What is the term used to describe when water acts as an acid/base with itself?

The term that describes when water acts as an acid or base with itself is autoionization. This process occurs when two water molecules interact to form hydronium (H₃O⁺) and hydroxide (OH⁻) ions. Essentially, one water molecule donates a proton (H⁺) to another water molecule, which functions as a base. This equilibrium between water molecules is a fundamental concept in understanding acid-base chemistry and the self-ionization of water, which is crucial in defining the pH scale and the properties of aqueous solutions.

In contrast, ionization generally refers to the process where a neutral atom or molecule gains or loses electrons to form ions, often involving solutes in a solvent rather than water with itself. Hydrolysis typically involves the reaction of a compound with water, often in a chemical reaction where ions are formed from the compound instead of simply from the water's self-reaction. Dissociation is the process by which a compound separates into its constituent ions, which does not specifically involve water acting upon itself. Thus, autoionization effectively captures the unique interaction of water molecules with each other in the context of acid-base chemistry.