What is the Brønsted-Lowry definition of acids and bases?

The Brønsted-Lowry definition identifies acids as proton donors and bases as proton acceptors.

In more detail, the Brønsted-Lowry theory is a more comprehensive definition of acids and bases than the traditional Arrhenius definition. It was proposed independently by Johannes Nicolaus Brønsted and Thomas Martin Lowry in 1923. According to this theory, an acid is a substance that can donate a proton (H+) to another substance, while a base is a substance that can accept a proton from another substance. This definition expands the range of substances that can be classified as acids or bases, and it allows for the explanation of reactions in which no hydrogen ions are involved.

For example, in the reaction between ammonia (NH3) and water (H2O), ammonia accepts a proton from water, making it a Brønsted-Lowry base, while water donates a proton, making it a Brønsted-Lowry acid. The reaction can be represented as follows: NH3 + H2O ⇌ NH4+ + OH-. Here, water (H2O) donates a proton to ammonia (NH3), forming a hydroxide ion (OH-) and an ammonium ion (NH4+).

It's also important to note that the Brønsted-Lowry theory introduces the concept of conjugate acid-base pairs. In the above example, NH4+ is the conjugate acid of the base NH3, and OH- is the conjugate base of the acid H2O. A conjugate acid is the particle formed when a base accepts a proton, and a conjugate base is the particle formed when an acid donates a proton.

This theory is particularly useful in explaining acid-base reactions in solutions and helps to understand the behaviour of acids and bases in various chemical reactions. It's a fundamental concept in the study of chemistry, particularly in the field of acid-base chemistry.