How is a base defined?

A base is defined as a substance that accepts protons (H⁺ ions) or donates hydroxide ions (OH⁻) in a chemical reaction. This definition stems from the Brønsted-Lowry theory of acids and bases, which emphasizes the role of protons in determining whether a substance acts as an acid or a base. In aqueous solutions, bases can directly increase the concentration of hydroxide ions, which in turn will react with hydrogen ions. The ability to accept protons or provide hydroxide ions is fundamental to the characteristic behavior of bases in chemical reactions.

Understanding this definition helps differentiate bases from acids and other types of substances based on their reactions in solution. For instance, while an acid donates protons (and increases H⁺ concentration), a base can do the opposite by either accepting protons or providing hydroxide ions.