
In chemistry, a monoprotic acid is an acid that donates one hydrogen ion (H+) or proton per molecule when it dissociates in water. Another name for a monoprotic acid is a monobasic acid. A monoprotic acid (HA) dissociates according to the following process:
HA (aq) + H2O (l) ⇌ H3O+ (aq) + A− (aq)
Examples of Monoprotic Acids
Monoprotic acids include both strong acids and weak acids. Acids that contain a single hydrogen (H) atom are obvious example, but some acids with multiple hydrogen atoms also qualify. For example, organic acids that contain one carboxylic acid group (R−COOH or R−CO2H) are monoprotic.
Here are examples of monoprotic acids:
- Acetic acid (CH3COOH)
- Benzoic acid (C6H5COOH)
- Formic acid (HCOOH)
- Hydrobromic acid (HBr)
- Hydrochloric acid (HCl)
- Hydrofluoric acid (HF)
- Hydroiodic acid (HI)
- Nitric acid (HNO3)
Examples of Polyprotic Acids
Polyprotic acids donate more than one hydrogen or proton when they dissociate. A diprotic acid donates two protons, while a triprotic acid donates three protons. The subsequent loss of each proton becomes more unfavorable, but all of a polyprotic acid’s conjugate bases exist in aqueous solution.
Diprotic Acids
Look for H2 within the formula of a diprotic acid:
- Sulfuric acid: H2SO4
- Carbonic acid: H2CO3
- Oxalic acid: C2H2O4
Triprotic Acids
- Phosphoric acid: H3PO4
- Arsenic acid: H3AsO4
- Citric acid: C6H8O7
How to Identify Monoprotic Acids
Two ways of identifying monoprotic acids are by their chemical formulas and by their titration curves.
A monoprotic acid either contains a single hydrogen atom (e.g., HCl) or else a single carboxylic acid group (e.g;, CH3COOH).
The graph of a monoprotic acid titration shows a single equivalence point. In contrast, a diprotic acid has two equivalence points and a triprotic acid has three equivalence points.
References
- Ebbing, Darrell; Gammon, Steven D. (January 1, 2016). General Chemistry. Cengage Learning. ISBN 9781305887299.
- Petrucci R.H., Harwood, R.S.; Herring, F.G. (2002). General Chemistry (8th ed.). Prentice-Hall. ISBN 0-13-014329-4.
- Skoog, D.A; West, D.M.; Holler, J.F.; Crouch, S.R. (2004). Fundamentals of Analytical Chemistry (8th ed.). Thomson Brooks/Cole. ISBN 0-03-035523-0.
- Zumdahl, Steven S. (1997). Chemistry (4th ed.). Boston: Houghton Mifflin. ISBN 9780669417944.