In the study of chemistry, bases are defined as substances that decrease the concentration of hydrogen ions (H⁺) in a solution, making them the counterpart to acids, which increase hydrogen ion concentration. A common example of a base is sodium hydroxide, represented by the chemical formula NaOH.

When sodium hydroxide is added to water, it undergoes a process called dissociation, where it breaks apart into sodium ions (Na⁺) and hydroxide ions (OH^-). For instance, if three molecules of sodium hydroxide are introduced to water, they will dissociate into three sodium ions and three hydroxide ions. This dissociation is crucial as it illustrates how bases interact with water.

Even in pure water, there exists a small concentration of hydrogen ions due to the autoionization of water, which is a process where water molecules spontaneously form hydrogen ions and hydroxide ions. When hydroxide ions from sodium hydroxide encounter hydrogen ions in the solution, they react to form water molecules (H₂O). This reaction effectively reduces the concentration of hydrogen ions in the solution.

For example, if there were initially three hydrogen ions present in the water, after the addition of sodium hydroxide, these hydrogen ions would react with the hydroxide ions, resulting in a decrease in the overall hydrogen ion concentration. This is a key characteristic of bases: they lower the concentration of hydrogen ions in a solution, which is vital for various biological and chemical processes.

Understanding the role of bases and their ability to alter hydrogen ion concentrations is essential, as these changes can significantly impact living systems and chemical reactions. As we continue our exploration of acids and bases, we will delve deeper into their properties and applications.