What is defined as a substance that yields a hydrogen ion when ionized?

The term that describes a substance which yields a hydrogen ion (H+) when ionized is indeed an acid. Acids are characterized by their ability to donate protons (hydrogen ions) into a solution. This property is fundamental to understanding acid-base chemistry.

When an acid dissolves in water, it dissociates to release hydrogen ions. This increase in hydrogen ion concentration causes the pH of the solution to decrease, making it more acidic. This behavior is not shared by bases, salts, or buffers, which either do not release hydrogen ions or have different functions in solution.

A base typically accepts hydrogen ions and can sometimes produce hydroxide ions instead. Salts are products of the neutralization reaction between an acid and a base, consisting of ions that do not release hydrogen ions directly. Buffers, on the other hand, resist changes in pH when acids or bases are added, generally involving a weak acid and its conjugate base, but they do not fit the definition of a substance that yields hydrogen ions upon ionization. Understanding these distinctions is key to grasping concepts in biochemistry and its applications in biotechnology.