What are diprotic and triprotic acids? List an example of each.
The correct answer and explanation is:
Diprotic Acids:
A diprotic acid is an acid that can donate two protons or hydrogen ions (H⁺) per molecule during the dissociation process. The two hydrogen ions are released in two stages, with the acid typically undergoing two dissociation steps. This ability is due to the presence of two acidic hydrogen atoms in the molecule, which can dissociate when the acid dissolves in water.
Example of Diprotic Acid:
An example of a diprotic acid is sulfuric acid (H₂SO₄). When sulfuric acid is dissolved in water, it dissociates in two steps. In the first step, it dissociates to form hydrogen ions (H⁺) and hydrogen sulfate ions (HSO₄⁻). In the second step, the hydrogen sulfate ion can further dissociate to release another hydrogen ion (H⁺), forming sulfate ions (SO₄²⁻).
- H₂SO₄ → H⁺ + HSO₄⁻
- HSO₄⁻ → H⁺ + SO₄²⁻
Triprotic Acids:
A triprotic acid, on the other hand, is an acid that can donate three protons (H⁺) per molecule in three stages of dissociation. Each hydrogen ion is released sequentially, with each stage requiring energy for dissociation. Triprotic acids have three acidic hydrogen atoms, and they undergo three dissociation steps. These types of acids are less common than diprotic acids because of the additional energy required to remove all three protons.
Example of Triprotic Acid:
An example of a triprotic acid is phosphoric acid (H₃PO₄). When phosphoric acid is dissolved in water, it dissociates in three steps.
- H₃PO₄ → H⁺ + H₂PO₄⁻
- H₂PO₄⁻ → H⁺ + HPO₄²⁻
- HPO₄²⁻ → H⁺ + PO₄³⁻
Explanation:
The key difference between diprotic and triprotic acids lies in the number of hydrogen ions they can release. Both types of acids exhibit successive dissociation, but the triprotic acid releases three hydrogen ions, while the diprotic acid only releases two. The first dissociation step in both cases is typically the strongest (most exothermic), and as more protons are released, the dissociation becomes progressively weaker. This distinction is essential in understanding the acid strength and how these acids behave in aqueous solutions.