Give an example of a monoprotic acid, a diprotic acid, and a triprotic acid.

When studying acids, understanding their capacity to donate protons is crucial. A monoprotic acid is the simplest type where the molecule can donate only one proton (or hydrogen ion, H⁺). This single proton release occurs when the acid dissolves in water. Hydrochloric acid (HCl) is a classic example of a monoprotic acid used frequently both in educational settings and industrial applications. Monoprotic acids are a fundamental concept in chemistry because they illustrate the most straightforward acid-base reaction.

Students often visualize this through the equation:
HCl → H⁺ + Cl^-.
This equation shows that in aqueous solution, hydrochloric acid disassociates to release one hydrogen ion and one chloride ion. Gaining familiarity with monoprotic acids sets a solid foundation for progressing to more complex acid types.

Scaling up the complexity, the next category is known as diprotic acids, which have the ability to donate two protons or hydrogen ions. Sulfuric acid (H₂SO₄) epitomizes this group with its two-stage disassociation in water. The recognition of two distinct stages is essential for understanding the unique properties of diprotic acids:

1. The first disassociation releases one hydrogen ion:
   H₂SO₄ → H⁺ + HSO₄^-.
2. The second disassociation releases another hydrogen ion:
   HSO₄^- → H⁺ + SO₄^2-.

The ability of diprotic acids to go through two disassociation steps influences their reactivity and the pH level of their solutions. This has implications in buffer solutions and titration experiments where understanding the sequential release of protons is important.

The most complex in our series is the triprotic acid, exemplified by phosphoric acid (H₃PO₄). These acids have the capacity to donate three protons, usually one at a time in a stepwise fashion. The multi-stage release of hydrogen ions makes them particularly interesting. For phosphoric acid, the disassociation happens as follows:

1. The first hydrogen ion is released:
   H₃PO₄ → H⁺ + H₂PO₄^-.
2. The second hydrogen ion is released:
   H₂PO₄^- → H⁺ + HPO₄^2-.
3. The final hydrogen ion is released:
   HPO₄^2- → H⁺ + PO₄^3-.

Because triprotic acids can release three distinct hydrogen ions, they can significantly affect a solution's pH and act as biological buffers. For instance, phosphoric acid plays a critical role in energy storage and transfer within the body. Understanding triprotic acids also allows students to explore more complex chemical and biochemical systems.