In chemistry, hydronium is the common name for the cation H₃O⁺. Chemistry (in Greek: χημεία) is the science of matter and its interactions with energy and itself (see physics, biology). ... A cation is an ion with positive charge. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... This article is about the chemical element oxygen. ...

Nomenclature

According to IUPAC ion nomenclature, it should be referred to as "oxonium." Hydroxonium may also be used unambiguously to identify this ion. A draft IUPAC proposal recommends the use of oxonium and oxidanium in organic and inorganic chemistry contexts, respectively. IUPAC nomenclature is a systematic way of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). ... The International Union of Pure and Applied Chemistry (IUPAC) is an international non-governmental organization devoted to the advancement of chemistry. ...

Acids and Acidity

Hydronium is the cation that forms from water in the presence of hydrogen ions. These hydrons do not exist in a free state: they are extremely reactive and are solvated by water. An acid is generally the source of these hydrons; however, since water can behave as an acid, hydronium exists even in pure water. This special case of water reacting with water to produce hydronium (and hydroxide) ions is commonly known as the self-ionization of water. The resulting hydronium ions are few and short-lived. Water is in dynamic equilibrium between the liquid and solid states at standard temperature and pressure. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... IUPAC nomenclature is a systematic way of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). ... Solvation is the attraction and association of molecules of a solvent with molecules or ions of a solute. ... An acid (often represented by the generic formula AH) is typically a water-soluble, sour-tasting chemical compound. ... Hydroxide is a polyatomic ion consisting of oxygen and hydrogen: −O−H It has a charge of −1. ... The self-ionization of water is the chemical reaction in which two water molecules react to produce a hydronium (H3O+) and a hydroxide ion (OH-): The reaction is also known as the autoionization or autodissociation of water. ...

Hydronium is very acidic: at 25°C, its pKa=-1.7. It is also the most acidic species that can exist in water (assuming sufficient water for dissolution): any stronger acid will ionize and protonate a water molecule to form hydronium. The acidity of hydronium is the implicit standard used to judge the strength of an acid in water: strong acids must be better proton donors than hydronium, otherwise a significant portion of acid will exist in an non-ionized state. Unlike the hydronium that results from water's autodissociation, these hydronium ions are long-lasting and concentrated, in proportion to the strength of the dissolved acid. In chemistry and biochemistry, acid dissociation constant, the acidity constant, or the acid-ionization constant () is a specific type of equilibrium constant that indicates the extent of dissociation of hydrogen ions from an acid. ... A strong acid is an acidic compound which ionizes completely in an aqueous solution. ...

The pH of a solution is a measure of its proton concentration. Since these protons react with water to form hydronium, the acidity of an aqueous solution is determined by its hydronium concentration. click here for more info The title of this article is incorrect because of technical limitations. ...

Solvation

Researchers have yet to fully characterize the solvation of hydronium ion in water, in part because many different meanings of solvation exist. A freezing point depression study determined that the mean hydration ion in cold water is approximately H₃O⁺(H₂O)₆ (1): on average, each hydronium ion is solvated by 6 water molecules which are unable to solvate other solute molecules.

Some hydration structures are quite large: the H₃O⁺(H₂O)₂₀ magic ion number structure (called magic because of its increased stability with respect to hydration structures involving a comparable number of water molecules) might place the hydronium inside a dodecahedral cage (2). Because of the reactivity of the proton, it does not necessarily need to be associated with the water molecule in the centre of the cage. It could easily move around and be associated with any of the enclosing molecules. A dodecahedron is a Platonic solid composed of twelve pentagonal faces, with three meeting at each vertex. ...

Two other well-known structures are the Zundel and Eigen cations. Eigen placed the hydronium ion at the centre of an H₉O₄⁺ complex in which the hydronium is strongly hydrogen-bonded to 3 neighbouring water molecules (3). Eigen proposed an H₅O₂⁺ complex, in which the proton is shared equally by two water molecules (4). Recent work indicates that both of these complexes represent ideal structures in a more general hydrogen bond network defect (5). http://www. ...

Solid hydronium salts

For many strong acids, it is possible to form crystals of their hydronium salt that are relatively stable. Sometimes these salts are called acid monohydrates. As a rule, any acid with an ionization constant of 10⁹ or higher may do this. Acids whose ionization constant is below 10⁹ generally cannot form stable H₃O⁺ salts. For example, hydrochloric acid has an ionization constant of 10⁷, and mixtures with water at all proportions are liquid at room temperature. However, perchloric acid has an ionization constant of 10¹⁰, and if liquid anhydrous perchloric acid and water are combined in a 1:1 molar ratio, solid hydronium perchlorate forms. A strong acid is an acidic compound which ionizes completely in an aqueous solution. ... In chemistry and biochemistry, acid dissociation constant, the acidity constant, or the acid-ionization constant (Ka) is a specific type of equilibrium constant that indicates the extent of dissociation of hydrogen ions from an acid. ... The chemical substance hydrochloric acid is the aqueous (water-based) solution of hydrogen chloride (HCl) gas. ... Perchloric acid has the formula HClO4 and is a colorless liquid soluble in water. ...

References

1. Zavitsas, A. A. (2001) Properties of water solutions of electrolytes and nonelectrolytes. J. Phys. Chem. B 105 7805-7815.
2. Hulthe, G.; Stenhagen, G.; Wennerström, O. & C-H. Ottosson, C-H. (1997) Water cluster studied by electrospray mass spectrometry. J. Chromatogr. A 512 155-165.
3. Zundel, G. & Metzger, H. (1968) Energiebänder der tunnelnden Übershuß-Protenon in flüssigen Säuren. Eine IR-spektroskopische Untersuchung der Natur der Gruppierungen H₅O₂⁺ Z. Phys. Chem. 58 225-245.
4. Wicke, E.; Eigen, M. & Ackermann, Th. (1954) Über den Zustand des Protons (Hydroniumions) in wäßriger Lösung. Z. Phys. Chem. 1 340-364.
5. Marx, D.; Tuckerman, M. E.; Hutter, J. & Parrinello, M. (1999) The nature of the hydrated excess proton in water. Nature 397 601-604.