Hydrogen ion concentration in aqueous solution ([H⁺] (also represented as [H₃O⁺]))

The hydrogen ion concentration in aqueous solution quantifies the amount of free hydrogen ions (protons, H⁺) or hydronium ions (H₃O⁺) present in water-based solutions and is the fundamental chemical property underlying the pH scale. The pH is defined as the negative logarithm of the hydrogen ion (or hydronium ion) concentration: \( \text{pH} = -\log[H^+] \)[1][2][3][4][5]. In pure water at 25°C, [H⁺] = 1 × 10⁻⁷ mol/L and pH = 7. Changes in hydrogen ion concentration are central to acid-base chemistry and influence a wide range of biological and chemical processes. However, "hydrogen ion concentration" is not a molecular entity, receptor, enzyme, or drug target, but a measurable property of aqueous systems that reflects solution acidity or basicity[3][4][5][7]. Hydrogen ion concentration is directly linked to processes such as acid-base balance in physiology and environmental chemistry (e.g., ocean acidification), but is not itself a specific molecular target for drug action[7]. Key point: This entry refers to a fundamental chemical property rather than a definable drug target or molecular entity. Therefore, it is not appropriate as a canonical therapeutic target in drug discovery or molecular pharmacology contexts.

Other names

Hydrogen ion concentrationProton concentrationHydronium ion concentration[H⁺][H₃O⁺]pH (logarithmic expression)

Not applicable