Monoprotic Acid Definition and Examples

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Monoprotic Acid Definition and Example
A monoprotic acid donates one proton or hydrogen when it dissociates.

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:

  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

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.