monoprotic acid donates only one proton or hydrogen atom per molecule to an aqueous solution. This is in contrast to acids capable of donating more than one proton/hydrogen, which are called polyprotic acids. Polyprotic acids may be further categorized according to how many protons they can donate (diprotic = 2, triprotic = 3, etc.).

The electrical charge of a monoprotic acid jumps one level higher before it gives away its proton. Any acid that contains just one hydrogen atom in its formula is monoprotic, but some acids that contain more than one hydrogen atom are also monoprotic. In other words, all single-hydrogen acids are monoprotic but not all monoprotic acids contain only a single hydrogen.

Because only one hydrogen is released, the pH calculation for a monoprotic acid is fairly straightforward and predictable. A monoprotic base will only accept a single hydrogen atom. See below for examples of acids that donate only one proton or hydrogen in solution and their chemical formulas.

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Polyprotic Acid Definition in Chemistry

By Anne Marie Helmenstine, Ph.D.

Monoprotic Acid Examples

Hydrochloric acid (HCl) and nitric acid (HNO₃) are common monoprotic acids. Although it contains more than one hydrogen atom, acetic acid (CH₃COOH) is also a monoprotic acid as it dissociates to release only a single proton.

Polyprotic Acid Examples

The following examples are polyprotic acids that either fall under the category of diprotic or triprotic.

Diprotic acids

1. Sulfuric acid: H₂SO₄
2. Carbonic acid: H₂CO₃
3. Oxalic acid: C₂H₂O₄ 

Triprotic acids

1. Phosphoric acid: H₃PO₄
2. Arsenic acid: H₃AsO₄
3. Citric acid: C₆H₈O₇