The Acidic Environment > 3. Acids >
Define acids as proton donors and describe the ionisation of acids in water
- The Lowry-Bronsted theory defines an acid as a substance that acts as a proton donor.
- When an acid molecule is in water, it can ionise, releasing a proton, or hydrogen ion, and forming a negative ion.
- The proton, or hydrogen ion, is donated to a water molecule, forming a hydronium ion:
- For example, in the case of hydrochloric acid:
- Acids can be classified according to their potential for proton donation per molecule:
- Monoprotic acids: Acids that can release only one proton, or hydrogen ion, per molecule.
- Diprotic acids: Acids that can release up to two protons, or hydrogen ions, per molecule.
- Triprotic acids: Acids that can release up to three protons, or hydrogen ions, per molecule.
Ionisation/Dissociation of acetic acid in water (click to enlarge)