Acids and bases are two classes of chemical substances that differ in their properties and behavior. An acid is a compound that releases hydrogen ions (H+) when dissolved in water, resulting in a decrease in pH. A base, on the other hand, is a compound that can accept a hydrogen ion, thereby increasing the pH. This is commonly known as the Arrhenius theory of acids and bases.

The Brønsted–Lowry theory expands upon the Arrhenius model by defining an acid as a proton (H+) donor and a base as a proton acceptor. This is important because it allows for more flexibility in identifying acidic and basic species. For example, ammonia (NH3) is considered a base because it can accept a proton, even though it does not produce hydroxide ions (OH-) like traditional bases.

Buffers are chemical substances that help maintain a stable pH in a solution. They are composed of a weak acid and its corresponding conjugate base. When an acid or base is added to a buffered solution, the buffer reacts to limit the change in pH by either accepting or donating protons. In other words, buffers help resist changes in pH by neutralizing added acids or bases.

Buffer systems play an important role in many biological processes, as they help regulate the pH of bodily fluids such as blood and prevent large changes in pH that could be harmful to cells. Common examples of buffer systems include the bicarbonate buffer system in the blood and the phosphate buffer system in cells.

Overall, acids, bases, and buffers are important concepts in chemistry and have numerous applications in science and everyday life. Understanding these topics can help explain many chemical reactions and phenomena, from the sourness of citrus fruits to the acidity of stomach acid.