Brønsted–Lowry Acids and Bases
What Is the Brønsted–Lowry Theory?
Definition
Brønsted–Lowry theory
The Brønsted–Lowry theory, introduced in 1923, defines acids and bases based on their ability to transfer protons (H⁺ ions).
This framework expanded earlier definitions and applies to a wide variety of chemical reactions, even beyond water-based systems.
Definition
Brønsted–Lowry acid
A Brønsted–Lowry acid is a proton (H⁺) donor, which gives up a hydrogen ion in a reaction.
Definition
Brønsted–Lowry base
A Brønsted–Lowry base is a proton (H⁺) acceptor, which gains a hydrogen ion in a reaction.
Consider the reaction between hydrogen chloride (HCl) and ammonia (NH₃):
$$
\text{HCl} + \text{NH}_3 \rightarrow \text{NH}_4^+ + \text{Cl}^-
$$
Here:
- HCl acts as a Brønsted–Lowry acid because it donates an H⁺ ion.
- NH₃ acts as a Brønsted–Lowry base because it accepts the H⁺ ion.
- Unlike earlier theories, the Brønsted–Lowry theory is not restricted to aqueous solutions.
- It applies to reactions in gases, liquids, and even non-aqueous solvents, making it a more flexible model.
Representing Acids and Bases in Aqueous Solutions
- In aqueous (water-based) systems, acids and bases interact with water.
- A key concept here is the hydronium ion:
- A free proton (H⁺) does not exist independently in water.
