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.
Look for H2 within the formula of a diprotic acid:
- Sulfuric acid: H2SO4
- Carbonic acid: H2CO3
- Oxalic acid: C2H2O4
- 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.
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